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1
Mueller, Stephen F., Jonathan W. Mallard, Qi Mao, and Stephanie L. Shaw. "Variability of Natural Dust Erosion from a Coal Pile." Journal of Applied Meteorology and Climatology 54, no. 1 (January 2015): 3–14. http://dx.doi.org/10.1175/jamc-d-14-0126.1.
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AbstractA study of fugitive dust emissions from a pile of crushed coal revealed that, in addition to dust being emitted into the atmosphere during periods of pile-management (human) activity, it is also emitted during periods without human activity. This “natural” emission in itself is not surprising given past work on wind erosion of particulate matter from aggregate piles. However, hourly downwind measurements of fine particle (PM10) mass concentrations at two sites revealed that excessive dust was present in the air even when wind speeds were below the erosion threshold estimated from nearby wind speed measurements and regulatory guidance on coal pile aerodynamic characteristics. During periods of natural emissions with higher wind speeds, downwind concentrations were strongly associated with µ2—the squared excess of 1-min maximum wind speed above the erosion threshold—consistent with previous work on wind erosion potential. However, 88% of hourly concentrations coincided with lower winds for which wind speed was not a good predictor of airborne dust levels. Evidence was found that natural low-wind PM10 concentrations varied significantly with relative humidity, air temperature, and turbulence parameters (σu and σw). Smoke from coal combustion was ruled out as a significant factor in PM10 levels, but statistical evidence along with visual observation suggests that microscale turbulent airflows, including dust devils, were a significant source of PM10 during low wind speeds over the pile. The localized behavior of the turbulence makes it very difficult to develop a strong statistical model of natural downwind concentrations on the basis of off-pile meteorological measurements.
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Hernandez, C., P. Drobinski, S. Turquety, and J. L. Dupuy. "Size of wildfires in the Euro-Mediterranean region: observations and theoretical analysis." Natural Hazards and Earth System Sciences Discussions 3, no. 2 (February 9, 2015): 1203–30. http://dx.doi.org/10.5194/nhessd-3-1203-2015.
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Abstract. MODIS satellite observations of fire size and ERA-Interim meteorological reanalysis are used to derive a relationship between burnt area and wind speed over the Mediterranean region and Eastern Europe. As intuitively expected, the burnt area associated to the largest wildfires is an increasing function of wind speed in most situations. It is always the case in Eastern Europe. It is also the case in the Mediterranean for moderate temperature anomaly. In situations of severe heatwaves and droughts, the relationship between burnt area and wind speed displays bimodal shape. Burnt areas are large for low 10 m wind speed (lower than 2 m s−1), decrease for moderate wind speed values (lower than 5 m s−1 and larger than 2 m s−1) and increase again for large wind speed (larger than 5 m s−1). To explain such behavior fire propagation is investigated using a probabilistic cellular automaton model. The observed relationship between burnt area and wind speed can be interpreted in terms of percolation threshold which mainly depends on local terrain slope and vegetation state (type, density, fuel moisture). In eastern Europe, the percolation threshold is never exceeded for observed wind speeds. In the Mediterranean Basin we see two behaviors. During moderately hot weather, the percolation threshold is passed when the wind grows strong. On the other hand, in situations of severe Mediterranean heatwaves and droughts, moderate wind speed values impair the propagation of the wildfire against the wind and do not sufficiently accelerate the forward propagation to allow a growth of wildfire size.
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Scott, Nicholas, Tetsu Hara, Edward J. Walsh, and Paul A. Hwang. "Observations of Steep Wave Statistics in Open Ocean Waters." Journal of Atmospheric and Oceanic Technology 22, no. 3 (March 1, 2005): 258–71. http://dx.doi.org/10.1175/jtech1702.1.
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Abstract A new wavelet analysis methodology is proposed to estimate the statistics of steep waves. The method is applied to open ocean wave height data from the Southern Ocean Waves Experiment (1992) and from a field experiment conducted at Duck, North Carolina (1997). Results show that high wave slope crests appear over a wide range of wavenumbers, with a large amount being much shorter than the dominant wave. At low wave slope thresholds, all wave fields have roughly the same amount of wave crests regardless of wind forcing. The steep wave statistic decays exponentially with the square of the wave slope threshold, with a decay rate that is larger for the low wind cases than the high wind cases. Comparison of the steep wave statistic with independent measurements of the breaking wave statistic suggests a breaking wave slope threshold of about 0.12. The steep wave statistic does not scale with the cube of the wind speed, suggesting that other factors besides the wind speed also affect its level. Comparison of the steep wave statistic to the saturation spectrum reveals a reasonable correlation at moderate wave slope thresholds.
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Hernandez, C., P. Drobinski, S. Turquety, and J. L. Dupuy. "Size of wildfires in the Euro-Mediterranean region: observations and theoretical analysis." Natural Hazards and Earth System Sciences 15, no. 6 (June 23, 2015): 1331–41. http://dx.doi.org/10.5194/nhess-15-1331-2015.
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Abstract. MODIS (Moderate Resolution Imaging Spectroradiometer) satellite observations of fire size and ERA-Interim meteorological reanalysis are used to derive a relationship between burnt area and wind speed over the Mediterranean region and Eastern Europe. The largest wildfire size does not show a strong response with respect to wind speed in Eastern Europe. In the Mediterranean, as intuitively expected, the burnt area associated with the largest wildfires is an increasing function of wind speed for moderate temperature anomalies. In situations of severe heatwaves, the relationship between burnt area and wind speed displays a bimodal shape. Burnt areas are large for low 10 m wind speed (lower than 2 m s−1), decrease for moderate wind speed values (lower than 5 m s−1 and larger than 2 m s−1) and increase again for high wind speed (higher than 5 m s−1). To explain such behavior we use a stochastic model of fire propagation, known as a probabilistic cellular automata. This model uses a probabilistic local rule to derive the total burnt area. The observed relationship between burnt area and wind speed can be interpreted in terms of percolation threshold above which the propagation in the model is infinite, which mainly depends on local terrain slope and vegetation state (type, density, fuel moisture). In Eastern Europe, the percolation threshold is never exceeded for observed wind speeds. In the Mediterranean Basin we see two behaviors. During moderately hot weather, the percolation threshold is passed when the wind grows strong. On the other hand, in situations of severe Mediterranean heatwaves, moderate wind speed values impair the propagation of the wildfire against the wind and do not sufficiently accelerate the forward propagation to allow a growth of wildfire size.
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Fang, He, Tao Xie, William Perrie, Guosheng Zhang, Jingsong Yang, and Yijun He. "Comparison of C-Band Quad-Polarization Synthetic Aperture Radar Wind Retrieval Models." Remote Sensing 10, no. 9 (September 11, 2018): 1448. http://dx.doi.org/10.3390/rs10091448.
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This work discusses the accuracy of C-2PO (C-band cross-polarized ocean backscatter) and CMOD4 (C-band model) geophysical model functions (GMF) for sea surface wind speed retrieval from satellite-born Synthetic Aperture Radar (SAR) images over in the Northwest Pacific off the coast of China. In situ observations are used for comparison of the retrieved wind speed using two established wind retrieval models: C-2PO model and CMOD4 GMF. Using 439 samples from 92 RADARSAT-2 fine quad-polarization SAR images and corresponding reference winds, we created two subset wind speed databases: the training and testing subsets. From the training data subset, we retrieve ocean surface wind speeds (OSWSs) from different models at each polarization and compare with reference wind speeds. The RMSEs of SAR-retrieved wind speeds are: 2.5 m/s: 2.11 m/s (VH-polarized), 2.13 m/s (HV-polarized), 1.86 m/s (VV-polarized) and 2.26 m/s (HH-polarized) and the correlation coefficients are 0.86 (VH-polarized), 0.85(HV-polarized), 0.87(VV-polarized) and 0.83 (HH-polarized), which are statistically significant at the 99.9% significance level. Moreover, we found that OSWSs retrieved using C-2PO model at VH-polarized are most suitable for moderate-to-high winds while CMOD4 GMF at VV-polarized tend to be best for low-to-moderate winds. A hybrid wind retrieval model is put forward composed of the two models, C-2PO and CMOD4 and sets of SAR test data are used in order to establish an appropriate wind speed threshold, to differentiate the wind speed range appropriate for one model from that of the other. The results show that the OSWSs retrieved using our hybrid method has RMSE of 1.66 m/s and the correlation coefficient are 0.9, thereby significantly outperforming both the C-2PO and CMOD4 models.
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Fitch, Kyle E., Chaoxun Hang, Ahmad Talaei, and Timothy J. Garrett. "Arctic observations and numerical simulations of surface wind effects on Multi-Angle Snowflake Camera measurements." Atmospheric Measurement Techniques 14, no. 2 (February 12, 2021): 1127–42. http://dx.doi.org/10.5194/amt-14-1127-2021.
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Abstract. Ground-based measurements of frozen precipitation are heavily influenced by interactions of surface winds with gauge-shield geometry. The Multi-Angle Snowflake Camera (MASC), which photographs hydrometeors in free-fall from three different angles while simultaneously measuring their fall speed, has been used in the field at multiple midlatitude and polar locations both with and without wind shielding. Here, we present an analysis of Arctic field observations – with and without a Belfort double Alter shield – and compare the results to computational fluid dynamics (CFD) simulations of the airflow and corresponding particle trajectories around the unshielded MASC. MASC-measured fall speeds compare well with Ka-band Atmospheric Radiation Measurement (ARM) Zenith Radar (KAZR) mean Doppler velocities only when winds are light (≤5ms-1) and the MASC is shielded. MASC-measured fall speeds that do not match KAZR-measured velocities tend to fall below a threshold value that increases approximately linearly with wind speed but is generally <0.5ms-1. For those events with wind speeds ≤1.5ms-1, hydrometeors fall with an orientation angle mode of 12∘ from the horizontal plane, and large, low-density aggregates are as much as 5 times more likely to be observed. Simulations in the absence of a wind shield show a separation of flow at the upstream side of the instrument, with an upward velocity component just above the aperture, which decreases the mean particle fall speed by 55 % (74 %) for a wind speed of 5 m s−1 (10 m s−1). We conclude that accurate MASC observations of the microphysical, orientation, and fall speed characteristics of snow particles require shielding by a double wind fence and restriction of analysis to events where winds are light (≤5ms-1). Hydrometeors do not generally fall in still air, so adjustments to these properties' distributions within natural turbulence remain to be determined.
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Uhlhorn, Eric W., Peter G. Black, James L. Franklin, Mark Goodberlet, James Carswell, and Alan S. Goldstein. "Hurricane Surface Wind Measurements from an Operational Stepped Frequency Microwave Radiometer." Monthly Weather Review 135, no. 9 (September 1, 2007): 3070–85. http://dx.doi.org/10.1175/mwr3454.1.
