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1
Trotta, Domenico, Andrew P. Dimmock, Xochitl Blanco-Cano, Robert J. Forsyth, Heli Hietala, Naïs Fargette, Andrea Larosa, et al. "Observation of a Fully-formed Forward–Reverse Shock Pair due to the Interaction between Two Coronal Mass Ejections at 0.5 au." Astrophysical Journal Letters 971, no. 2 (August 1, 2024): L35. http://dx.doi.org/10.3847/2041-8213/ad68fa.
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Abstract We report direct observations of a fast magnetosonic forward–reverse shock pair observed by Solar Orbiter on 2022 March 8 at the short heliocentric distance of 0.5 au. The structure, sharing some features with fully-formed stream interaction regions, is due to the interaction between two successive coronal mass ejections (CMEs), never previously observed to give rise to a forward–reverse shock pair. The scenario is supported by remote observations from extreme ultraviolet cameras and coronagraphs, where two candidate eruptions compatible with the in situ signatures have been found. In the interaction region, we find enhanced energetic particle activity, strong nonradial flow deflections, and evidence of magnetic reconnection. At 1 au, well radially aligned Wind observations reveal a complex event, with characteristic observational signatures of both stream interaction region and CME–CME interaction, thus demonstrating the importance of investigating the complex dynamics governing solar eruptive phenomena.
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Wang, Mingming, and Leiming Zhang. "Synchronous Changes of GPP and Solar-Induced Chlorophyll Fluorescence in a Subtropical Evergreen Coniferous Forest." Plants 12, no. 11 (June 5, 2023): 2224. http://dx.doi.org/10.3390/plants12112224.
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Using in situ near-surface observations of solar-induced chlorophyll fluorescence (SIF) and gross primary productivity (GPP) of a subtropical evergreen coniferous forest in southern China, this study analyzed the dynamics of SIF, GPP and their environmental responses, and explored the potential of SIF in characterizing the variation of GPP. The results showed that SIF and GPP have similar diurnal and seasonal variation and both reach the highest value in summer, indicating that the SIF can be applied to indicate the seasonal variation of GPP for the subtropical evergreen co-niferous. With the increase in temporal scale, the correlation between SIF and GPP becomes more linear. The diurnal variations of both SIF and GPP were characterized by photosynthetically active radiation (PAR), the seasonal variations of SIF and GPP were influenced by air temperature (Ta) and PAR. Probably due to the absent of drought stress during the study period, no significant correlation was detected between soil water content (SWC) and either SIF or GPP. With the in-crease in Ta, PAR or SWC, the linear correlation between the SIF and GPP gradually decreased, and when Ta or PAR was relatively higher, the correlation between SIF and GPP become weakly. Further research is still needed to illustrate the relationship between SIF and GPP under drought condition which occurred frequently in this region based on longer observation.
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Gerland, S., G. E. Liston, J. G. winther, J. B. Ørbæk, and B. V. Ivanov. "Attenuation of solar radiation in Arctic snow: field observations and modelling." Annals of Glaciology 31 (2000): 364–68. http://dx.doi.org/10.3189/172756400781820444.
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AbstractSolar radiation was measured above and in the snowpack on Svalbard using a spectroradiometer and a quantum meter measuring average photosynthetically active radiation (PAR). In order to specify the effect of melting on the snow’s radiation properties, all measurements were performed before and during the melt season in May and June 1997 and 1998. Along with the radiation measurements, physical and structural snow properties were logged in snow pits. A physically based model was used to simulate the penetration of radiation into the snow The model formulation accounts for the spectrally dependent interactions between the radiation and snow grains, and requires inputs of the incoming solar radiation spectrum and the vertical snow density and grain-size. The vertical radiation-flux profile was computed using a two-stream radiation approximation where the absorption and reflection coefficients are related to the surface albedo, solar spectrum, grain-size and number of grains per unit volume. In general, snow before the onset of melt attenuates solar radiation more than coarser-grained snow that has been exposed to melting conditions. Quantum-meter measurements of PAR before and during melt can be explained by model outputs using both constant and variable extinction coefficients. Spectroradiometer measurements at fixed depth levels showed, in addition, that impurities in the snow reduce its transparency and therefore have the opposite effect to aging.
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Joiner, Joanna, Yasuko Yoshida, Philipp Köehler, Petya Campbell, Christian Frankenberg, Christiaan van der Tol, Peiqi Yang, Nicholas Parazoo, Luis Guanter, and Ying Sun. "Systematic Orbital Geometry-Dependent Variations in Satellite Solar-Induced Fluorescence (SIF) Retrievals." Remote Sensing 12, no. 15 (July 22, 2020): 2346. http://dx.doi.org/10.3390/rs12152346.
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While solar-induced fluorescence (SIF) shows promise as a remotely-sensed measurement directly related to photosynthesis, interpretation and validation of satellite-based SIF retrievals remains a challenge. SIF is influenced by the fraction of absorbed photosynthetically-active radiation at the canopy level that depends upon illumination geometry as well as the escape of SIF through the canopy that depends upon the viewing geometry. Several approaches to estimate the effects of sun-sensor geometry on satellite-based SIF have been proposed, and some have been implemented, most relying upon satellite reflectance measurements and/or other ancillary data sets. These approaches, designed to ultimately estimate intrinsic or physiological components of SIF related to photosynthesis, have not generally been applied globally to satellite measurements. Here, we examine in detail how SIF and related reflectance-based indices from wide swath polar orbiting satellites in low Earth orbit vary systematically due to the host satellite orbital characteristics. We compare SIF and reflectance-based parameters from the Global Ozone Mapping Experiment 2 (GOME-2) on the MetOp-B platform and from the TROPOspheric Monitoring Instrument (TROPOMI) on the Sentinel 5 Precursor satellite with a focus on high northern latitudes in summer where observations at similar geometries and local times occur. We show that GOME-2 and TROPOMI SIF observations agree nearly to within estimated uncertainties when they are compared at similar observing geometries. We show that the cross-track dependence of SIF normalized by PAR and related reflectance-based indices are highly correlated for dense canopies, but diverge substantially as the vegetation within a field-of-view becomes more sparse. This has implications for approaches that utilize reflectance measurements to help account for SIF geometrical dependences in satellite measurements. To further help interpret the GOME-2 and TROPOMI SIF observations, we simulated cross-track dependences of PAR normalized SIF and reflectance-based indices with the one dimensional Soil-Canopy Observation Photosynthesis and Energy fluxes (SCOPE) canopy radiative transfer model at sun–satellite geometries that occur across the wide swaths of these instruments and examine the geometrical dependencies of the various components (e.g., fraction of absorbed PAR, SIF yield, and escape of SIF from the canopy) of the observed SIF signal. The simulations show that most of the cross-track variations in SIF result from the escape of SIF through the scattering canopy and not the illumination.
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Bisoi, Susanta Kumar, and P. Janardhan. "Observations of a geomagnetic SI+ – SI− pair and associated solar wind fluctuations." Proceedings of the International Astronomical Union 8, S294 (August 2012): 543–44. http://dx.doi.org/10.1017/s1743921313003141.
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AbstractWe report a pair of oppositely directed sudden impulses (SI), in the geomagnetic field (ΔX), at ground stations, called SI+ – SI− pairs, that occurred between 1835 UT and 2300 UT on 23 April 1998. The SI+ – SI− pair, was well correlated with corresponding variations in the solar wind density, while solar wind velocity and the southward component of the interplanetary magnetic field (Bz) did not show any correspondence. This event had no source on the visible solar disk but was associated with a rear-side fast partial halo coronal mass ejection (CME) and an optically occulted M1.4 class solar flare behind the west limb. This event was unique in that one could clearly identify variations in ΔX at ground stations with solar wind parameters.
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Ren, Xiaoli, Honglin He, Li Zhang, and Guirui Yu. "Global radiation, photosynthetically active radiation, and the diffuse component dataset of China, 1981–2010." Earth System Science Data 10, no. 3 (July 5, 2018): 1217–26. http://dx.doi.org/10.5194/essd-10-1217-2018.
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Abstract. Solar radiation, especially photosynthetically active radiation (PAR), is the main energy source of plant photosynthesis, and the diffuse component can enhance canopy light use efficiency, thus increasing ecosystem productivity. In order to predict the terrestrial ecosystem productivity precisely, we not only need global radiation and PAR as driving variables, but also need to treat diffuse radiation and diffuse PAR explicitly in ecosystem models. Therefore, we generated a series of radiation datasets, including global radiation, diffuse radiation, PAR, and diffuse PAR of China from 1981 to 2010, based on the observations of the China Meteorology Administration (CMA) and the Chinese Ecosystem Research Network (CERN). The dataset should be useful for the analysis of the spatiotemporal variations of solar radiation in China and the impact of diffuse radiation on terrestrial ecosystem productivity based on ecosystem models. The dataset is freely available from Zenodo on the following website: https://zenodo.org/record/1198894#.Wx6–C_MwWo (https://doi.org/10.11922/sciencedb.555, Ren et al., 2018).