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Abstract For the first time, the NOAA/Aircraft Operations Center (AOC) flew stepped frequency microwave radiometers (SFMRs) on both WP-3D research aircraft for operational hurricane surface wind speed measurement in 2005. An unprecedented number of major hurricanes provided ample data to evaluate both instrument performance and surface wind speed retrieval quality up to 70 m s−1 (Saffir–Simpson category 5). To this end, a new microwave emissivity–wind speed model function based on estimates of near-surface winds in hurricanes by global positioning system (GPS) dropwindsondes is proposed. For practical purposes, utilizing this function removes a previously documented high bias in moderate SFMR-measured wind speeds (10–50 m s−1), and additionally corrects an extreme wind speed (>60 m s−1) underestimate. The AOC operational SFMRs yield retrievals that are precise to within ∼2% at 30 m s−1, which is a factor of 2 improvement over the NOAA Hurricane Research Division’s SFMR, and comparable to the precision found here for GPS dropwindsonde near-surface wind speeds. A small (1.6 m s−1), but statistically significant, overall high bias was found for independent SFMR measurements utilizing emissivity data not used for model function development. Across the range of measured wind speeds (10–70 m s−1), SFMR 10-s averaged wind speeds are within 4 m s−1 (rms) of the dropwindsonde near-surface estimate, or 5%–25% depending on speed. However, an analysis of eyewall peak wind speeds indicates an overall 2.6 m s−1 GPS low bias relative to the peak SFMR estimate on the same flight leg, suggesting a real increase in the maximum wind speed estimate due to SFMR’s high-density sampling. Through a series of statistical tests, the SFMR is shown to reduce the overall bias in the peak surface wind speed estimate by ∼50% over the current flight-level wind reduction method and is comparable at extreme wind speeds. The updated model function is demonstrated to behave differently below and above the hurricane wind speed threshold (∼32 m s−1), which may have implications for air–sea momentum and kinetic energy exchange. The change in behavior is at least qualitatively consistent with recent laboratory and field results concerning the drag coefficient in high wind speed conditions, which show a fairly clear “leveling off” of the drag coefficient with increased wind speed above ∼30 m s−1. Finally, a composite analysis of historical data indicates that the earth-relative SFMR peak wind speed is typically located in the hurricane’s right-front quadrant, which is consistent with previous observational and theoretical studies of surface wind structure.
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Sun, Jielun, Larry Mahrt, Robert M. Banta, and Yelena L. Pichugina. "Turbulence Regimes and Turbulence Intermittency in the Stable Boundary Layer during CASES-99." Journal of the Atmospheric Sciences 69, no. 1 (January 1, 2012): 338–51. http://dx.doi.org/10.1175/jas-d-11-082.1.
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Abstract An investigation of nocturnal intermittent turbulence during the Cooperative Atmosphere–Surface Exchange Study in 1999 (CASES-99) revealed three turbulence regimes at each observation height: 1) regime 1, a weak turbulence regime when the wind speed is less than a threshold value; 2) regime 2, a strong turbulence regime when the wind speed exceeds the threshold value; and 3) regime 3, a moderate turbulence regime when top-down turbulence sporadically bursts into the otherwise weak turbulence regime. For regime 1, the strength of small turbulence eddies is correlated with local shear and weakly related to local stratification. For regime 2, the turbulence strength increases systematically with wind speed as a result of turbulence generation by the bulk shear, which scales with the observation height. The threshold wind speed marks the transition above which the boundary layer approaches near-neutral conditions, where the turbulent mixing substantially reduces the stratification and temperature fluctuations. The preference of the turbulence regimes during CASES-99 is closely related to the existence and the strength of low-level jets. Because of the different roles of the bulk and local shear with regard to turbulence generation under different wind conditions, the relationship between turbulence strength and the local gradient Richardson number varies for the different turbulence regimes. Turbulence intermittency at any observation height was categorized in three ways: turbulence magnitude oscillations between regimes 1 and 2 as wind speed varies back and forth across its threshold value, episodic turbulence enhancements within regime 1 as a result of local instability, and downbursts of turbulence in regime 3.
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Rakhmanov, R. S., D. A. Gadzhiibragimov, G. G. Bakhmydov, M. Kh Alikberov, and A. V. Tarasov. "ON THE EVALUATION OF WORKING CONDITIONS IN OPEN AREA IN THE WINTER SEASON." Hygiene and sanitation 98, no. 4 (October 28, 2019): 424–27. http://dx.doi.org/10.18821/0016-9900-2019-98-4-424-427.
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Introduction. The evaluation of the impact influence of weather and climatic conditions on humans in cold (winter) period was done since there was not the method of evaluation of working conditions according to the degree of harmfulness and danger. Also, the sanitary norms and rules 2.2.4.3359-16 does not contain the method of risk evaluation of the influence of factors upon the human organism. Мaterial and Methods. The authors evaluated the influence of various combinations of ambient temperature and wind speed upon under conditions of IV climatic region in I zone (the Republic of Dagestan - at an altitude of 4 m., 1040 m. and 1661 m above sea level and the Kaliningrad region) according to wind cooling. It was found a possible discomfort sensation at an average speed of winds and temperatures (wind cooling index (WCI) more 763,7 Kcal/m2) as well as overcooling risk in combinations of average temperature and maximum wind speed, an average speed of the wind and the minimum temperature. Maximum wind speeds in combination with minimal temperatures exceeded WCI threshold by 1,25-2,1 times. It should be noted that the studies were conducted under conditions of an increased humidity which had a negative influence upon the human organism, but in combination with the high wind speed and low temperatures, the effect might be more considerable. results. In accordance with the method, in attachment 17 in manual Р 2.2.2006-05, working conditions were classified as harmful. By calculation on indices of the minimal temperature and maximum wind speed, indices of equivalent temperatures reached up to considerable values. Probably, the use of the method does not prove its value. conclusion. The fixing of complex influence (in the cold period) of air velocity, ambient temperature, air humidity and detecting of health risk due to weather and climatic conditions remain a topical theoretical and practical problem.
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Wang, Qiang, Yunlong Zhu, and Kittipong Kasantikul. "A Novel Method for Ocean Wind Speed Detection Based on Energy Distribution of Beidou Reflections." Sensors 19, no. 12 (June 20, 2019): 2779. http://dx.doi.org/10.3390/s19122779.
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The Global Navigation Satellite System Reflectometry (GNSS-R) technique exploits the characteristics of reflected GNSS signals to estimate the geophysical parameters of the earth’s surface. This paper focuses on investigating the wind speed retrieval method using ocean scattered signals from a Beidou Geostationary Earth Orbit (GEO) satellite. Two new observables are proposed by computing the ratio of the low energy zone and the high energy zone of the delay waveform. Coastal experimental raw data from a Beidou GEO satellite are processed to establish the relationship between the energy-related observables and the sea surface wind. When the delay waveform normalized amplitude (this will be referred to as “threshold” in what follows) is 0.3, fitting results show that the coefficient of determination is more than 0.76 in the gentle wind scenario (<10 m/s), with a root mean square error (RMSE) of less than 1.0 m/s. In the Typhoon UTOR scenario (12.7 m/s~37.3 m/s), the correlation level exceeds 0.82 when the threshold is 0.25, with a RMSE of less than 3.10 m/s. Finally, the impact of the threshold and coherent integration time on wind speed retrieval is discussed to obtain an optimal result. When the coherent integration time is 50 milliseconds and the threshold is 0.15, the best wind speed retrieval error of 2.63 m/s and a correlation level of 0.871 are obtained in the UTOR scenario.
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Joslyn, Susan, Karla Pak, David Jones, John Pyles, and Earl Hunt. "The Effect of Probabilistic Information on Threshold Forecasts." Weather and Forecasting 22, no. 4 (August 1, 2007): 804–12. http://dx.doi.org/10.1175/waf1020.1.
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Abstract The study reported here asks whether the use of probabilistic information indicating forecast uncertainty improves the quality of deterministic weather decisions. Participants made realistic wind speed forecasts based on historical information in a controlled laboratory setting. They also decided whether it was appropriate to post an advisory for winds greater than 20 kt (10.29 m s−1) during the same time intervals and in the same geographic locations. On half of the forecasts each participant also read a color-coded chart showing the probability of winds greater than 20 kt. Participants had a general tendency to post too many advisories in the low probability situations (0%–10%) and too few advisories in very high probability situations (90%–100%). However, the probability product attenuated these biases. When participants used the probability product, they posted fewer advisories when the probability of high winds was low and they posted more advisories when the probability of high winds was high. The difference was due to the probability product alone because the within-subjects design and counterbalancing of forecast dates ruled out alternative explanations. The data suggest that the probability product improved threshold forecast decisions.
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Wang, Long, Cheng Chen, Tongguang Wang, and Weibin Wang. "Numerical Simulation of the Aeroelastic Response of Wind Turbines in Typhoons Based on the Mesoscale WRF Model." Sustainability 12, no. 1 (December 18, 2019): 34. http://dx.doi.org/10.3390/su12010034.
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A new simulation method for the aeroelastic response of wind turbines under typhoons is proposed. The mesoscale Weather Research and Forecasting (WRF) model was used to simulate a typhoon’s average wind speed field. The measured power spectrum and inverse Fourier transform method were coupled to simulate the pulsating wind speed field. Based on the modal method and beam theory, the wind turbine model was constructed, and the GH-BLADED commercial software package was used to calculate the aerodynamic load and aeroelastic response. The proposed method was applied to assess aeroelastic response characteristics of a commercial 6 MW offshore wind turbine under different wind speeds and direction variation patterns for the case study of typhoon Hagupit (2008), with a maximal wind speed of 230 km/h. The simulation results show that the typhoon’s average wind speed field and turbulence characteristics simulated by the proposed method are in good agreement with the measured values: Their difference in the main flow direction is only 1.7%. The scope of the wind turbine blade in the typhoon is significantly larger than under normal wind, while that under normal operation is higher than that under shutdown, even at low wind speeds. In addition, an abrupt change in wind direction has a significant impact on wind turbine response characteristics. Under normal operation, a sharp variation of the wind direction by 90 degrees in 6 s increases the wind turbine (WT) vibration scope by 27.9% in comparison with the case of permanent wind direction. In particular, the maximum deflection of the wind tower tip in the incoming flow direction reaches 28.4 m, which significantly exceeds the design standard safety threshold.