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Dorf, M., H. Bösch, A. Butz, C. Camy-Peyret, M. P. Chipperfield, A. Engel, F. Goutail, et al. "Balloon-borne stratospheric BrO measurements: comparison with Envisat/SCIAMACHY BrO limb profiles." Atmospheric Chemistry and Physics Discussions 5, no. 6 (December 19, 2005): 13011–52. http://dx.doi.org/10.5194/acpd-5-13011-2005.
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Abstract. For the first time, results of all four existing stratospheric BrO profiling instruments, are presented and compared with reference to the SLIMCAT 3-dimensional chemical transport model (3-D CTM). Model calculations are used to infer a BrO profile validation set, measured by 3 different balloon sensors, for the new Envisat/SCIAMACHY (ENVIronment SATellite/SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) satellite instrument. The balloon observations include (a) balloon-borne in situ resonance fluorescence detection of BrO, (b) balloon-borne solar occultation DOAS measurements (Differential Optical Absorption Spectroscopy) of BrO in the UV, and (c) BrO profiling from the solar occultation SAOZ (Systeme d'Analyse par Observation Zenithale) balloon instrument. Since stratospheric BrO is subject to considerable diurnal variation and none of the measurements are performed close enough in time and space for a direct comparison, all balloon observations are considered with reference to outputs from the 3-D CTM. The referencing is performed by forward and backward air mass trajectory calculations to match the balloon with the satellite observations. The diurnal variation of BrO is considered by 1-D photochemical model calculation along the trajectories. The 1-D photochemical model is initialised with output data of the 3-D model with additional constraints on the vertical transport, the total amount and photochemistry of stratospheric bromine as given by the various balloon observations. Total [Bry]=(20.1±2.8)pptv obtained from DOAS BrO observations at mid-latitudes in 2003, serves as an upper limit of the comparison. Most of the balloon observations agree with the photochemical model predictions within their given error estimates. First retrieval exercises of BrO limb profiling from the SCIAMACHY satellite instrument agree to <±50% with the photochemically-corrected balloon observations, and tend to show less agreement below 20 km.
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Bai, Jianhui. "Observations and estimations of PAR and solar visible radiation in North China." Journal of Atmospheric Chemistry 69, no. 3 (September 2012): 231–52. http://dx.doi.org/10.1007/s10874-012-9239-0.
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GUO, Haiqiang. "A dataset of carbon dioxide flux from Chongming Dongtan Wetland of Shanghai during 2004–2010." China Scientific Data 9, no. 1 (March 31, 2024): 1–5. http://dx.doi.org/10.11922/11-6035.csd.2023.0043.zh.
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As one of the standard methods of micrometeorology, eddy covariance technology has become the primary tool for monitoring the exchange of carbon dioxide, water and heat flux between terrestrial ecosystems and the atmosphere. This dataset includes the flux data accumulated by the National Observations and Research Station for Wetland Ecosystems in the Yangtze Estuary, collected in Dongtan Wetland on Chongming Island, Shanghai from September 2004 to December 2010, with a time resolution of half hour, and the data items cover air temperature (T_air), relative humidity (RH), soil temperature (T_soil), photosynthetically active radiation (PAR), solar radiation (Solar), net radiation (Rn), rainfall (Precip), sensible heat flux (Hs), latent heat flux (LE) and net carbon dioxide exchange (NEECO2), etc. The ecosystem observed in this study is typical of subtropical coastal salt marshes, predominantly inhabited by such plants as Phragmites australis and Spartina alterniflora. The observation system setup, equipment maintenance, data processing and quality control follows FLUXNET recommended protocols, ensuring high data reliability. The dataset can provide solid data support for the carbon budget, blue carbon estimation and biological invasion impact assessment of China's coastal salt marshes.
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Cubas Armas, Melania, and Damian Fabbian. "Do MURaM and STAGGER Simulations of Solar Faculae Match Observational Signatures from Magnetic Structures?" Astrophysical Journal 923, no. 2 (December 1, 2021): 207. http://dx.doi.org/10.3847/1538-4357/ac2605.
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Abstract We compare results of simulations of solar facular-like conditions performed using the numerical codes MURaM and STAGGER. Both simulation sets have a similar setup, including the initial condition of ≈200 G vertical magnetic flux. After interpolating the output physical quantities to constant optical depth, we compare them and test them against inversion results from solar observations. From the snapshots, we compute the monochromatic continuum in the visible and infrared, and the full Stokes vector of the Fe i spectral line pair around 6301–6302 Å. We compare the predicted spectral lines (at the simulation resolution and after smearing to the HINODE SP/SOT resolution) in terms of their main parameters for the Stokes I line profiles, and of their area and amplitude asymmetry for the Stokes V profiles. The codes produce magnetoconvection with similar appearance and distribution in temperature and velocity. The results also closely match the values from recent relevant solar observations. Although the overall distribution of the magnetic field is similar in both radiation-magnetohydrodynamic (RMHD) simulation sets, a detailed analysis reveals substantial disagreement in the field orientation, which we attribute to the differing boundary conditions. The resulting differences in the synthetic spectra disappear after spatial smearing to the resolution of the observations. We conclude that the two sets of simulations provide robust models of solar faculae. Nevertheless, we also find differences that call for caution when using results from RMHD simulations to interpret solar observational data.
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Gal-Yam, Avishay. "Pair-Instability Explosions: observational evidence." Proceedings of the International Astronomical Union 7, S279 (April 2011): 253–60. http://dx.doi.org/10.1017/s1743921312013014.
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AbstractIt has been theoretically predicted many decades ago that extremely massive stars that develop large oxygen cores will become dynamically unstable, due to electron-positron pair production. The collapse of such oxygen cores leads to powerful thermonuclear explosions that unbind the star and can produce, in some cases, many solar masses of radioactive 56Ni. For many years, no examples of this process were observed in nature. Here, I briefly review recent observations of luminous supernovae that likely result from pair-instability explosions, in the nearby and distant Universe.
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Kuznetsov, A. A., and E. P. Kontar. "First imaging spectroscopy observations of solar drift pair bursts." Astronomy & Astrophysics 631 (November 2019): L7. http://dx.doi.org/10.1051/0004-6361/201936447.
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Drift pairs are an unusual and puzzling type of fine structure sometimes observed in dynamic spectra of solar radio emission. They appear as two identical short narrowband drifting stripes separated in time; both positive and negative frequency drifts are observed. Currently, due to the lack of imaging observations, there is no satisfactory explanation for this phenomenon. Using the Low Frequency Array (LOFAR), we report unique observations of a cluster of drift pair bursts in the frequency range of 30−70 MHz made on 12 July 2017. Spectral imaging capabilities of the instrument have allowed us for the first time to resolve the temporal and frequency evolution of the source locations and sizes at a fixed frequency and along the drifting pair components. Sources of two components of a drift pair have been imaged and found to propagate in the same direction along nearly the same trajectories. Motion of the second component source is seen to be delayed in time with respect to that of the first one. The source trajectories can be complicated and non-radial; positive and negative frequency drifts correspond to opposite propagation directions. The drift pair bursts with positive and negative frequency drifts, as well as the associated broadband type-III-like bursts, are produced in the same regions. The visible source velocities are variable from zero to a few 104 (up to ∼105) km s−1, which often exceeds the velocities inferred from the drift rate (∼104 km s−1). The visible source sizes are of about 10′−18′; they are more compact than typical type III sources at the same frequencies. The existing models of drift pair bursts cannot adequately explain the observed features. We discuss the key issues that need to be addressed, and in particular the anisotropic scattering of the radio waves. The broadband bursts observed simultaneously with the drift pairs differ in some aspects from common type III bursts and may represent a separate type of emission.
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Dorf, M., H. Bösch, A. Butz, C. Camy-Peyret, M. P. Chipperfield, A. Engel, F. Goutail, et al. "Balloon-borne stratospheric BrO measurements: comparison with Envisat/SCIAMACHY BrO limb profiles." Atmospheric Chemistry and Physics 6, no. 9 (June 29, 2006): 2483–501. http://dx.doi.org/10.5194/acp-6-2483-2006.