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Geldsetzer, Torsten, Shahid K. Khurshid, Kerri Warner, Filipe Botelho, and Dean Flett. "Wind Speed Retrieval from Simulated RADARSAT Constellation Mission Compact Polarimetry SAR Data for Marine Application." Remote Sensing 11, no. 14 (July 16, 2019): 1682. http://dx.doi.org/10.3390/rs11141682.
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RADARSAT Constellation Mission (RCM) compact polarimetry (CP) data were simulated using 504 RADARSAT-2 quad-pol SAR images. These images were used to samples CP data in three RCM modes to build a data set with co-located ocean wind vector observations from in situ buoys on the West and East coasts of Canada. Wind speeds up to 18 m/s were included. CP and linear polarization parameters were related to the C-band model (CMOD) geophysical model functions CMOD-IFR2 and CMOD5n. These were evaluated for their wind retrieval potential in each RCM mode. The CP parameter Conformity was investigated to establish a data-quality threshold (>0.2), to ensure high-quality data for model validation. An accuracy analysis shows that the first Stokes vector (SV0) and the right-transmit vertical-receive backscatter (RV) parameters were as good as the VV backscatter with CMOD inversion. SV0 produced wind speed retrieval accuracies between 2.13 m/s and 2.22 m/s, depending on the RCM mode. The RCM Medium Resolution 50 m mode produced the best results. The Low Resolution 100 m and Low Noise modes provided similar results. The efficacy of SV0 and RV imparts confidence in the continuity of robust wind speed retrieval with RCM CP data. Three image-based case studies illustrate the potential for the application of CP parameters and RCM modes in operational wind retrieval systems. The results of this study provide guidance to direct research objectives once RCM is launched. The results also provide guidance for operational RCM data implementation in Canada’s National SAR winds system, which provides near-real-time wind speed estimates to operational marine forecasters and meteorologists within Environment and Climate Change Canada.
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Splitt, Michael E., Steven M. Lazarus, Sarah Collins, Denis N. Botambekov, and William P. Roeder. "Probability Distributions and Threshold Selection for Monte Carlo–Type Tropical Cyclone Wind Speed Forecasts." Weather and Forecasting 29, no. 5 (October 1, 2014): 1155–68. http://dx.doi.org/10.1175/waf-d-13-00100.1.
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Abstract Probabilistic wind speed forecasts for tropical cyclones from Monte Carlo–type simulations are assessed within a theoretical framework for a simple unbiased Gaussian system that is based on feature size and location error that mimic tropical cyclone wind fields. Aspects of the wind speed probability data distribution, including maximum expected probability and forecast skill, are assessed. Wind speed probability distributions are shown to be well approximated by a bounded power-law distribution when the feature size is smaller than the location error and tends toward a U-shaped distribution as the location error becomes small. Forecast skill (i.e., true and Heidke skill scores) is shown to be highly dependent on the probability forecast data distribution. Forecasts from the National Hurricane Center (NHC) Wind Speed Probability Forecast Product are used to assess the applicability of the simple system in the interpretation and evaluation of a more advanced system.
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Rahdari, Mohammad Reza, and Andrés Rodríguez-Seijo. "Monitoring Sand Drift Potential and Sand Dune Mobility over the Last Three Decades (Khartouran Erg, Sabzevar, NE Iran)." Sustainability 13, no. 16 (August 12, 2021): 9050. http://dx.doi.org/10.3390/su13169050.
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Aeolian sediments cover about 6% of the earth’s surface, of which 97% occur in arid regions, and these sediments cover about 20% of the world’s lands. Sand drifts can harm sensitive ecosystems; therefore, this research has aimed to study wind regimes and the monitoring of sand drift potential and dune mobility in the Khartouran Erg (NE Iran). The study investigated 30 years of wind speed and direction to better understand sand dune mobility processes using the Fryberger and Tsoar methods. The results of the wind regime study showed that the eastern (33.4%) and northeastern (14.3%) directions were more frequent, but the study of winds greater than the threshold (6 m/s) in winter, spring, and autumn indicated the dominance of eastern and northern wind directions. Findings of calm winds showed that winters (40.4%) had the highest frequency, and summers (15%) had the lowest frequency; the annual frequency was 30%. The average wind speed in summers was the highest (4.38 m/s), and, in the winters, it was the lowest (2.28 m/s); the annual average wind speed was 3.3 m/s. The annual drift potential (DP = 173 VU) showed that it was categorized as low class, and the winds carried sand to the southwest. The monitoring of drift potential showed that there was a sharp increase between 2003 and 2008, which could have been attributed to a change in wind speeds in the region. Unite directional index, the index of directional variability, has been alternating from 0.3 to 0.6 for 30 years. Furthermore, monitoring of sand mobility recorded a value from 0.1 to 0.4, and the lowest and highest values were registered from 0.08 to 0.9, with an average of 0.27. Finally, it can be concluded that sand dunes have been fixed for a long time, and the intensity of the mobility index is affected by climate changes.
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Bjorkman, J. E. "The Wind-Compressed Disk Model." Symposium - International Astronomical Union 162 (1994): 455–68. http://dx.doi.org/10.1017/s0074180900215635.
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We discuss the effects of rotation on the structure of radiatively-driven winds. When the centrifugal support is large, there is a region, at low latitudes near the surface of the star, where the acceleration of gravity is larger than the radiative acceleration. Within this region, the fluid streamlines “fall” toward the equator. If the rotation rate is large, this region is big enough that the fluid from the northern hemisphere collides with that from the southern hemisphere. This produces standing shocks above and below the equator. Between the shocks, there is a dense equatorial disk that is confined by the ram pressure of the wind. A portion of the flow that enters the disk proceeds outward along the equator, but the inner portion accretes onto the stellar surface. Thus there is simultaneous outflow and infall in the equatorial disk. The wind-compressed disk forms only if the star is rotating faster than a threshold value, which depends on the ratio of wind terminal speed to stellar escape speed. The spectral type dependence of the disk formation threshold may explain the frequency distribution of Be stars. Observational tests of the wind-compressed disk model indicate that, although the geometry of the disk agrees with observations of Be stars, the density is a factor of 100 too small to produce the IR excess, Hα emission, and optical polarization, if current estimates of the mass-loss rates are used. However, recent calculations of the ionization balance in the wind indicate that the mass-loss rates of Be stars may be significantly underestimated.
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CREYSSELS, M., P. DUPONT, A. OULD EL MOCTAR, A. VALANCE, I. CANTAT, J. T. JENKINS, J. M. PASINI, and K. R. RASMUSSEN. "Saltating particles in a turbulent boundary layer: experiment and theory." Journal of Fluid Mechanics 625 (April 14, 2009): 47–74. http://dx.doi.org/10.1017/s0022112008005491.
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The work presented here focuses on the analysis of a turbulent boundary layer saturated with saltating particles. Experiments were carried out in a wind tunnel 15m long and 0.6m wide at the University of Aarhus in Denmark with sand grains 242 μm in size for wind speeds ranging from the threshold speed to twice its value. The saltating particles were analysed using particle image velocimetry (PIV) and particle-tracking velocimetry (PTV), and vertical profiles of particle concentration and velocity were extracted. The particle concentration was found to decrease exponentially with the height above the bed, and the characteristic decay height was independent of the wind speed. In contrast with the logarithmic profile of the wind speed, the grain velocity was found to vary linearly with the height. In addition, the measurements indicated that the grain velocity profile depended only slightly on the wind speed. These results are shown to be closely related to the features of the splash function that characterizes the impact of the saltating particles on a sandbed. A numerical simulation is developed that explicitly incorporates low-velocity moments of the splash function in a calculation of the boundary conditions that apply at the bed. The overall features of the experimental measurements are reproduced by simulation.
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Kirkwood, S., A. Osepian, E. Belova, and Y. S. Lee. "High-speed solar wind streams and polar mesosphere winter echoes at Troll, Antarctica." Annales Geophysicae 33, no. 6 (June 1, 2015): 609–22. http://dx.doi.org/10.5194/angeo-33-609-2015.
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Abstract. A small, 54 MHz wind-profiler radar, MARA, was operated at Troll, Antarctica (72° S, 2.5° E), continuously from November 2011 to January 2014, covering two complete Antarctic winters. Despite very low power, MARA observed echoes from heights of 55–80 km (polar mesosphere winter echoes, PMWE) on 60% of all winter days (from March to October). This contrasts with previous reports from radars at high northern latitudes, where PWME have been reported only by very high power radars or during rare periods of unusually high electron density at PMWE heights, such as during solar proton events. Analysis shows that PWME at Troll were not related to solar proton events but were often closely related to the arrival of high-speed solar wind streams (HSS) at the Earth, with PWME appearing at heights as low as 56 km and persisting for up to 15 days following HSS arrival. This demonstrates that HSS effects penetrate directly to below 60 km height in the polar atmosphere. Using local observations of cosmic-noise absorption (CNA), a theoretical ionization/ion-chemistry model and a statistical model of precipitating energetic electrons associated with HSS, the electron density conditions during the HSS events are estimated. We find that PMWE detectability cannot be explained by these variations in electron density and molecular-ion chemistry alone. PWME become detectable at different thresholds depending on solar illumination and height. In darkness, PWME are detected only when the modelled electron density is above a threshold of about 1000 cm−3, and only above 75 km height, where negative ions are few. In daylight, the electron density threshold falls by at least 2 orders of magnitude and PWME are found primarily below 75 km height, even in conditions when a large proportion of negative ions is expected. There is also a strong dawn–dusk asymmetry with PWME detected very rarely during morning twilight but often during evening twilight. This behaviour cannot be explained if PMWE are caused by small-scale structure in the neutral/molecular-ion gas alone but may be explained by the presence of charged meteoric dust.
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Eldridge, D. J., and J. F. Leys. "Wind Dispersal of the Vagant Lichen Chondropsis semiviridis in Semi-arid Eastern Australia." Australian Journal of Botany 47, no. 2 (1999): 157. http://dx.doi.org/10.1071/bt97073.
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A field-based wind tunnel was used to assess threshold wind velocities required to initiate movement of the vagant lichen Chondropsis semiviridis (F.Muell. ex Nyl.) Nyl. in a semi-arid eastern Australian woodland. Threshold wind velocities were lowest on bare surfaces (21 km h-1) and highest on surfaces covered with the needle-like litter of Casuarina cristata Miq. trees (58 km h-1). Examination of wind speed data suggests that threshold wind velocities for movement on litter-covered surfaces occur about 1% of the time in summer. The extensive litter cover in the groves, and the tendency of C. semiviridis to firmly attach to this litter, probably explains the concentration of C. semiviridis in the groves and the low rates of migration and emigration during most years. It is hypothesised that migration of C. semiviridis between timbered groves would only occur during extreme droughts when pasture and litter cover are sparse.
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Parvin, Nader, Emam Ali Asheri, Ebrahim Mesgari, and Abdolla Ahmadi. "The Spatial Distribution of Atmospheric Conditions, Severe Storms Zab Basin in Iran (A Case Study of Cut off Low Synoptic Pattern)." International Letters of Social and Humanistic Sciences 61 (October 2015): 39–45. http://dx.doi.org/10.18052/www.scipress.com/ilshs.61.39.
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Atmospheric circulation patterns is the most important method of identification of environmental change that, it is useful For purposes such as weather forecasting, predict natural events (air pollution, floods, drought, etc). The aim of this study is to analyze the synoptic conditions of severe storms is Zab basin. Daily data of wind speed over the period 1364/01/01 to 1390/12/29 of three synoptic stations was taken from the department of meteorology. Given the scale of temporal and spatial distribution, wind speed and comprehensiveness of the three threshold size and calculate the 90th percentile wind speed, 40 days pervasive and severe storms were selected. Sea level pressure data on the network with a size 5.2°*5.2° that was located on Cornell 0-80 degrees east longitude and 0-80 degrees northern latitude from the database NCEP/NCAR were extracted. Matrix was formed in the dimensions of 40*864 with storm was on the rows and elevation data middle levels of the atmosphere, was on the columns. A principal component analysis was performed on data matrix elevation and six factors were identified that about 97.4% of the Pressure elevation changes of 500hp level was explained. To identify synoptic patterns, cluster analysis integration "ward's" was performed on these components.The results showed that, Cut off low synoptic pattern of the upper atmosphere with an abundance of 47.5% in May and December had the highest frequency. Irregularities in the movement and position of the polar vortex caused the jet stream and storm paths meridional winds greater control and troughs are driven towards the low latitudes deeper. As a result, the pressure gradient and energy exchange at its maximum reached compression Isobaric lines and Strong winds in the catchment area level has been created. All patterns are identified for the winds mainly from the west and southwest.
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Earl, Nick, Steve Dorling, Richard Hewston, and Roland von Glasow. "1980–2010 Variability in U.K. Surface Wind Climate." Journal of Climate 26, no. 4 (February 15, 2013): 1172–91. http://dx.doi.org/10.1175/jcli-d-12-00026.1.
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Abstract The climate of the northeast Atlantic region comprises substantial decadal variability in storminess. It also exhibits strong inter- and intra-annual variability in extreme high and low wind speed episodes. Here the authors quantify and discuss causes of the variability seen in the U.K. wind climate over the recent period 1980–2010. Variations in U.K. hourly mean (HM) wind speeds, in daily maximum gust speeds and in associated wind direction measurements, made at standard 10-m height and recorded across a network of 40 stations, are considered. The Weibull distribution is shown to generally provide a good fit to the hourly wind data, albeit with the shape parameter k spatially varying from 1.4 to 2.1, highlighting that the commonly assumed k = 2 Rayleigh distribution is not universal. It is found that the 10th and 50th percentile HM wind speeds have declined significantly over this specific period, while still incorporating a peak in the early 1990s. The authors' analyses place the particularly “low wind” year of 2010 into longer-term context and their findings are compared with other recent international studies. Wind variability is also quantified and discussed in terms of variations in the exceedance of key wind speed thresholds of relevance to the insurance and wind energy industries. Associated interannual variability in energy density and potential wind power output of the order of ±20% around the mean is revealed. While 40% of network average winds are in the southwest quadrant, 51% of energy in the wind is associated with this sector. The findings are discussed in the context of current existing challenges to improve predictability in the Euro-Atlantic sector over all time scales.
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Van de Wiel, B. J. H., A. F. Moene, H. J. J. Jonker, P. Baas, S. Basu, J. M. M. Donda, J. Sun, and A. A. M. Holtslag. "The Minimum Wind Speed for Sustainable Turbulence in the Nocturnal Boundary Layer." Journal of the Atmospheric Sciences 69, no. 11 (November 1, 2012): 3116–27. http://dx.doi.org/10.1175/jas-d-12-0107.1.
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Abstract The collapse of turbulence in the nocturnal boundary layer is studied by means of a simple bulk model that describes the basic physical interactions in the surface energy balance. It is shown that for a given mechanical forcing, the amount of turbulent heat that can be transported downward is limited to a certain maximum. In the case of weak winds and clear skies, this maximum can be significantly smaller than the net radiative loss minus soil heat transport. In the case when the surface has low heat capacity, this imbalance generates rapid surface cooling that further suppresses the turbulent heat transport, so that eventually turbulence largely ceases (positive feedback mechanism). The model predicts the minimum wind speed for sustainable turbulence for the so-called crossing level. At this level, some decameters above the surface, the wind is relatively stationary compared to lower and higher levels. The critical speed is predicted in the range of about 5–7 m s−1, depending on radiative forcing and surface properties, and is in agreement with observations at Cabauw. The critical value appears not very sensitive to model details or to the exact values of the input parameters. Finally, results are interpreted in terms of external forcings, such as geostrophic wind. As it is generally larger than the speed at crossing height, a 5 m s−1 geostrophic wind may be considered as the typical limit below which sustainable, continuous turbulence under clear-sky conditions is unlikely to exist. Below this threshold emergence of the very stable nocturnal boundary layer is anticipated.
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Saleem, Rana Muhammad, Rafaqat Kazmi, Imran Sarwar Bajwa, Amna Ashraf, Shabana Ramzan, and Waheed Anwar. "IOT-Based Cotton Whitefly Prediction Using Deep Learning." Scientific Programming 2021 (July 10, 2021): 1–17. http://dx.doi.org/10.1155/2021/8824601.
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Agriculture is suffering from the problem of low fertility and climate hazards such as increased pest attacks and diseases. Early prediction of pest attacks can be very helpful in improving productivity in agriculture. Insect pest (whitefly) attack has a high influence on cotton crop yield. Internet of Things solution is proposed to predict the whitefly attack to take prevention measures. An insect pest prediction system (IPPS) was developed with the help of the Internet of Things and a RBFN algorithm based on environmental parameters such as temperature, humidity, rainfall, and wind speed. Pest Warning and Quality Control of Pesticides proposed an economic threshold level for prediction of whitefly attack. The economic threshold level and RBFN algorithm are used to predict the whitefly attack using temperature, humidity, rainfall, and wind speed. The seven evaluation metrics accuracy, f-measures, precision, recall, Cohen’s kappa, ROC AUC, and confusion matrix are used to determine the performance of the RBFN algorithm. The proposed insect pest prediction system is deployed in the high influenced region of pest that provides pest prediction information to the farmer to take control measures.
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Genthon, Christophe, Delphine Six, Vincent Favier, Matthew Lazzara, and Linda Keller. "Atmospheric Temperature Measurement Biases on the Antarctic Plateau." Journal of Atmospheric and Oceanic Technology 28, no. 12 (December 1, 2011): 1598–605. http://dx.doi.org/10.1175/jtech-d-11-00095.1.
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Abstract Observations of atmospheric temperature made on the Antarctic Plateau with thermistors housed in naturally (wind) ventilated radiation shields are shown to be significantly warm biased by solar radiation. High incoming solar flux and high surface albedo result in radiation biases in Gill (multiplate)-styled shields that can occasionally exceed 10°C in summer in cases with low wind speed. Although stronger and more frequent when incoming solar radiation is high, biases exceeding 8°C are found even when solar radiation is less than 200 W m−2. Compared with sonic thermometers, which are not affected by radiation but are too complex to be routinely used for mean temperature monitoring, commercially available aspirated shields are shown to efficiently protect thermistor measurements from solar radiation biases. Most of the available in situ reports of atmospheric temperature on the Antarctic Plateau are from automatic weather stations that use passive shields and are thus likely warm biased in the summer. In spite of low power consumption, deploying aspirated shields at remote locations in such a difficult environment may be a challenge. Bias correction formulas are not easily derived and are obviously shield dependent. On the other hand, because of a strong dependence of bias to wind speed, filtering out temperature reports for wind speed less than a given threshold (about 4–6 m s−1 for the shields tested here) may be an efficient way to quality control the data, albeit at the cost of significant data loss and records that are biased toward high wind speed cases.
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Gierach, Michelle M., Mark A. Bourassa, Philip Cunningham, James J. O’Brien, and Paul D. Reasor. "Vorticity-Based Detection of Tropical Cyclogenesis." Journal of Applied Meteorology and Climatology 46, no. 8 (August 1, 2007): 1214–29. http://dx.doi.org/10.1175/jam2522.1.
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Abstract Ocean wind vectors from the SeaWinds scatterometer aboard the Quick Scatterometer (QuikSCAT) satellite and Geostationary Operational Environmental Satellite (GOES) imagery are used to develop an objective technique that can detect and monitor tropical disturbances associated with the early stages of tropical cyclogenesis in the Atlantic basin. The technique is based on identification of surface vorticity and wind speed signatures that exceed certain threshold magnitudes, with vorticity averaged over an appropriate spatial scale. The threshold values applied herein are determined from the precursors of 15 tropical cyclones during the 1999–2004 Atlantic Ocean hurricane seasons using research-quality QuikSCAT data. The choice of these thresholds is complicated by the lack of suitable validation data. The combination of GOES and QuikSCAT data is used to track the tropical disturbances that are precursors to the 15 tropical cyclones. This combination of data can be used to test detection but is not as easily used to examine false alarms. Tropical disturbances are found for these cases within a range of 19–101 h before classification as tropical cyclones by the National Hurricane Center. The 15 cases are further subdivided based upon their origination source (i.e., easterly wave, upper-level cutoff low, stagnant frontal zone, etc.). The primary focus centers on the cases associated with tropical waves, because these waves account for the majority of all Atlantic tropical cyclones. The detection technique illustrates the ability to track these tropical disturbances from near the coast of Africa. Analysis of the pretropical cyclone (pre-TC) tracks for these cases depicts stages, related to wind speed and precipitation, in the evolution of a tropical disturbance within an easterly wave to a tropical cyclone.
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Fors, Ane S., Dmitry V. Divine, Anthony P. Doulgeris, Angelika H. H. Renner, and Sebastian Gerland. "Signature of Arctic first-year ice melt pond fraction in X-band SAR imagery." Cryosphere 11, no. 2 (March 23, 2017): 755–71. http://dx.doi.org/10.5194/tc-11-755-2017.