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Abstract. For the first time, results of four stratospheric BrO profiling instruments, are presented and compared with reference to the SLIMCAT 3-dimensional chemical transport model (3-D CTM). Model calculations are used to infer a BrO profile validation set, measured by 3 different balloon sensors, for the new Envisat/SCIAMACHY (ENVIronment SATellite/SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) satellite instrument. The balloon observations include (a) balloon-borne in situ resonance fluorescence detection of BrO (Triple), (b) balloon-borne solar occultation DOAS measurements (Differential Optical Absorption Spectroscopy) of BrO in the UV, and (c) BrO profiling from the solar occultation SAOZ (Systeme d'Analyse par Observation Zenithale) balloon instrument. Since stratospheric BrO is subject to considerable diurnal variation and none of the measurements are performed close enough in time and space for a direct comparison, all balloon observations are considered with reference to outputs from the 3-D CTM. The referencing is performed by forward and backward air mass trajectory calculations to match the balloon with the satellite observations. The diurnal variation of BrO is considered by 1-D photochemical model calculation along the trajectories. The 1-D photochemical model is initialised with output data of the 3-D model with additional constraints on the vertical transport, the total amount and photochemistry of stratospheric bromine as given by the various balloon observations. Total [Bry]=(20.1±2.5) pptv obtained from DOAS BrO observations at mid-latitudes in 2003, serves as an upper limit of the comparison. Most of the balloon observations agree with the photochemical model predictions within their given error estimates. First retrieval exercises of BrO limb profiling from the SCIAMACHY satellite instrument on average agree to around 20% with the photochemically-corrected balloon observations of the remote sensing instruments (SAOZ and DOAS). An exception is the in situ Triple profile, in which the balloon and satellite data mostly does not agree within the given errors. In general, the satellite measurements show systematically higher values below 25 km than the balloon data and a change in profile shape above about 25 km.
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Hendrick, F., B. Barret, M. Van Roozendael, H. Boesch, A. Butz, M. De Mazière, F. Goutail, et al. "Retrieval of nitrogen dioxide stratospheric profiles from ground-based zenith-sky UV-visible observations: validation of the technique through correlative comparisons." Atmospheric Chemistry and Physics Discussions 4, no. 3 (May 25, 2004): 2867–904. http://dx.doi.org/10.5194/acpd-4-2867-2004.
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Abstract. A retrieval algorithm based on the Optimal Estimation Method (OEM) has been developed in order to provide vertical distributions of NO2 in the stratosphere from ground-based (GB) zenith-sky UV-visible observations. It has been applied to observational data sets from the NDSC (Network for Detection of Stratospheric Change) stations of Harestua (60° N, 10° E) and Andøya (69.3° N, 16.1° E) in Norway. The information content and retrieval errors have been analyzed following a formalism used for characterizing ozone profiles retrieved from solar infrared absorption spectra. In order to validate the technique, the retrieved NO2 vertical profiles and columns have been compared to correlative balloon and satellite observations. Such extensive validation of the profile and column retrievals was not reported in previously published work on the profiling from GB UV-visible measurements. A good agreement – generally better than 25% – has been found with the SAOZ (Système d'Analyse par Observations Zénithales) and DOAS (Differential Optical Absorption Spectroscopy) balloon data. A similar agreement has been reached with correlative satellite data from HALogen Occultation Experiment (HALOE) and Polar Ozone and Aerosol Measurement (POAM) III instruments above 25 km of altitude. Below 25 km, a systematic overestimation of our retrieved profiles – by up to 50% in some cases – has been observed by both HALOE and POAM III, pointing out the limitation of the satellite solar occultation technique at these altitudes. We have concluded that our study strengthens our confidence in the reliability of the retrieval of vertical distribution information from GB UV-visible observations and offers new perspectives in the use of GB UV-visible network data for validation purposes.
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Bai, Jianhui, Fengting Yang, Mingjie Xu, and Huimin Wang. "Empirical Models of Respiration and Net Ecosystem Productivity and Their Applications in a Subtropical Coniferous Plantation in China." Atmosphere 14, no. 10 (October 13, 2023): 1557. http://dx.doi.org/10.3390/atmos14101557.
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Net ecosystem exchange (NEE), solar radiation (including photosynthetically active radiation PAR), and meteorological parameters were measured in a subtropical coniferous plantation in China during 2013–2016. Applying the PAR balance principle at a canopy level and analyzing the observation data, an empirical model of respiration (Re, EMRe) considering 3-factor and 2-factor situations was developed and tested for all sky conditions. Generally, the respiration simulations were in reasonable agreement with the observations for the hourly, monthly, and annual sums of respiration. For example, using 3-factor and 2-factor models, the estimated annual sums of daytime and nighttime respiration in 2013–2016 overestimated that which was observed by about 31% and 26%, respectively. Further applications of EMRe and an empirical model of gross primary production (GPP, EMGPP) developed previously at this site, and an empirical model of net ecosystem productivity (NEP, EMNEP) using 3-factor and 2-factor models were obtained (NEP = GPP-Re) and evaluated for all sky conditions. Generally, the simulations of the hourly, monthly, and annual sums of NEP showed reasonable performances. The estimated NEP values overestimated the observations by 22% and 27% for the hourly sums in 2013–2016 when using the 3-factor and 2-factor models, respectively, and 7% and 12% for annual sums in 2013–2015 (2016 data were not used as the CO2 flux measurements had some problems in the 2016 summer). The NEP estimations were evidently improved when more factors (e.g., dark respiration) influencing Re were considered in the daytime respiration compared to those without considering these factors. To simplify the numerous and complicated CO2 processes in the simulations of Re and NEP, the PAR energy method was applied to capture and describe its main processes and energy interactions. The PAR energy method was suitable for studying the energy relationships associated with CO2 processes and developing empirical models for the simulations of GPP, Re, and NEP. These models were useful tools to investigate the multiple interactions and mechanisms between CO2, other atmospheric compositions, and PAR. Thus, the energy method is suggested to be applied to carbon balance.
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Bai, Jianhui, Fengting Yang, Huimin Wang, and Mingjie Xu. "An Empirical Model of Gross Primary Productivity (GPP) and Relations between GPP and Its Driving Factors, Biogenic Volatile Organic Compounds in a Subtropical Conifer Plantation in China." Atmosphere 14, no. 6 (June 17, 2023): 1046. http://dx.doi.org/10.3390/atmos14061046.
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Measurements of net ecosystem exchange (NEE), solar global radiation, photosynthetically active radiation (PAR) and meteorological parameters were carried out on a subtropical conifer plantation in China from 2013 to 2016. These observations were used to develop and evaluate an empirical model of gross primary production (GPP) (EMGPP) with 3-factor and 2-factor models. Using a 3-factor model, the simulated hourly GPP values were consistent with observations with a relative bias of 9.96% and normalized mean square error values of 0.07 mg CO2 m−2 s−1 for the scattering factor S/Q (S and Q are diffuse and global solar radiation) < 0.5 and 15.52% and 0.15 mg CO2 m−2 s−1 for S/Q ≥ 0.5. Validations of the EMGPP for hourly, daily, monthly, and annual GPP values were carried out and showed that both 3-factor and 2-factor EMGPP models can accurately capture diurnal, seasonal and interannual variations in GPP, but most simulated GPP overestimated the observed value. When the scattering factor is not available, the 2-factor EMGPP can be used. The EMGPP using 3-factor and 2-factor models was applied to simulate GPP under all sky conditions from 2013–2016, and the estimated GPP were in reasonable agreement with the measured values and showed systematic overestimations of 31% and 29% for mean hourly GPP and 41% and 29% for annual amounts, respectively. The sensitivity test demonstrated that GPP values were more sensitive to changes in PAR than to changes in water vapor and scattering factor at low S/Q, but were more sensitive to changes in water vapor than to PAR and S/Q at high S/Q. The sensitivity test revealed some mechanisms of GPP and its related processes, including the relationships between GPP and scattering of PAR, GPP and water vapor, which were in good agreement with other observations and model studies. An empirical model based on PAR energy balance can better describe the multiple interactions between GPP and its driving factors (PAR, water vapor, S/Q). The ratio of the emissions of biogenic volatile organic compounds (BVOCs) to net ecosystem exchange clearly varied between forests in different climate zones.
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Bai, Jianhui. "O3 Concentration and Its Relation with BVOC Emissions in a Subtropical Plantation." Atmosphere 12, no. 6 (May 31, 2021): 711. http://dx.doi.org/10.3390/atmos12060711.
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An empirical model of O3 is developed using the measurements of emissions of biogenic volatile organic compounds (BVOCs), O3 concentration, global solar radiation, photosynthetically active radiation (PAR) and meteorological variables in a subtropical Pinus plantation, China, during 2013–2016. In view of the different structures of isoprene and monoterpenes, two empirical models of O3 concentration are developed, considering PAR absorption and scattering due to gases, liquids and particles (GLPs), as well as PAR attenuation caused by O3 and BVOCs. The estimated O3 is in agreement with the observations, and validation of the O3 empirical model is conducted. O3 concentrations are more sensitive to changes in PAR and water vapor than S/Q (horizontal diffuse to global solar radiation) and BVOC emissions. O3 is positive to changes in isoprene emission at low light and high GLPs, or negative at high light and low GLPs; O3 is negative to changes in monoterpene emissions. O3 are positive with the changes of PAR, water vapor and S/Q. It is suggested to control human-induced high BVOC emissions, regulate plant cutting, and reduce NOx and SO2 emissions more strictly than ever before. There are inverted U-shape interactions between O3 and its driving factors, and S/Q controls their turning points.