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Abstract. In this paper we investigate the potential of melt pond fraction retrieval from X-band polarimetric synthetic aperture radar (SAR) on drifting first-year sea ice. Melt pond fractions retrieved from a helicopter-borne camera system were compared to polarimetric features extracted from four dual-polarimetric X-band SAR scenes, revealing significant relationships. The correlations were strongly dependent on wind speed and SAR incidence angle. Co-polarisation ratio was found to be the most promising SAR feature for melt pond fraction estimation at intermediate wind speeds (6. 2 m s−1), with a Spearman's correlation coefficient of 0. 46. At low wind speeds (0. 6 m s−1), this relation disappeared due to low backscatter from the melt ponds, and backscatter VV-polarisation intensity had the strongest relationship to melt pond fraction with a correlation coefficient of −0. 53. To further investigate these relations, regression fits were made both for the intermediate (R2fit = 0. 21) and low (R2fit = 0. 26) wind case, and the fits were tested on the satellite scenes in the study. The regression fits gave good estimates of mean melt pond fraction for the full satellite scenes, with less than 4 % from a similar statistics derived from analysis of low-altitude imagery captured during helicopter ice-survey flights in the study area. A smoothing window of 51 × 51 pixels gave the best reproduction of the width of the melt pond fraction distribution. A considerable part of the backscatter signal was below the noise floor at SAR incidence angles above ∼ 40°, restricting the information gain from polarimetric features above this threshold. Compared to previous studies in C-band, limitations concerning wind speed and noise floor set stricter constraints on melt pond fraction retrieval in X-band. Despite this, our findings suggest new possibilities in melt pond fraction estimation from X-band SAR, opening for expanded monitoring of melt ponds during melt season in the future.
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Cowie, S. M., P. Knippertz, and J. H. Marsham. "A climatology of dust emission events from northern Africa using long-term surface observations." Atmospheric Chemistry and Physics Discussions 14, no. 6 (March 18, 2014): 7425–68. http://dx.doi.org/10.5194/acpd-14-7425-2014.
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Abstract. Long-term (1984–2012) surface observations from 70 stations in the Sahara and Sahel are used to explore the diurnal, seasonal and geographical variations in dust emission events and thresholds. The frequency of dust emission (FDE) is calculated using the present weather codes of SYNOP reports. Thresholds are estimated as the wind speed for which there is a 50% probability of dust emission and are then used to calculate strong wind frequency (SWF) and dust uplift potential (DUP), where the latter is an estimate of the dust-generating power of winds. Stations are grouped into six coherent geographical areas for more in-depth analysis. FDE is highest at stations in Sudan and overall peaks in spring north of 23° N. South of this, where stations are directly influenced by the summer monsoon, the annual cycle in FDE is more variable. Thresholds are highest in northern Algeria, lowest in the latitude band 16–21° N and have greatest seasonal variations in the Sahel. Spatial variability in thresholds partly explain spatial variability in frequency of dust emission events on an annual basis. However, seasonal variations in thresholds for the six grouped areas are not the main control on seasonal variations in FDE. This is demonstrated by highly correlated seasonal cycles of FDE and SWF which are not significantly changed by using a fixed, or seasonally varying, threshold. The likely meteorological mechanisms generating these patterns such as low-level jets and haboobs are discussed.
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Cowie, S. M., P. Knippertz, and J. H. Marsham. "A climatology of dust emission events from northern Africa using long-term surface observations." Atmospheric Chemistry and Physics 14, no. 16 (August 25, 2014): 8579–97. http://dx.doi.org/10.5194/acp-14-8579-2014.
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Abstract. Long-term (1984–2012) surface observations from 70 stations in the Sahara and Sahel are used to explore the diurnal, seasonal and geographical variations in dust emission events and thresholds. The frequency of dust emission (FDE) is calculated using the present weather codes of SYNOP reports. Thresholds are estimated as the wind speed for which there is a 50% probability of dust emission and are then used to calculate strong wind frequency (SWF) and dust uplift potential (DUP), where the latter is an estimate of the dust-generating power of winds. Stations are grouped into six coherent geographical areas for more in-depth analysis. FDE is highest at stations in Sudan and overall peaks in spring north of 23° N. South of this, where stations are directly influenced by the summer monsoon, the annual cycle in FDE is more variable. Thresholds are highest in northern Algeria, lowest in the latitude band 16–21° N and have greatest seasonal variations in the Sahel. Spatial variability in thresholds partly explain spatial variability in frequency of dust emission events on an annual basis. However, seasonal variations in thresholds for the six grouped areas are not the main control on seasonal variations in FDE. This is demonstrated by highly correlated seasonal cycles of FDE and SWF which are not significantly changed by using a fixed, or seasonally varying, threshold. The likely meteorological mechanisms generating these patterns such as low-level jets and haboobs are discussed.
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Andreotti, Bruno, Philippe Claudin, Jens Jacob Iversen, Jonathan P. Merrison, and Keld R. Rasmussen. "A lower-than-expected saltation threshold at Martian pressure and below." Proceedings of the National Academy of Sciences 118, no. 5 (January 28, 2021): e2012386118. http://dx.doi.org/10.1073/pnas.2012386118.
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Aeolian sediment transport is observed to occur on Mars as well as other extraterrestrial environments, generating ripples and dunes as on Earth. The search for terrestrial analogs of planetary bedforms, as well as environmental simulation experiments able to reproduce their formation in planetary conditions, are powerful ways to question our understanding of geomorphological processes toward unusual environmental conditions. Here, we perform sediment transport laboratory experiments in a closed-circuit wind tunnel placed in a vacuum chamber and operated at extremely low pressures to show that Martian conditions belong to a previously unexplored saltation regime. The threshold wind speed required to initiate saltation is only quantitatively predicted by state-of-the art models up to a density ratio between grain and air of4×105but unexpectedly falls to much lower values for higher density ratios. In contrast, impact ripples, whose emergence is continuously observed on the granular bed over the whole pressure range investigated, display a characteristic wavelength and propagation velocity essentially independent of pressure. A comparison of these findings with existing models suggests that sediment transport at low Reynolds number but high grain-to-fluid density ratio may be dominated by collective effects associated with grain inertia in the granular collisional layer.
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Zhang, Hanbing, Yang Gao, Danfeng Sun, Lulu Liu, Yanzhi Cui, and Wenjie Zhu. "Wind Erosion Changes in a Semi-Arid Sandy Area, Inner Mongolia, China." Sustainability 11, no. 1 (January 1, 2019): 188. http://dx.doi.org/10.3390/su11010188.
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Wind erosion is one of the major environmental problems in drylands. Identifying the dominant natural factors of wind erosion and using targeted treatment measures are the key steps in wind erosion control. Using Horqin Left Back Banner in China as a case study, we applied the revised wind erosion equation to simulate the spatial distribution of wind erosion in the semi-arid sandy area. Contribution assessment and constraint line analysis were used to investigate the contributions of driving forces to wind erosion changes. The results showed that the wind erosion in the whole area was reduced by 0.35 t/hm2·a from 2005 to 2016. The wind factor and vegetation coverage factor had dominant contributions to the wind erosion modulus and accounted for the erosion in 49.87% and 50.13% of the total area, respectively. In addition, the average wind speed exceeding the threshold and the number of occurrences exhibited significant correlations with the wind erosion severity. Meanwhile, the mitigation effects of vegetation coverage on wind erosion decreased with the increase in wind speed. The temporal mismatch between the wind speed and vegetation coverage was the main reason for the frequent severe wind erosion in spring. Reducing the spring wind speed through adding windbreaks would be an effective method for decreasing wind erosion in semi-arid areas.
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Coffer, Brice E., and Matthew D. Parker. "Simulated Supercells in Nontornadic and Tornadic VORTEX2 Environments." Monthly Weather Review 145, no. 1 (December 16, 2016): 149–80. http://dx.doi.org/10.1175/mwr-d-16-0226.1.
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Abstract The composite near-storm environments of nontornadic and tornadic supercells sampled during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) both appear to be generally favorable for supercells and tornadoes. It has not been clear whether small differences between the two environments (e.g., more streamwise horizontal vorticity in the lowest few hundred meters above the ground in the tornadic composite) are actually determinative of storms’ tornadic potential. From the VORTEX2 composite environments, simulations of a nontornadic and a tornadic supercell are used to investigate storm-scale differences that ultimately favor tornadogenesis or tornadogenesis failure. Both environments produce strong supercells with robust midlevel mesocyclones and hook echoes, though the tornadic supercell has a more intense low-level updraft and develops a tornado-like vortex exceeding the EF3 wind speed threshold. In contrast, the nontornadic supercell only produces shallow vortices, which never reach the EF0 wind speed threshold. Even though the nontornadic supercell readily produces subtornadic surface vortices, these vortices fail to be stretched by the low-level updraft. This is due to a disorganized low-level mesocyclone caused by predominately crosswise vorticity in the lowest few hundred meters above ground level within the nontornadic environment. In contrast, the tornadic supercell ingests predominately streamwise horizontal vorticity, which promotes a strong low-level mesocyclone with enhanced dynamic lifting and stretching of surface vertical vorticity. These results support the idea that larger streamwise vorticity leads to a more intense low-level mesocyclone, whereas predominately crosswise vorticity yields a less favorable configuration of the low-level mesocyclone for tornadogenesis.
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Ruel, J. C., S. Meunier, C. P. Quine, and J. Suarez. "Estimating windthrow risk in balsam fir stands with the ForestGales model." Forestry Chronicle 76, no. 2 (April 1, 2000): 329–37. http://dx.doi.org/10.5558/tfc76329-2.
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Balsam fir (Abies balsamea (L.) Mill.) forests are inherently vulnerable to windthrow, especially when silvicultural treatments are applied. During recent years, it has become possible to model windthrow risk based on a good understanding of windthrow mechanics. In the present paper, the British ForestGales model has been adapted for balsam fir with data from a winching study in Quebec, Canada. This model calculates the threshold wind speed required to break or overturn the average tree in a stand and then calculates the probability of exceeding the threshold value. Modifications of the equations predicting crown characteristics and overturning resistance were introduced. The effects of age, site quality, wind exposure, thinning and the creation of new edges were assessed. The estimated critical wind speed for overturning and breakage decreases with age but the probability of damage remains low on sheltered sites. The creation of a new edge leads to an increased probability of damage, especially on exposed, highly productive sites. Thinning alone also increases the probability of damage and the magnitude of the increase varies with age and thinning intensity. On highly productive sheltered sites, the effect of thinning becomes especially important when thinning exceeds 35% of the number of stems or when stand age is greater than 70 years for a 35% thinning intensity. Thinning of new edges was also found to further increase the risk of windthrow on the most sheltered, high quality sites.
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Reed, Kevin A., and Christiane Jablonowski. "An Analytic Vortex Initialization Technique for Idealized Tropical Cyclone Studies in AGCMs." Monthly Weather Review 139, no. 2 (February 1, 2011): 689–710. http://dx.doi.org/10.1175/2010mwr3488.1.
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Abstract The paper discusses the design of idealized tropical cyclone experiments in atmospheric general circulation models (AGCMs). The evolution of an initially weak, warm-core vortex is investigated over a 10-day period with varying initial conditions that include variations of the maximum wind speed and radius of maximum wind. The initialization of the vortex is built upon prescribed 3D moisture, pressure, temperature, and velocity fields that are embedded into tropical environmental conditions. The initial fields are in exact hydrostatic and gradient-wind balance in an axisymmetric form. The formulation is then generalized to provide analytic initial conditions for an approximately balanced vortex in AGCMs with height-based vertical coordinates. An extension for global models with pressure-based vertical coordinates is presented. The analytic initialization technique can easily be implemented on any AGCM computational grid. The characteristics of the idealized tropical cyclone experiments are illustrated in high-resolution model simulations with the Community Atmosphere Model version 3.1 (CAM 3.1) developed at the National Center for Atmospheric Research. The finite-volume dynamical core in CAM 3.1 with 26 vertical levels is used, and utilizes an aquaplanet configuration with constant sea surface temperatures of 29°C. The impact of varying initial conditions and horizontal resolutions on the evolution of the tropical cyclone–like vortex is investigated. Identical physical parameterizations with a constant parameter set are used at all horizontal resolutions. The sensitivity studies reveal that the initial wind speed and radius of maximum wind need to lie above a threshold to support the intensification of the analytic initial vortex at horizontal grid spacings of 0.5° and 0.25° (or 55 and 28 km in the equatorial regions). The thresholds lie between 15 and 20 m s−1 with a radius of maximum wind of about 200–250 km. In addition, a convergence study with the grid spacings 1.0°, 0.5°, 0.25°, and 0.125° (or 111, 55, 28, and 14 km) shows that the cyclone gets more intense and compact with increasing horizontal resolution. The 0.5°, 0.25°, and 0.125° simulations exhibit many tropical cyclone–like characteristics such as a warm-core, low-level wind maxima, a slanted eyewall-like vertical structure and a relatively calm eye. The 0.125° simulation even starts to resolve spiral rainbands and reaches maximum wind speeds of about 72–83 m s−1 at low levels. These wind speeds are equivalent to a category-5 tropical cyclone on the Saffir–Simpson hurricane scale. It is suggested that the vortex initialization technique can be used as an idealized tool to study the impact of varying resolutions, physical parameterizations, and numerical schemes on the simulation and representation of tropical cyclone–like vortices in global atmospheric models.
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Brantley, Halley, Gayle Hagler, Scott Herndon, Paola Massoli, Michael Bergin, and Armistead Russell. "Characterization of Spatial Air Pollution Patterns Near a Large Railyard Area in Atlanta, Georgia." International Journal of Environmental Research and Public Health 16, no. 4 (February 13, 2019): 535. http://dx.doi.org/10.3390/ijerph16040535.
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Railyards are important transportation hubs, and they are often situated near populated areas with high co-located density of manufacturing, freight movement and commercial enterprises. Emissions occurring within railyards can affect nearby air quality. To better understand the air pollution levels in proximity to a major railyard, an intensive mobile air monitoring study was conducted in May 2012 around a major railyard area in Atlanta, GA, constituted of two separate facilities situated side-by-side. A total of 19 multi-hour mobile monitoring sessions took place over different times of day, days of the week, and under a variety of wind conditions. High time resolution measurements included black carbon (BC), particle number concentration (PN), particle optical extinction (EXT), oxides of nitrogen (NO, NO2, NOy), carbon monoxide (CO), and speciated air toxics. Urban background was estimated to contribute substantially (>70%) to EXT and CO, whereas BC, oxides of nitrogen (NOx) and toluene had comparably low background contributions (<30%). Mobile monitoring data were aggregated into 50 meter spatial medians by wind categories, with categories including low speed wind conditions (<0.5 m s−1) and, for wind speeds above that threshold, by wind direction relative to the railyard. Spatial medians of different pollutants measured had a wide range of correlation—gas-phase air toxics (benzene, toluene, acetaldehyde) had moderate correlation with each other (r = 0.46–0.59) and between toluene and CO (r = 0.53), but lower correlation for other pairings. PN had highest correlation with oxides of nitrogen (r = 0.55–0.66), followed by BC (r = 0.4), and lower correlation with other pollutants. Multivariate regression analysis on the full set of 50 m medians found BC and NO as having the strongest relationship to railyard emissions, in comparison to their respective background levels. This was indicated by an increase associated with transiting through the yard and inverse relationship with distance from the railyard; NO and BC decreased by a factor of approximately 0.5 and 0.7 over 1 km distance of the railyard boundary, respectively. Low speed, variable wind conditions were related to higher concentrations of all measured parameters.
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Berg, T., K. A. Pfaffhuber, A. S. Cole, O. Engelsen, and A. Steffen. "Ten years trends in atmospheric mercury concentrations, meteorological effects and climate variables at Zeppelin, Ny-Ålesund." Atmospheric Chemistry and Physics Discussions 13, no. 1 (January 22, 2013): 2273–312. http://dx.doi.org/10.5194/acpd-13-2273-2013.
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Abstract. Results from ten years of gaseous elemental mercury (GEM) measurements at Zeppelin Station, Ny-Ålesund, Svalbard, show no overall annual trend between 2000 and 2009. Seasonal trend analysis showed significantly decreasing trends in January, February, March and June and significantly increasing trends in May and July through December. Results showed that atmospheric mercury depletion events (AMDEs) were equally distributed between April and May with only a few having been observed in March and June. A negative correlation between AMDEs and temperature is reported and supports earlier observations that AMDEs tend to occur at low temperatures. Lower concentrations of GEM were seen at lower temperatures below a threshold of 0°C. The occurrence of AMDEs and wind direction were well correlated with the lowest GEM measured when the wind direction was from the Arctic Ocean region. Wind speed was found to not correlate with AMDEs, but the lowest GEM concentrations were observed at low wind speeds between 4 and 11 m s−1. AMDEs and relative humidity did not correlate well, but the lowest GEM levels appeared when the relative humidity was between 80 and 90%. Diurnal variation was observed especially during the month March and is likley due to daytime snow surface emission induced by solar radiation. Relationships between GEM concentration and the Northern Hemisphere climate indices were investigated to assess if these climate parameters might reflect different atmospheric conditions that enhance or reduce spring AMDE activity. No consistent pattern was observed.
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Kukulka, Tobias, and Tetsu Hara. "The Effect of Breaking Waves on a Coupled Model of Wind and Ocean Surface Waves. Part I: Mature Seas." Journal of Physical Oceanography 38, no. 10 (October 1, 2008): 2145–63. http://dx.doi.org/10.1175/2008jpo3961.1.
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Abstract This is the first of a two-part investigation of a coupled wind and wave model that includes the enhanced form drag of breaking waves. In Part I here the model is developed and applied to mature seas. Part II explores the solutions in a wide range of wind and wave conditions, including growing seas. Breaking and nonbreaking waves induce air-side fluxes of momentum and energy above the air–sea interface. By balancing air-side momentum and energy and by conserving wave energy, coupled nonlinear advance–delay differential equations are derived, which govern simultaneously the wave and wind field. The system of equations is closed by introducing a relation between the wave height spectrum and wave dissipation due to breaking. The wave dissipation is proportional to nonlinear wave interactions, if the wave curvature spectrum is below the “threshold saturation level.” Above this threshold the wave dissipation rapidly increases so that the wave height spectrum is limited. The coupled model is applied to mature wind-driven seas for which the wind forcing only occurs in the equilibrium range away from the spectral peak. Modeled wave height curvature spectra as functions of wavenumber k are consistent with observations and transition from k1/2 at low wavenumbers to k0 at high wavenumbers. Breaking waves affect only weakly the wave height spectrum. Furthermore, the wind input to waves is dominated by nonbreaking waves closer to the spectral peak. Shorter breaking waves, however, can support a significant fraction, which increases with wind speed, of the total air–sea momentum flux.
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Jin, Zunlong, Guoping Li, Junlei Wang, and Zhien Zhang. "Design, Modeling, and Experiments of the Vortex-Induced Vibration Piezoelectric Energy Harvester with Bionic Attachments." Complexity 2019 (April 4, 2019): 1–13. http://dx.doi.org/10.1155/2019/1670284.
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Since the energy demand increases, the sources of fluid energy such as wind energy and marine energy have attracted widespread attention, especially vortex-induced vibrations excited by wind energy. It is well known that the lock-in effect in vortex-induced vibration can be applied to the piezoelectric energy harvester. Although numerous researches have been conducted on piezoelectric energy harvesting devices in recent years, a common problem of low bandwidth and harvesting efficiency still exists. In order to increase the response amplitude and decrease the threshold wind speed of vortex-induced vibration, a bionic attachment structure is proposed based on the experimental method. In the present work, twelve models are designed according to the size of pits and hemispheric protrusions which are added to the surface of a flexible smooth cylinder. Compared with the smooth cylinder which is taken as a carrier, the harvester with the bionic structure shows stronger energy capture performance on the whole. As the threshold speed decelerates from 1.8m/s to 1 m/s, the bandwidth, on the contrary, increases from 39.3% to 51.4%. Particularly, for the 10 mm pits structure with 5 columns, its peak voltage can reach 47 V, and its peak power can reach 1.21 mW with a resistance of 800 kΩ, 0.57 mW higher than that of the smooth cylinder. Comparatively speaking, the hemispherical projections structure figures with a much more different energy capturing characteristic. Starting from the column, the measured voltage of the hemispherical bionic harvester is much smaller than that of the smooth cylinder, with a peak voltage less than 15 V and a reducing bandwidth. However, compared with the smooth cylinder, hemispheric projections with 3 columns have a better energy capture effect with a measured voltage of 35V, a resistance of 800kΩ, and a wind speed of 3.097 m/s. Besides, its output power also enhances from 0.48 to 0.56 mW.
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Reeves, Heather Dawn, and Richard Rotunno. "Orographic Flow Response to Variations in Upstream Humidity." Journal of the Atmospheric Sciences 65, no. 11 (November 1, 2008): 3557–70. http://dx.doi.org/10.1175/2008jas2762.1.