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Cheng, Xiangfen, Yu Zhou, Meijun Hu, Feng Wang, Hui Huang, and Jinsong Zhang. "The Links between Canopy Solar-Induced Chlorophyll Fluorescence and Gross Primary Production Responses to Meteorological Factors in the Growing Season in Deciduous Broadleaf Forest." Remote Sensing 13, no. 12 (June 17, 2021): 2363. http://dx.doi.org/10.3390/rs13122363.
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Solar-induced chlorophyll fluorescence (SIF) is a hopeful indicator, which along with remote sensing, is used to measure the photosynthetic efficiency and gross primary production (GPP) of vegetation in regional terrestrial ecosystems. Studies have found a significant linear correlation between SIF and GPP in a variety of ecosystems. However, this relationship has mainly been established using SIF and GPP data derived from satellite remote sensing and continuous ground-based observations, respectively, which are difficult to accurately match. To overcome this, some studies have begun to use tower-based automatic observation instruments to study the changes of near-surface SIF and GPP. This study conducts continuous simultaneous observation of SIF, carbon flux, and meteorological factors on the forest canopy of a cork oak plantation during the growing season to explore how meteorological factors impact on canopy SIF and its relationship with GPP. This research found that the canopy SIF has obvious diurnal and day-to-day variations during the growing season but overall is relatively stable. Furthermore, SIF is greatly affected by incident radiation in different weather conditions and can change daily. Meteorological factors have a major role in the relationship between SIF and GPP; overall, the relationship shows a significant linear regression on the 30 min scale, but weakens when aggregating to the diurnal scale. Photosynthetically active radiation (PAR) drives SIF on a daily basis and changes the relationship between SIF and GPP on a seasonal timescale. As PAR increases, the daily slopes of the linear regressions between SIF and GPP decrease. On the 30 min timescale, both SIF and GPP increase with PAR until it reaches 1250 μmol·m−2·s−1; subsequently, SIF continues to increase while GPP decreases and they show opposite trends. Soil moisture and vapor pressure deficit influence SIF and GPP, respectively. Our findings demonstrate that meteorological factors affect the relationship between SIF and GPP, thereby enhancing the understanding of the mechanistic link between chlorophyll fluorescence and photosynthesis.
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Chang, Che-Jui, and Jean-Fu Kiang. "Simulations of Switchback, Fragmentation and Sunspot Pair in δ-Sunspots during Magnetic Flux Emergence." Sensors 21, no. 2 (January 15, 2021): 586. http://dx.doi.org/10.3390/s21020586.
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Strong flares and coronal mass ejections (CMEs), launched from δ-sunspots, are the most catastrophic energy-releasing events in the solar system. The formations of δ-sunspots and relevant polarity inversion lines (PILs) are crucial for the understanding of flare eruptions and CMEs. In this work, the kink-stable, spot-spot-type δ-sunspots induced by flux emergence are simulated, under different subphotospheric initial conditions of magnetic field strength, radius, twist, and depth. The time evolution of various plasma variables of the δ-sunspots are simulated and compared with the observation data, including magnetic bipolar structures, relevant PILs, and temperature. The simulation results show that magnetic polarities display switchbacks at a certain stage and then split into numerous fragments. The simulated fragmentation phenomenon in some δ-sunspots may provide leads for future observations in the field.
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Holtby, L. Blair, and Max L. Bothwell. "Effects of solar ultraviolet radiation on the behaviour of juvenile coho salmon (Oncorhynchus kisutch): avoidance, feeding, and agonistic interactions." Canadian Journal of Fisheries and Aquatic Sciences 65, no. 4 (April 1, 2008): 701–11. http://dx.doi.org/10.1139/f08-013.
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The behaviour of juvenile coho salmon (Oncorhynchus kisutch) was observed in outdoor experimental flumes in which three different spectral regimes were created by plastic covers that selectively blocked all or portions of natural ultraviolet radiation (UVR). The three light treatments were (i) photosynthetically active radiation (PAR, 400–700 nm), (ii) PAR plus longer wavelength ultraviolet (PAR + UVA, 320–700 nm), and (iii) full-spectrum sunlight with both long and short wavelength ultraviolet included (PAR + UVA + UVB, 280–700 nm). Observations made at different times of the day and under both overcast and sunny skies allowed an assessment of PAR intensity on behaviour in addition to that of UVR. We quantified shade-seeking behaviour, feeding strikes, and agonistic interactions (approaches, chases, and nips) between individuals. Under higher PAR intensities, a greater proportion of juvenile coho tended to take cover under rocks. Shade-seeking behaviour increased significantly in the presence of UVR. Feeding and agonistic interactions were partially inhibited at higher PAR intensities and very significantly depressed by UVR. For all behaviours tested, the effects were mediated by UVA with no significant additional impacts from UVB. UVR-mediated effects on behaviour could have ecological consequences through influencing summer densities, density-dependent growth, and size-dependent winter and early marine survivals.
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Verkhoglyadova, O. P., B. Dasgupta, and B. T. Tsurutani. "Model for vortex turbulence with discontinuities in the solar wind." Nonlinear Processes in Geophysics 10, no. 4/5 (October 31, 2003): 335–43. http://dx.doi.org/10.5194/npg-10-335-2003.
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Abstract. A model of vortex with embedded discontinuities in plasma flow is developed in the framework of ideal MHD in a low b plasma. Vortex structures are considered as a result of 2-D evolution of nonlinear shear Alfvén waves in the heliosphere. Physical properties of the solutions and vector fields are analyzed and the observational aspects of the model are discussed. The ratio of normal components to the discontinuity Br /Vr can be close to -2. The alignment between velocity and magnetic field vectors takes place. Spacecraft crossing such vortices will typically observe a pair of discontinuities, but with dissimilar properties. Occurrence rate for different discontinuity types is estimated and agrees with observations in high-speed solar wind stream. Discontinuity crossing provides a backward rotation of magnetic field vector and can be observed as part of a backward arc. The Ulysses magnetometer data obtained in the fast solar wind are compared with the results of theoretical modelling.
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Volvach, Ya, A. Stanislavsky, A. Konovalenko, A. Koval, and V. Dorovskyy. "Comparative analysis of decametre 'drift pair' bursts observed in 2002 and 2015." Advances in Astronomy and Space Physics 6, no. 1 (2016): 24–27. http://dx.doi.org/10.17721/2227-1481.6.24-27.
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We report about new observations of solar 'drift pair' (DP) bursts by means of the UTR-2 radio telescope at frequencies 10-30 MHz. Our experimental data include both 'forward' and 'reverse' bursts with high frequency and time resolution. The records of 301 bursts, observed in 10-12 July of 2015, are investigated. The main properties of these bursts (frequency bandwidth, central frequency and others) have been analysed. In this report our main attention is paid to the comparison of our observations with the similar observations of decametre DPs performed earlier during 13-15 July of 2002 in the same frequency range. Common features of DPs in the two different pieces of data samples have been found. This may indicate the possible presence of stability in the frequency-time properties of decametre DPs from one cycle of solar activity to another.
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Melnik, Valentin N., Alexander A. Konovalenko, Helmut O. Rucker, and Alain Lecacheux. "Sporadic radio emission of the Sun in the decametre range." Proceedings of the International Astronomical Union 2, no. 14 (August 2006): 365–66. http://dx.doi.org/10.1017/s1743921307011003.
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AbstractResults of the last observations of solar sporadic radio emission at the UTR-2 radio telescope (Kharkov, Ukraine) at the frequencies 10 - 30 MHz are presented. The use of new backend facilities, the DSP and 60-channel spectrometer, allows us to obtain data with time resolution up to 2 ms and frequency resolution of 12 kHz in the continuous frequency band 12 MHz. Usual Type III bursts, Type IIIb bursts, U- and J-bursts in the decameter range are discussed. Special attention is paid to detection and analysis of Type II bursts and their properties, newly discovered fine time structures of Type III bursts, Type III-like bursts, s-bursts, new observational features of drift pair bursts, and ‘absorption’ bursts.
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Heidrich-Meisner, Verena, Lars Berger, and Robert F. Wimmer-Schweingruber. "Proton-proton collisional age to order solar wind types." Astronomy & Astrophysics 636 (April 2020): A103. http://dx.doi.org/10.1051/0004-6361/201937378.