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Abstract The effects of upstream relative humidity (RH) on low-level wind and precipitation patterns for low-speed, statically stable flows over a mountain are investigated using idealized two- and three-dimensional numerical-simulation experiments in which RH is increased from 0% to 100%. For RH less than some critical threshold, the flow upstream becomes less decelerated as RH is increased; for RH greater than this threshold, the flow upstream becomes more decelerated as RH is increased. This increasing deceleration with RH is due to locally enhanced static stability resulting from enhanced condensation near the freezing level. Analyses from the simulations indicate that the lifted condensation level and the height of the freezing level are significant control parameters for the upstream-flow deceleration in the steady-state solutions. Dimensional analysis using these control parameters (as well as others) brings forth new nondimensional parameters that are shown to enter into analytic formulas for the orographic upstream-flow deceleration in a moist atmosphere.
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Palma, José M. L. M., Carlos A. M. Silva, Vítor C. Gomes, Alexandre Silva Lopes, Teresa Simões, Paula Costa, and Vasco T. P. Batista. "The digital terrain model in the computational modelling of the flow over the Perdigão site: the appropriate grid size." Wind Energy Science 5, no. 4 (November 5, 2020): 1469–85. http://dx.doi.org/10.5194/wes-5-1469-2020.
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Abstract. The digital terrain model (DTM), the representation of earth's surface at regularly spaced intervals, is the first input in the computational modelling of atmospheric flows. The ability of computational meshes based on high- (2 m; airborne laser scanning, ASL), medium- (10 m; military maps, Mil) and low-resolution (30 m; Shuttle Radar Topography Mission, SRTM) DTMs to replicate the Perdigão experiment site was appraised in two ways: by their ability to replicate the two main terrain attributes, elevation and slope, and by their effect on the wind flow computational results. The effect on the flow modelling was evaluated by comparing the wind speed, wind direction and turbulent kinetic energy using VENTOS®/2 at three locations, representative of the wind flow in the region. It was found that the SRTM was not an accurate representation of the Perdigão site. A 40 m mesh based on the highest-resolution data yielded an elevation error of less than 1.4 m and an RMSE of less than 2.5 m at five reference points compared to 5.0 m in the case of military maps and 7.6 m in the case of the SRTM. Mesh refinement beyond 40 m yielded no or insignificant changes on the flow field variables, wind speed, wind direction and turbulent kinetic energy. At least 40 m horizontal resolution – threshold resolution – based on topography available from aerial surveys is recommended in computational modelling of the flow over Perdigão.
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Pérez, Isidro A., M. Luisa Sánchez, M. Ángeles García, and Nuria Pardo. "Sensitivity of CO2 and CH4 Annual Cycles to Different Meteorological Variables at a Rural Site in Northern Spain." Advances in Meteorology 2019 (February 6, 2019): 1–11. http://dx.doi.org/10.1155/2019/9240568.
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The focus of the current paper is to explore the influence of meteorological variables on atmospheric CO2 and CH4 mean annual cycles at a rural site. Four variables were investigated: boundary layer height, recirculation factor, trajectory direction, and wind speed modelled at the altitude of the site. Boundary layer height and wind speed were provided by the METeorological data EXplorer (METEX) model. Recirculation factor and trajectory direction were obtained from calculations based on this trajectory model, and a nonparametric procedure was used to obtain a smooth evolution. The main results are higher concentrations obtained during the night, attributed to lower dispersion in this period. The smoothed values of the boundary layer height reached nearly 1200 m AGL during the day in August, and its low values caused high concentrations in spring. During the night, the recirculation factor and wind speed showed a sharp contrast between summer and winter. The average recirculation factor was low, 0.10, and average wind speed was 5.1 m·s−1. Trajectories were directionally distributed in four quadrants. Different tests were performed by selecting values of meteorological variables above or below certain thresholds. The influence of these variables reached values around 6.3 and 0.023 ppm for CO2 and CH4 average concentrations, respectively, during the day when the boundary layer was below 400 m. The main conclusion of this study is that the influence of meteorological variables should not be ignored. In particular, extremely low boundary layer heights may have noticeable effects on both gases.
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Berg, T., K. A. Pfaffhuber, A. S. Cole, O. Engelsen, and A. Steffen. "Ten-year trends in atmospheric mercury concentrations, meteorological effects and climate variables at Zeppelin, Ny-Ålesund." Atmospheric Chemistry and Physics 13, no. 13 (July 11, 2013): 6575–86. http://dx.doi.org/10.5194/acp-13-6575-2013.
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Abstract. Results from ten years of gaseous elemental mercury (GEM) measurements at Zeppelin station, Ny-Ålesund, Svalbard, show no overall annual trend between 2000 and 2009. Seasonal trend analysis showed significantly decreasing trends in January, February, March and June (−4.5 to −14.9 pg m−3 yr−1) and significantly increasing trends in May and July through December (1.5 to 28.7 pg m−3 yr −1). Results showed that atmospheric mercury depletion events (AMDEs) were equally distributed between April and May with only a few having been observed in March and June. A negative correlation between AMDEs and temperature is reported and supports earlier observations that AMDEs tend to occur at low temperatures. Lower concentrations of GEM were seen at lower temperatures below a threshold of 0 °C. The occurrence of AMDEs and wind direction were well correlated with the lowest GEM measured when the wind direction was from the Arctic Ocean region. Wind speed was found to not correlate with AMDEs, but the lowest GEM concentrations were observed at low wind speeds between 4 and 11 m s−1. AMDEs and relative humidity did not correlate well, but the lowest GEM levels appeared when the relative humidity was between 80 and 90%. Diurnal variation was observed especially during the month of March and is probably due to daytime snow surface emission induced by solar radiation. Relationships between GEM concentration and the Northern Hemisphere climate indices were investigated to assess if these climate parameters might reflect different atmospheric conditions that enhance or reduce spring AMDE activity. No consistent pattern was observed.
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van den Brink, H. W., G. P. Können, and J. D. Opsteegh. "Uncertainties in extreme surge level estimates from observational records." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 363, no. 1831 (June 15, 2005): 1377–86. http://dx.doi.org/10.1098/rsta.2005.1573.
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Ensemble simulations with a total length of 7540 years are generated with a climate model, and coupled to a simple surge model to transform the wind field over the North Sea to the skew surge level at Delfzijl, The Netherlands. The 65 constructed surge records, each with a record length of 116 years, are analysed with the generalized extreme value (GEV) and the generalized Pareto distribution (GPD) to study both the model and sample uncertainty in surge level estimates with a return period of 10 4 years, as derived from 116-year records. The optimal choice of the threshold, needed for an unbiased GPD estimate from peak over threshold (POT) values, cannot be determined objectively from a 100-year dataset. This fact, in combination with the sensitivity of the GPD estimate to the threshold, and its tendency towards too low estimates, leaves the application of the GEV distribution to storm-season maxima as the best approach. If the GPD analysis is applied, then the exceedance rate, λ , chosen should not be larger than 4. The climate model hints at the existence of a second population of very intense storms. As the existence of such a second population can never be excluded from a 100-year record, the estimated 10 4 -year wind-speed from such records has always to be interpreted as a lower limit.
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Masood, Nahid-Al, Md Nahid Haque Shazon, Hasin Mussayab Ahmed, and Shohana Rahman Deeba. "Mitigation of Over-Frequency through Optimal Allocation of BESS in a Low-Inertia Power System." Energies 13, no. 17 (September 2, 2020): 4555. http://dx.doi.org/10.3390/en13174555.
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The primary objective of this paper is to alleviate the over-frequency problem in low-inertia power systems through optimal allocation of a Battery Energy Storage System (BESS). With prolific integration of wind power, conventional fossil-fuel driven synchronous generators are being replaced in the generation fleet. Variable speed wind machines are connected to the grid via power electronics converters. As such, these machines usually do not participate in frequency regulation. During high wind penetration, a generation-rich zone of an interconnected power system may face significant over-frequency following the loss of interconnection. If the frequency goes above a certain threshold, an Over-Frequency Generator Shedding (OFGS) scheme is activated. This may cause considerable amount of generation cut in a low-inertia power system. To address this challenge, this paper develops a siting and sizing methodology of frequency-responsive BESS to simultaneously maintain frequency and voltage stabilities. As such, BESS is placed at the most voltage-sensitive bus, determined by an index called reactive power margin. Furthermore, an optimization model is formulated to determine the BESS size to avoid generation shedding. The proposed technique is applied to a low-inertia power system, which resembles the equivalent high-voltage transmission network of South Australia. The simulation results reveal that the developed methodology successfully mitigates the over-frequency phenomenon. In addition, the proposed technique is found to be more effective than its counterpart (i.e., without BESS) to enhance the frequency resilience of a low-inertia grid.
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Asheri, Emam Ali, and Nader Parvin. "Synoptic Pattern of Deep Trough Led to Strong Winds of Zab Basin in Iran." International Letters of Social and Humanistic Sciences 61 (October 2015): 46–52. http://dx.doi.org/10.18052/www.scipress.com/ilshs.61.46.
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One of the most important natural disasters are storms that each year, causing financial losses and Johnny are Frequency. Sometimes damage to the extent that the economic system, social disrupts a country. The aim of this study is to analyze the synoptic conditions of severe storms is Zab basin. In this study, given the scale of temporal and spatial distribution, wind speed and comprehensiveness of the three threshold size and calculate the 90th percentile wind speed, Forty days pervasive and severe storms were selected. Sea level pressure data and the elevation data of 500hp level from the database NCEP/NCAR were extracted. Matrix was formed that storm was on the rows and elevation data middle levels of the atmosphere, was on the columns. Then, principal components that explain the variation in height level pressure hp500 were identified. To identify synoptic patterns, cluster analysis integration "ward's" was performed on these components.The results showed that five synoptic pattern of atmospheric middle level, in the form of three major causes of severe storms in the Zab River Basin: Cut off low pattern, Shallow trough pattern of long wave and deep trough pattern of short wave. The most frequent traffic synoptic pattern of a synoptic pattern of middle levels and 60% of the patterns assigned to itself, causing severe storms in the Zab River Basin. Irregularities in the movement and position of the polar vortex caused the jet stream and storm paths meridian winds greater control and troughs are driven towards the low latitudes deeper. Because of the special arrangement of relatively strong and contrasting surface synoptic, the pressure gradient and energy exchange at its maximum reached compression Isobaric lines and as a result, Strong winds in the catchment area level has been created.
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Pavel, Amosov, Baklanov Alexander, Makarov Dmitriy, and Masloboev Vladimir. "Estimating air pollution levels by numerical simulation depending on wind flow speed and dust source area." Izvestiya vysshikh uchebnykh zavedenii Gornyi zhurnal, no. 5 (August 6, 2020): 80–89. http://dx.doi.org/10.21440/0536-1028-2020-5-80-89.