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Context. The properties of a solar wind stream are determined by its source region and by transport effects. Independently of the solar wind type, the solar wind measured in situ is always affected by both. This means that reliably determining the solar wind type from in situ observations is useful for the analysis of its solar origin and its evolution during the travel time to the spacecraft that observes the solar wind. In addition, the solar wind type also influences the interaction of the solar wind with other plasma such as Earth’s magnetosphere. Aims. We consider the proton-proton collisional age as an ordering parameter for the solar wind at 1 AU and explore its relation to the solar wind classification scheme developed by Xu & Borovsky (2015, J. Geophys. Res.: Space Phys., 120, 70). We use this to show that explicit magnetic field information is not required for this solar wind classification. Furthermore, we illustrate that solar wind classification schemes that rely on threshold values of solar wind parameters should depend on the phase in the solar activity cycle since the respective parameters change with the solar activity cycle. Methods. The categorization of the solar wind following Xu & Borovsky (2015, J. Geophys. Res.: Space Phys., 120, 70) was taken as our reference for determining the solar wind type. Based on the observation that the three basic solar wind types from this categorization cover different regimes in terms of proton-proton collisional age acol, p-p, we propose a simplified solar wind classification scheme that is only based on the proton-proton collisional age. We call the resulting method the PAC solar wind classifier. For this purpose, we derive time-dependent threshold values in the proton-proton collisional age for two variants of the proposed PAC scheme: (1) similarity-PAC is based on the similarity to the full Xu & Borovsky (2015, J. Geophys. Res.: Space Phys., 120, 70) scheme, and (2) distribution-PAC is based directly on the distribution of the proton-proton collisional age. Results. The proposed simplified solar wind categorization scheme based on the proton-proton collisional age represents an equivalent alternative to the full Xu & Borovsky (2015, J. Geophys. Res.: Space Phys., 120, 70) solar wind classification scheme and leads to a classification that is very similar to the full Xu & Borovsky (2015, J. Geophys. Res.: Space Phys., 120, 70) scheme. The proposed PAC solar wind categorization separates coronal hole wind from helmet-streamer plasma as well as helmet-streamer plasma (slow solar wind without a current sheet crossing) from sector-reversal plasma (slow solar wind with a current sheet crossing). Unlike the full Xu & Borovsky (2015, J. Geophys. Res.: Space Phys., 120, 70) scheme, PAC does not require information on the magnetic field as input. Conclusions. The solar wind is well ordered by the proton-proton collisional age. This implies underlying intrinsic relationships between the plasma properties, in particular, proton temperature and magnetic field strength in each plasma regime. We argue that sector-reversal plasma is a combination of particularly slow and dense solar wind and most stream interaction boundaries. Most solar wind parameters (e.g., the magnetic field strength, B, and the oxygen charge state ratio no7+/no6+) change with the solar activity cycle. Thus, all solar wind categorization schemes based on threshold values need to be adapted to the solar activity cycle as well. Because it does not require magnetic field information but only proton plasma measurements, the proposed PAC solar wind classifier can be applied directly to solar wind data from the Solar and Heliospheric Observatoty (SOHO), which is not equipped with a magnetometer.
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Rastogi, R. G., P. Janardhan, K. Ahmed, A. C. Das, and Susanta K. Bisoi. "Unique observations of a geomagnetic SI+− SI−pair: Solar sources and associated solar wind fluctuations." Journal of Geophysical Research: Space Physics 115, A12 (December 2010): n/a. http://dx.doi.org/10.1029/2010ja015708.
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Shen, Yuandeng, Dongxu Liu, Surui Yao, Chengrui Zhou, Zehao Tang, Zhining Qu, Xinping Zhou, Yadan Duan, Song Tan, and Ahmed Ahmed Ibrahim. "Double-decker Pair of Flux Ropes Formed by Two Successive Tether-cutting Eruptions." Astrophysical Journal 964, no. 2 (March 22, 2024): 125. http://dx.doi.org/10.3847/1538-4357/ad2349.
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Abstract Double-decker filaments and their eruptions have been widely observed in recent years, but their physical formation mechanism is still unclear. Using high spatiotemporal resolution, multi-wavelength observations taken by the New Vacuum Solar Telescope and the Solar Dynamics Observatory, we show the formation of a double-decker pair of flux rope system by two successive tether-cutting eruptions in a bipolar active region. Due to the combined effect of photospheric shearing and convergence motions around the active region’s polarity inversion line (PIL), the arms of two overlapping inverse-S-shaped short filaments reconnected at their intersection, which created a simultaneous upward-moving magnetic flux rope (MFR) and a downward-moving post-flare-loop (PFL) system striding the PIL. Meanwhile, four bright flare ribbons appeared at the footpoints of the newly formed MFR and the PFL. As the MFR rose, two elongated flare ribbons connected by a relatively larger PFL appeared on either side of the PIL. After a few minutes, another MFR formed in the same way at the same location and then erupted in the same direction as the first one. Detailed observational results suggest that the eruption of the first MFR might experienced a short pause before its successful eruption, while the second MFR was a failed eruption. This implies that the two newly formed MFRs might reach a new equilibrium at relatively higher heights for a while, which can be regarded as a transient double-decker flux rope system. The observations can well be explained by the tether-cutting model, and we propose that two successive confined tether-cutting eruptions can naturally produce a double-decker flux rope system, especially when the background coronal magnetic field has a saddle-like distribution of magnetic decay index profile in height.
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Hendrick, F., B. Barret, M. Van Roozendael, H. Boesch, A. Butz, M. De Mazière, F. Goutail, et al. "Retrieval of nitrogen dioxide stratospheric profiles from ground-based zenith-sky UV-visible observations: validation of the technique through correlative comparisons." Atmospheric Chemistry and Physics 4, no. 8 (October 21, 2004): 2091–106. http://dx.doi.org/10.5194/acp-4-2091-2004.
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Abstract. A retrieval algorithm based on the Optimal Estimation Method (OEM) has been developed in order to provide vertical distributions of NO2 in the stratosphere from ground-based (GB) zenith-sky UV-visible observations. It has been applied to observational data sets from the NDSC (Network for Detection of Stratospheric Change) stations of Harestua (60° N, 10° E) and Andøya (69° N, 16° E) in Norway. The information content and retrieval errors have been analyzed following a formalism used for characterizing ozone profiles retrieved from solar infrared absorption spectra. In order to validate the technique, the retrieved NO2 vertical profiles and columns have been compared to correlative balloon and satellite observations. Such extensive validation of the profile and column retrievals was not reported in previously published work on the profiling from GB UV-visible measurements. A good agreement - generally better than 25% - has been found with the SAOZ (Système d'Analyse par Observations Zénithales) and DOAS (Differential Optical Absorption Spectroscopy) balloons. A similar agreement has been reached with correlative satellite data from the HALogen Occultation Experiment (HALOE) and Polar Ozone and Aerosol Measurement (POAM) III instruments above 25km of altitude. Below 25km, a systematic underestimation - by up to 40% in some cases - of both HALOE and POAM III profiles by our GB profile retrievals has been observed, pointing out more likely a limitation of both satellite instruments at these altitudes. We have concluded that our study strengthens our confidence in the reliability of the retrieval of vertical distribution information from GB UV-visible observations and offers new perspectives in the use of GB UV-visible network data for validation purposes.
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Shume, E. B., A. J. Mannucci, and R. Caton. "Phase and coherence analysis of VHF scintillation over Christmas Island." Annales Geophysicae 32, no. 3 (March 28, 2014): 293–300. http://dx.doi.org/10.5194/angeo-32-293-2014.
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Abstract. This short paper presents phase and coherence data from the cross-wavelet transform applied on longitudinally separated very high frequency (VHF) equatorial ionospheric scintillation observations over Christmas Island. The phase and coherence analyses were employed on a pair of scintillation observations, namely, the east-looking and west-looking VHF scintillation monitors at Christmas Island. Our analysis includes 3 years of peak season scintillation data from 2008, 2009 (low solar activity), and 2011 (moderate solar activity). In statistically significant and high spectral coherence regions of the cross-wavelet transform, scintillation observations from the east-looking monitor lead those from the west-looking monitor by about 20 to 60 (40 ± 20) min (most frequent lead times). Using several years (seasons and solar cycle) of lead (or lag) and coherence information of the cross-wavelet transform, we envisage construction of a probability model for forecasting scintillation in the nighttime equatorial ionosphere.
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Fritzewski, D. J., S. A. Barnes, D. J. James, A. M. Geller, S. Meibom, and K. G. Strassmeier. "Spectroscopic membership for the populous 300 Myr-old open cluster NGC 3532." Astronomy & Astrophysics 622 (February 2019): A110. http://dx.doi.org/10.1051/0004-6361/201833587.
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Context. NGC 3532 is an extremely rich open cluster embedded in the Galactic disc, hitherto lacking a comprehensive, documented membership list. Aims. We provide membership probabilities from new radial velocity observations of solar-type and low-mass stars in NGC 3532, in part as a prelude to a subsequent study of stellar rotation in the cluster. Methods. Using extant optical and infra-red photometry we constructed a preliminary photometric membership catalogue, consisting of 2230 dwarf and turn-off stars. We selected 1060 of these for observation with the AAOmega spectrograph at the 3.9 m-Anglo-Australian Telescope and 391 stars for observations with the Hydra-South spectrograph at the 4 m Victor Blanco Telescope, obtaining spectroscopic observations over a decade for 145 stars. We measured radial velocities for our targets through cross-correlation with model spectra and standard stars, and supplemented them with radial velocities for 433 additional stars from the literature. We also measured log g, Teff, and [Fe/H] from the AAOmega spectra. Results. The radial velocity distribution emerging from the observations is centred at 5.43 ± 0.04 km s−1 and has a width (standard deviation) of 1.46 km s−1. Together with proper motions from Gaia DR2 we find 660 exclusive members, of which five are likely binary members. The members are distributed across the whole cluster sequence, from giant stars to M dwarfs, making NGC 3532 one of the richest Galactic open clusters known to date, on par with the Pleiades. From further spectroscopic analysis of 153 dwarf members we find the metallicity to be marginally sub-solar, with [Fe/H] = −0.07 ± 0.10. We confirm the extremely low reddening of the cluster, EB − V = 0.034 ± 0.012 mag, despite its location near the Galactic plane. Exploiting trigonometric parallax measurements from Gaia DR2 we find a distance of 48435−30 pc [(m − M)0 = 8.42 ± 0.14 mag]. Based on the membership we provide an empirical cluster sequence in multiple photometric passbands. A comparison of the photometry of the measured cluster members with several recent model isochrones enables us to confirm the 300 Myr cluster age. However, all of the models evince departures from the cluster sequence in particular regions, especially in the lower mass range.
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Hu, Meijun, Xiangfen Cheng, Jinsong Zhang, Hui Huang, Yu Zhou, Xin Wang, Qingmei Pan, and Chongfan Guan. "Temporal Variation in Tower-Based Solar-Induced Chlorophyll Fluorescence and Its Environmental Response in a Chinese Cork Oak Plantation." Remote Sensing 15, no. 14 (July 16, 2023): 3568. http://dx.doi.org/10.3390/rs15143568.
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With the development of spectrum observation technology, solar-induced chlorophyll fluorescence (SIF)—an effective substitute for photosynthesis—has been widely used to monitor crop stress, vegetation phenology and ecosystem productivity. The relationship between fluorescence and photosynthesis is complicated because they are sensitive to environmental changes. Understanding the response of SIF to environmental factors is of great significance for clarifying the variation dynamic and relationship between SIF and photosynthesis under different conditions. In this study, the canopy SIF and the environmental factors of a Quercus variabilis BI. plantation were observed simultaneously, and the response of SIF to environmental factors at a daily scale and at a half-hour scale was analyzed. The results showed that SIF had obvious seasonal and diurnal dynamics and was mainly driven by photosynthetically active radiation (PAR). The influence of PAR, air temperature (Ta), vapor pressure deficit (VPD), soil moisture (SM) and wind speed (Ws) on SIF varied with the lapse of the growing season. After eliminating the covariant effect of PAR on the Ta and VPD during the whole growing season, the relationship between VPD and SIF was found to be negative, and the effect of Ta on SIF disappeared. This study enriched the ground observation dataset and provided support for understanding the variations in the relationship between SIF and photosynthesis under different conditions.
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Petrova, Evgeniya V., and Victor I. Grokhovsky. "High pressure impacts on meteorites." Pure and Applied Chemistry 91, no. 11 (November 26, 2019): 1857–67. http://dx.doi.org/10.1515/pac-2018-1119.
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Abstract In the invited article, we review observations on changes in meteorite texture relevant to the early stages of formation of the Solar System based on the experimental shock wave loading of the material at the laboratory. Investigation of the physical and structural properties of high-pressure impacts on meteorites is important for few reasons, such as: Protection of the Earth from the near-Earth objects (NEOs); Study of processes that cannot yet be achieved under laboratory conditions; Understanding of conditions for asteroid mining.
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Feng, Lan, Wenmin Qin, Lunche Wang, Aiwen Lin, and Ming Zhang. "Comparison of Artificial Intelligence and Physical Models for Forecasting Photosynthetically-Active Radiation." Remote Sensing 10, no. 11 (November 21, 2018): 1855. http://dx.doi.org/10.3390/rs10111855.
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Different kinds of radiative transfer models, including a relative sunshine-based model (BBM), a physical-based model for tropical environment (PBM), an efficient physical-based model (EPP), a look-up-table-based model (LUT), and six artificial intelligence models (AI) were introduced for modeling the daily photosynthetically-active radiation (PAR, solar radiation at 400–700 nm), using ground observations at twenty-nine stations, in different climatic zones and terrain features, over mainland China. The climate and terrain effects on the PAR estimates from the different PAR models have been quantitatively analyzed. The results showed that the Genetic model had overwhelmingly higher accuracy than the other models, with the lowest root mean square error (RMSE = 0.5 MJ m−2day−1), lowest mean absolute bias error (MAE = 0.326 MJ m−2day−1), and highest correlation coefficient (R = 0.972), respectively. The spatial–temporal variations of the annual mean PAR (APAR), in the different climate zones and terrains over mainland China, were further investigated, using the Genetic model; the PAR values in China were generally higher in summer than those in the other seasons. The Qinghai Tibetan Plateau had always been the area with the highest APAR (8.668 MJ m−2day−1), and the Sichuan Basin had always been the area with lowest APAR (4.733 MJ m−2day−1). The PAR datasets generated by the Genetic model, in this study, could be used in numerous PAR applications, with high accuracy.
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Balabin, Yury V., Alexey V. Germanenko, Evgeniy A. Maurchev, Evgeniya A. Mikhalko, and Boris B. Gvozdevsky. "Muon telescopes of the polar stations Apatity and Barentsburg for observations of small variations of cosmic rays." Transactions of the Kоla Science Centre. Series: Natural Sciences and Humanities 2, no. 2/2023 (July 3, 2023): 5–12. http://dx.doi.org/10.37614/2949-1185.2023.2.2.001.
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The first results of the operation of a pair of muon telescopes installed at the Apatity and Barentsburg stations (Svalbard) in addition to the existing neutron monitors are presented. A technique for separating small variations against the background of stronger variations caused by solar activity is proposed. With its help, a small anisotropy of cosmic rays between the directions of reception of muon telescopes was revealed. It is still difficult to judge the reasons for such anisotropy, since the period of solar activity is 11 years, and observations were made for just over a year
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Pagán, Brianna, Wouter Maes, Pierre Gentine, Brecht Martens, and Diego Miralles. "Exploring the Potential of Satellite Solar-Induced Fluorescence to Constrain Global Transpiration Estimates." Remote Sensing 11, no. 4 (February 18, 2019): 413. http://dx.doi.org/10.3390/rs11040413.
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The opening and closing of plant stomata regulates the global water, carbon and energy cycles. Biophysical feedbacks on climate are highly dependent on transpiration, which is mediated by vegetation phenology and plant responses to stress conditions. Here, we explore the potential of satellite observations of solar-induced chlorophyll fluorescence (SIF)—normalized by photosynthetically-active radiation (PAR)—to diagnose the ratio of transpiration to potential evaporation (‘transpiration efficiency’, τ). This potential is validated at 25 eddy-covariance sites from seven biomes worldwide. The skill of the state-of-the-art land surface models (LSMs) from the eartH2Observe project to estimate τ is also contrasted against eddy-covariance data. Despite its relatively coarse (0.5°) resolution, SIF/PAR estimates, based on data from the Global Ozone Monitoring Experiment 2 (GOME-2) and the Clouds and Earth’s Radiant Energy System (CERES), correlate to the in situ τ significantly (average inter-site correlation of 0.59), with higher correlations during growing seasons (0.64) compared to decaying periods (0.53). In addition, the skill to diagnose the variability of in situ τ demonstrated by all LSMs is on average lower, indicating the potential of SIF data to constrain the formulations of transpiration in global models via, e.g., data assimilation. Overall, SIF/PAR estimates successfully capture the effect of phenological changes and environmental stress on natural ecosystem transpiration, adequately reflecting the timing of this variability without complex parameterizations.