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Research aim is to estimate atmospheric pollution levels in the town of Apatity, by numerical simulation, depending on the discrete arrangement of dust sources at the tailing dump closest to the town and the speed of wind flow. Methodology. For computer 3D modeling, the COMSOL software was used. To calculate the aerodynamic properties the approach of incompressible fluid and standard (k–ε)-model of turbulence were used. The spread of dust pollution has been modeled by numerically solving the convective-diffusion equation of impurity transfer taking into account the deposition rate. Numerical experiments were performed for wind flow speeds between 5 and 23 m/s and a discrete representation of the dust source area between 2 and 10 ha. Results. The spatial distributions of the model's aerodynamic properties and the interval (and total) distributions of dust pollution were obtained. The Starye Apatity area is most exposed to atmospheric pollution. Atmospheric pollution levels were analyzed and generalized to functional dependencies, depending on the values of the model's variable parameters. It is shown that the calculated dependencies between the maximum dust concentration and the dust source area can be described by linear functions, which allows predicting the critical dust source area, at which the level of air pollution reaches the threshold limit value. It is demonstrated that the dependence of the maximum dust concentration on wind flow speed at fixed dust source area values can be approximated by a power-law function. Summary. A generalized analytical formula has been derived that allows predicting maximum dust concentrations in the town of Apatity depending on the discrete locations of dust sources at the tailing dump and the speed of wind flow.
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Hartl, Lea, Martin Stuefer, Tohru Saito, and Yoshitomi Okura. "History and Data Records of the Automatic Weather Station on Denali Pass (5715 m), 1990–2007." Journal of Applied Meteorology and Climatology 59, no. 12 (December 2020): 2113–27. http://dx.doi.org/10.1175/jamc-d-20-0082.1.
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AbstractWe present the data records and station history of an automatic weather station (AWS) on Denali Pass (5715 m MSL), Alaska. The station was installed by a team of climbers from the Japanese Alpine Club after a fatal accident involving Japanese climbers in 1989 and was operational intermittently between 1990 and 2007, measuring primarily air temperature and wind speed. In later years, the AWS was operated by the International Arctic Research Center of the University of Alaska Fairbanks. Station history is reconstructed from available documentation as archived by the expedition teams. To extract and preserve data records, the original datalogger files were processed. We highlight numerous challenges and sources of uncertainty resulting from the location of the station and the circumstances of its operation. The data records exemplify the harsh meteorological conditions at the site: air temperatures down to approximately −60°C were recorded, and wind speeds reached values in excess of 60 m s−1. Measured temperatures correlate strongly with reanalysis data at the 500-hPa level. An approximation of critical wind speed thresholds and a reanalysis-based reconstruction of the meteorological conditions during the 1989 accident confirm that the climbers faced extremely hazardous wind speeds and very low temperatures. The data from the Denali Pass AWS represent a unique historical record that can, we hope, serve as a basis for further monitoring efforts in the summit region of Denali.
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Barrett, Bradford S., Dominique Bastine Krieger, and Caroline P. Barlow. "Multiday Circulation and Precipitation Climatology during Winter Rain Events of Differing Intensities in Central Chile." Journal of Hydrometeorology 12, no. 5 (October 1, 2011): 1071–85. http://dx.doi.org/10.1175/2011jhm1377.1.
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Abstract The majority of precipitation in central Chile falls during austral winter with the passage of surface and upper-level low pressure systems and their associated surface fronts. Earlier studies have found the presence of a terrain-parallel, low-level barrier jet during cold front passage and low-level wind convergence in the region of heaviest precipitation. This study advances these findings by developing multiyear climatologies for a rainfall event in central Chile using a broad cross section of observational datasets: the Tropical Rainfall Measuring Mission (TRMM), the Atmospheric Infrared Sounder (AIRS), the National Climatic Data Center (NCDC) Global Surface Summary of the Day (GSOD), the Integrated Global Radiosonde Archive (IGRA), the Quick Scatterometer (QuikSCAT), and the NCEP–NCAR reanalysis. For this study, a precipitation event was defined as daily rainfall exceeding a certain threshold at a Santiago observing station (Pudahuel). Climatologies were developed for a five-day period surrounding the precipitation event: the three days leading up to the day of precipitation at Pudahuel, the day of the precipitation itself, and the day after. Precipitation was found to move northeastward over the southeast Pacific toward central Chile and increase in intensity upon reaching reached the coast between 33° and 40°S. At middle levels, a pronounced 500-hPa trough moved eastward and amplified during the same period, and at the surface, an area of low pressure deepened and followed the same path to the east. In the boundary layer and lower troposphere, winds at 925 and 850 hPa became exclusively north-northwesterly, suggesting the existence of a low-level jet, and surface winds backed with time and increased in speed ahead of a well-defined cold front wind shift. As these winds became more northwesterly ahead of the upper-level trough and surface low, precipitable water values increased, and a tongue of high precipitable water air intersected the coast at the same location as the region of heaviest precipitation. These climatologies, based on hundreds of cases, together provide strong confirmation that forcing associated with an eastward-progressing upper-level trough, a terrain-parallel low-level wind maximum, and an advancing surface cold front together constitute the complex, complementary mechanisms for precipitation in central Chile.
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Zentek, Rolf, Svenja H. E. Kohnemann, and Günther Heinemann. "Analysis of the performance of a ship-borne scanning wind lidar in the Arctic and Antarctic." Atmospheric Measurement Techniques 11, no. 10 (October 19, 2018): 5781–95. http://dx.doi.org/10.5194/amt-11-5781-2018.
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Abstract. In the present study a non-motion-stabilized scanning Doppler lidar was operated on board of RV Polarstern in the Arctic (June 2014) and Antarctic (December 2015–January 2016). This is the first time that such a system measured on an icebreaker in the Antarctic. A method for a motion correction of the data in the post-processing is presented. The wind calculation is based on vertical azimuth display (VAD) scans with eight directions that pass a quality control. Additionally a method for an empirical signal-to-noise ratio (SNR) threshold is presented, which can be calculated for individual measurement set-ups. Lidar wind profiles are compared to total of about 120 radiosonde profiles and also to wind measurements of the ship. The performance of the lidar measurements in comparison with radio soundings generally shows small root mean square deviation (bias) for wind speed of around 1 m s−1 (0.1 m s−1) and for wind direction of around 10∘ (1∘). The post-processing of the non-motion-stabilized data shows a comparably high quality to studies with motion-stabilized systems. Two case studies show that a flexible change in SNR threshold can be beneficial for special situations. Further the studies reveal that short-lived low-level jets in the atmospheric boundary layer can be captured by lidar measurements with a high temporal resolution in contrast to routine radio soundings. The present study shows that a non-motion-stabilized Doppler lidar can be operated successfully on an icebreaker. It presents a processing chain including quality control tests and error quantification, which is useful for further measurement campaigns.
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Hidayati, Rini, and Abytia Etika Banja. "Determination of Thermal Comforts Threshold on Students and Domestic Tourists in Lombok Island." Agromet 32, no. 2 (December 16, 2018): 71. http://dx.doi.org/10.29244/j.agromet.32.2.71-80.
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<p>The research aims to identify the comfort level on Lombok island, and to determine the comfort threshold values based on various thermal indices for indoor and outdoor. We applied three different indices namely Wet-Bulb Globe Temperature (WBGT), Temperature Humidity Index (THI), and Heat Stress Index (HSI). We observed climate variables including air temperature, relative humidity, wind speed, and black-globe temperature for periode February-March 2018. Then we correlated the indices against comfort and heat perceptions. Our results showed that altitude has influenced on the comfort index. Location on the higher altitude will have low index values, which were consistent for all indices. For the comfort threshold values, adaptation to local climate is the key to determine the values. The adapted people (students) will have a higher threshold value than those whom they were tourists. Our finding revealed that the threshold values for the indices were 28.5, 27.5, 92 for WBGT, THI, HSI, respectively. Based on our statistical analysis, we found that HSI was the best index to determine the comfort level in Lombok for the observed period, as the HSI has strong correlation with comfort and heat perceptions. Further, we recommend the wider used of HSI as the index uses more easily obtained climate variables.</p>
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Sidle, Roy C., and Alan D. Ziegler. "The canopy interception–landslide initiation conundrum: insight from a tropical secondary forest in northern Thailand." Hydrology and Earth System Sciences 21, no. 1 (January 31, 2017): 651–67. http://dx.doi.org/10.5194/hess-21-651-2017.
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Abstract. The interception and smoothing effect of forest canopies on pulses of incident rainfall and its delivery to the soil has been suggested as a factor in moderating peak pore water pressure in soil mantles, thus reducing the risk of shallow landslides. Here we provide 3 years of rainfall and throughfall data in a tropical secondary dipterocarp forest characterized by few large trees in northern Thailand, along with selected soil moisture dynamics, to address this issue. Throughfall was an estimated 88 % of rainfall, varying from 86 to 90 % in individual years. Data from 167 events demonstrate that canopy interception was only weakly associated (via a nonlinear relationship) with total event rainfall, but not significantly correlated with duration, mean intensity, or antecedent 2-day precipitation (API2). Mean interception during small events (≤ 35 mm) was 17 % (n = 135 events) compared with only 7 % for large events (> 35 mm; n = 32). Examining small temporal intervals within the largest and highest intensity events that would potentially trigger landslides revealed complex patterns of interception. The tropical forest canopy had little smoothing effect on incident rainfall during the largest events. During events with high peak intensities, high wind speeds, and/or moderate-to-high pre-event wetting, measured throughfall was occasionally higher than rainfall during large event peaks, demonstrating limited buffering. However, in events with little wetting and low-to-moderate wind speed, early event rainfall peaks were buffered by the canopy. As rainfall continued during most large events, there was little difference between rainfall and throughfall depths. A comparison of both rainfall and throughfall depths to conservative mean intensity–duration thresholds for landslide initiation revealed that throughfall exceeded the threshold in 75 % of the events in which rainfall exceeded the threshold for both wet and dry conditions. Throughfall intensity for the 11 largest events (rainfall = 65–116 mm) plotted near or above the intensity–duration threshold for landslide initiation during wet conditions; 5 of the events were near or above the threshold for dry conditions. Soil moisture responses during large events were heavily and progressively buffered at depths of 1 to 2 m, indicating that the timescale of any short-term smoothing of peak rainfall inputs (i.e., ≤ 1 h) has little influence on peak pore water pressure at depths where landslides would initiate in this area. Given these findings, we conclude that canopy interception would have little effect on mitigating shallow landslide initiation during the types of monsoon rainfall conditions in this and similar tropical secondary forest sites.