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Si, Xiaolong, Xiuju Li, Hongyao Chen, Shiwei Bao, Heyu Xu, Liming Zhang, and Wenxin Huang. "Research on a Partial Aperture Factor Measurement Method for the AGRI Onboard Calibration Assembly." Sensors 22, no. 5 (February 25, 2022): 1832. http://dx.doi.org/10.3390/s22051832.
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A partial aperture onboard calibration method can solve the onboard calibration problems of some large aperture remote sensors, which is of great significance for the development trend of increasingly large apertures in optical remote sensors. In this paper, the solar diffuser reflectance degradation monitor (SDRDM) in the onboard calibration assembly (CA) of the FengYun-4 (FY-4) advanced geostationary radiance imager (AGRI) was used as the reference radiometer. It was designed for measuring the partial aperture factor (PAF) for the AGRI onboard calibration. First, the linear response count variation relationship between the two was established under the same radiance source input. Then, according to the known bidirectional reflection distribution function (BRDF) of the solar diffuser (SD) in the CA, the relative reflectance ratio coefficient between the AGRI observation direction and the SDRDM observation direction was calculated. On this basis, the response count value of the AGRI and the SDRDM was used to realize the high-precision measurement of the PAF of the AGRI B1~B3 bands by simulating the AGRI onboard calibration measurement under the illumination of a solar simulator in the laboratory. According to the determination process of the relevant parameters of the PAF, the measurement uncertainty of the PAF was analyzed; this uncertainty was greater than 2.04% and provided an important reference for the evaluation of the onboard absolute radiometric calibration uncertainty after launch.
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Du, Shanshan, Liangyun Liu, Xinjie Liu, Jian Guo, Jiaochan Hu, Shaoqiang Wang, and Yongguang Zhang. "SIFSpec: Measuring Solar-Induced Chlorophyll Fluorescence Observations for Remote Sensing of Photosynthesis." Sensors 19, no. 13 (July 8, 2019): 3009. http://dx.doi.org/10.3390/s19133009.
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Solar-induced chlorophyll fluorescence (SIF) is regarded as a proxy for photosynthesis in terrestrial vegetation. Tower-based long-term observations of SIF are very important for gaining further insight into the ecosystem-specific seasonal dynamics of photosynthetic activity, including gross primary production (GPP). Here, we present the design and operation of the tower-based automated SIF measurement (SIFSpec) system. This system was developed with the aim of obtaining synchronous SIF observations and flux measurements across different terrestrial ecosystems, as well as to validate the increasing number of satellite SIF products using in situ measurements. Details of the system components, instrument installation, calibration, data collection, and processing are introduced. Atmospheric correction is also included in the data processing chain, which is important, but usually ignored for tower-based SIF measurements. Continuous measurements made across two growing cycles over maize at a Daman (DM) flux site (in Gansu province, China) demonstrate the reliable performance of SIF as an indicator for tracking the diurnal variations in photosynthetically active radiation (PAR) and seasonal variations in GPP. For the O2–A band in particular, a high correlation coefficient value of 0.81 is found between the SIF and seasonal variations of GPP. It is thus concluded that, in coordination with continuous eddy covariance (EC) flux measurements, automated and continuous SIF observations can provide a reliable approach for understanding the photosynthetic activity of the terrestrial ecosystem, and are also able to bridge the link between ground-based optical measurements and airborne or satellite remote sensing data.
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Virtanen, Ilpo, and Kalevi Mursula. "Photospheric and coronal magnetic fields in six magnetographs." Astronomy & Astrophysics 626 (June 2019): A67. http://dx.doi.org/10.1051/0004-6361/201935713.
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Context. Solar photospheric magnetic fields have been observed since the 1950s and calibrated digital data are available from the 1970s onwards. Synoptic maps of the photospheric magnetic field are widely used in solar research, especially in the modeling of the solar corona and solar wind, and in studies of space weather and space climate. Magnetic flux density of the solar corona is a key parameter for heliospheric physics. Aims. The observed photospheric magnetic flux depends on the instrument and data processing used, which is a major problem for long-term studies. Here we scale the different observations of the photospheric field to the same absolute level and form a uniform record of coronal magnetic flux since the 1970s. Methods. We use a recently suggested method of harmonic scaling, which scales any pair of synoptic observations of any resolution to the same level. After scaling, we use the Potential Field Source Surface (PFSS) model to calculate the scaled magnetic field at various altitudes from photosphere to coronal source surface. Results. Harmonic scaling gives effective, latitudinally dependent scaling factors, which vary over the solar cycle. When scaling low-resolution data to high-resolution data, effective scaling factors are typically largest at low latitudes in the ascending phase of solar cycle and smallest for unipolar polar fields around solar minima. The harmonic scaling method used here allows for the observations of the different data sets to be scaled to the same level and the scaled unsigned coronal flux densities agree very well with each other. We also find that scaled coronal magnetic fields show a slightly different solar cycle variation from that of the nonscaled fields.
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Akulova, O. B., V. I. Bukaty, A. A. Vagner, A. V. Dyachenko, A. A. Kolomeytsev, and A. T. Zinoviev. "Photosynthetic Active Solar Radiation in Lake Teletskoye During the Open Water Period." Izvestiya of Altai State University, no. 4(126) (September 9, 2022): 11–17. http://dx.doi.org/10.14258/izvasu(2022)4-01.
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Spatial and temporal variability of flux density of photosynthetic active solar radiation (PAR) in the waters of large deep-water oligotrophic Lake Teletskoye (Republic of Altai) is considered based on the analyzed experimental data for the years 2016-2021. Probing of the lake water column was implemented using Satlanic PAR sensor as a part of CTD of the SBE 25plus probe at the beginning and the end of the summer heating period. During various years of studying, PAR magnitude monotonically decreased with lake depth increase and practically became zero at horizons from 3 to 14,8 m according to the data received from two weather stations at the reservoir, i.e. in the pelagic zone of rivers Chulyshman and Kokshi. Flux density of photosynthetic active solar radiation in the upper layer made up to 27-1000 μmol/(m2·s) during the observation period. The photic depth zone (at one percent irradiation) in Lake Teletskoye at the Chulyshman station on sunny days reached 14.8 m, while at the Kokshi one — 11.7 m. According to PAR measurements, the attenuation coefficient (extinction coefficient) along the vertical was estimated as 0.1-2.6 m-1. The maximum weakening coefficient at the Chulyshman station was recorded in June 2016 in the surface 3-m layer of the lake (1.8-2.6 m-1), while below 3 m it had values of 0.1-1.9 m-1. The attenuation coefficient varied within 0.1-1.6 m-1 at the Kokshi station. Relative transparency of the Secchi white disk at the Chulyshman and Kokshi stations ranged within 1.3-5.3 and 2.4-6.5 m, respectively. The paper also presents vertical lake profiles of water temperature in June-July — characteristic of direct summer stratification of the reservoir.
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Griboulard, Roger, Yann Deniaud, and Eliane Gonthier. "Observations des déformations superficielles par submersible et imagerie Sonar SAR d'un pli d'accrétion (prisme Sud-Barbade, océan Atlantique)." Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science 330, no. 4 (February 2000): 281–87. http://dx.doi.org/10.1016/s1251-8050(00)00128-2.
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Fragkos, Konstantinos, Ilias Fountoulakis, Georgia Charalampous, Kyriakoula Papachristopoulou, Argyro Nisantzi, Diofantos Hadjimitsis, and Stelios Kazadzis. "Twenty-Year Climatology of Solar UV and PAR in Cyprus: Integrating Satellite Earth Observations with Radiative Transfer Modeling." Remote Sensing 16, no. 11 (May 24, 2024): 1878. http://dx.doi.org/10.3390/rs16111878.
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In this study, we present comprehensive climatologies of effective ultraviolet (UV) quantities and photosynthetically active radiation (PAR) over Cyprus for the period 2004 to 2023, leveraging the synergy of earth observation (EO) data and radiative transfer model simulations. The EO dataset, encompassing satellite and reanalysis data for aerosols, total ozone column, and water vapor, alongside cloud modification factors, captures the nuanced dynamics of Cyprus’s atmospheric conditions. With a temporal resolution of 15 min and a spatial of 0.05° × 0.05°, these climatologies undergo rigorous validation against established satellite datasets and are further evaluated through comparisons with ground-based global horizontal irradiance measurements provided by the Meteorological Office of Cyprus. This dual-method validation approach not only underscores the models’ accuracy but also highlights its proficiency in capturing intra-daily cloud coverage variations. Our analysis extends to investigating the long-term trends of these solar radiation quantities, examining their interplay with changes in cloud attenuation, aerosol optical depth (AOD), and total ozone column (TOC). Significant decreasing trends in the noon ultraviolet index (UVI), ranging from −2 to −4% per decade, have been found in autumn, especially marked in the island’s northeastern part, mainly originating from the (significant) positive trends in TOC. The significant decreasing trends in TOC, of −2 to −3% per decade, which were found in spring, do not result in correspondingly significant positive trends in the noon UVI since variations in cloudiness and aerosols also have a strong impact on the UVI in this season. The seasonal trends in the day light integral (DLI) were generally not significant. These insights provide a valuable foundation for further studies aimed at developing public health strategies and enhancing agricultural productivity, highlighting the critical importance of accurate and high-resolution climatological data.
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Anshul, Pratyush, Anand Narayanan, Sowgat Muzahid, Alexander Beckett, and Simon L. Morris. "Pair lines of sight observations of multiphase gas bearing O vi in a galaxy environment." Monthly Notices of the Royal Astronomical Society 503, no. 3 (February 13, 2021): 3243–61. http://dx.doi.org/10.1093/mnras/stab396.
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ABSTRACT Using HST/COS spectra of the twin quasar lines of sight Q 0107–025A & Q 0107–025B, we report on the physical properties, chemical abundances, and transverse sizes of a multiphase medium in a galaxy field at z = 0.399. The angular separation between the quasars corresponds to a physical separation of 520 kpc at the absorber redshift. The absorber towards Q 0107–025B is a partial Lyman limit system (pLLS) with $\log N({\mathrm{H}}{\small I})/\hbox{cm$^{-2}$}\approx 16.8$. The H i column density in the absorber along the other sightline is ≈ 2 orders of magnitude lower. The O vi along both sightlines have comparable column densities and broad b-values (b > 30 km s−1) whereas the low ionization lines are considerably narrower. The low ionization gas is inconsistent with the O vi when modelled assuming photoionization from the same phase. In both lines of sight, O vi and the broad H i coinciding, are best explained through collisional ionization in a cooling plasma with solar metallicity. Ionization models infer 1/10th solar metallicity for the pLLS and solar metallicity for the lower column density absorber along the other sightline. Within ± 250 km s−1 and 2 Mpc of projected distance from the sightlines 12 galaxies are identified, of which five are within 500 kpc. The twin sightlines are at normalized impact parameters of ρ ∼ 1.1Rvir, and ρ ∼ 0.8Rvir from a M* ∼ 1010.7 M⊙, L ∼ 0.07L*, and star formation rate (SFR) < 0.1 M⊙ yr−1 galaxy, potentially probing its CGM (circumgalactic medium). The next closest in normalized separation are a dwarf galaxy with M* ∼ 108.7 M⊙, and SFR ∼ 0.06 M⊙ yr−1, and an intermediate mass galaxy with M* ∼ 1010.0 M⊙, and SFR ∼ 3 M⊙ yr−1. Along both sightlines, O vi could be either tracing narrow transition temperature zones at the interface of low ionization gas and the hot halo of nearest galaxy, or a more spread-out warm component that could be gas bound to the circumgalactic halo or the intragroup medium. The latter scenarios lead to a warm gas mass limit of M ≳ 4.5 × 109 M⊙.
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Choi, Yeji, Sujin Park, Soojin Kim, Eunsoo Kim, and Geonwoo Kim. "A Model Combining Forest Environment Images and Online Microclimate Data Instead of On-Site Measurements to Predict Phytoncide Emissions." Forests 13, no. 11 (November 11, 2022): 1895. http://dx.doi.org/10.3390/f13111895.
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In the existing phytoncide-prediction process, solar radiation and photosynthetically active radiation (PAR) are difficult microclimate factors to measure on site. We derived a phytoncide-prediction technique that did not require field measurements. Visual indicators extracted from forest images and statistical analysis were used to determine appropriate positioning for forest environment photography to improve the accuracy of the new phytoncide-prediction formula without using field measurements. Indicators were selected from the Automatic Mountain Meteorology Observation System (AMOS) of the Korea Forest Service to replace on-site measured climate data and the phytoncide-prediction equation was derived using them. Based on regression analyses, we found that forest density, leaf area, and light volume above the horizon could replace solar radiation and PAR. In addition, AMOS data obtained at 2 m altitudes yielded suitable variables to replace microclimate data measured on site. The accuracy of the new equation was highest when the surface area in the image accounted for 25% of the total. The new equation was found to have a higher prediction accuracy (71.1%) compared to that of the previous phytoncide-prediction equation (69.1%), which required direct field measurements. Our results allow the public to calculate and predict phytoncide emissions more easily in the future.
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Skeie, Kristian, and Arild Gustavsen. "Predicting solar radiation using a parametric cloud model." E3S Web of Conferences 172 (2020): 11006. http://dx.doi.org/10.1051/e3sconf/202017211006.
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In this paper, we evaluate a method to calculate hourly global solar radiation and improve the calculation of diffuse and vertical surface radiation on building facades by accounting for ground conditions based on publicly available data of cloud coverage, temperature and precipitation from a forecast service covering the Nordic countries. The detailed weather forecasts produced by MET Norway provide hourly forecasts for the next 60 hours, and 6-hour predictions for the next week. To calculate solar radiation on cloudy days the clear and cloudy sky MAC model developed by Davies and Mckay (1982) is used. Instead of basing the prediction on ground observations as in the original method, cloud coverage in three levels and total cloud cover is used as input in a cloud product parameterisation. The resulting global horizontal irradiance is validated against the output of the numerical weather prediction (NWP) model and compared to a year of hourly ground measurements in Trondheim, Norway. To evaluate applicability to the building sciences, vertical irradiance measurements are compared to tilted surface irradiance calculated with the ISO 52010:2017 method. For the location, six-hour forecasting performance is on par with the GHI output of the NWP model (using the cloud layer model and the available weather parameters of the location forecast API). To account for the unpredictability of clouds and improve the short-term forecasting performance beyond 38 % RMSD, 38 % SD and 0.80 R2 a different approach is needed, like combining model and sky observations.
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P, Hengjinda, and Joy Iong Zong Chen. "Renewable Energy Production from Agricultural Waste and Hydrogen Battery Formation." December 2020 2, no. 4 (February 9, 2021): 151–55. http://dx.doi.org/10.36548/jeea.2020.4.002.
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In recent years, the growth of solar and wind power installation has not grown in par with its electrical grid integration. Hence this proposed work uses frictional Pyrolysis to enable this integration by converting electrical energy into mechanical work without any indication of excess heat requirement. The renewable energy that is in excess can be used in conversion of agricultural residue to biocoal. This is the basis of of renewable battery. In this work a case study is presented such that biomass characteristics are examined and further transformed to bio coal. Observations indicate that in the past decade there is a significant increase in wind power installation (258%) and the number of solar PVs installed have also accounted for 21,437 GWh. From the biomass initial stage, the total amount of energy produced lies within the range 78% to 89%. This methodology of using renewable battery ensures that the environment state cleaner and carbon sequestration and also be implemented in agricultural development.
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Malandraki, O. E., R. G. Marsden, C. Tranquille, R. J. Forsyth, H. A. Elliott, and A. Geranios. "Energetic particle measurements from the <I>Ulysses</I>/COSPIN/LET instrument obtained during the August/September 2005 events." Annales Geophysicae 26, no. 4 (May 13, 2008): 1029–37. http://dx.doi.org/10.5194/angeo-26-1029-2008.
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Abstract. We report recent observations of energetic particles at energies 1–40 MeV/n made by the COSPIN/LET instrument onboard the Ulysses spacecraft during the period of intense solar activity in August/September 2005 during the declining phase of solar cycle 23. Ulysses, having started its climb to high southern latitudes for the third time, was located at ~5 AU, at a helio-latitude of ~30 degrees south. It detected the arrival of a solar wind compound stream resulting from the merging of a series of fast halo CMEs ejected from the Sun in late August and early September 2005 and their interaction with the pre-existing pattern of solar wind Stream Interaction Regions (SIRs) in the ambient medium through which they propagated. The heavy ion intensities are observed by COSPIN/LET to remain elevated for at least 20 days following the very intense X17.0/3B solar flare on 7 September and its associated very fast CME (plane of sky projected CME speed ~2400 km s−1). We carry out an analysis of the composition of the particle increases observed at the location of the spacecraft. Although the composition signatures were predominantly Solar Energetic Particle (SEP)-like, after the passage of the compound stream over Ulysses, in association with a characteristic forward and reverse shock pair, the observations showed evidence of an enhanced He content.
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Nair, P. J., S. Godin-Beekmann, J. Kuttippurath, G. Ancellet, F. Goutail, A. Pazmiño, L. Froidevaux, J. M. Zawodny, R. D. Evans, and M. Pastel. "Ozone trends derived from the total column and vertical profiles at a northern mid-latitude station." Atmospheric Chemistry and Physics Discussions 13, no. 3 (March 18, 2013): 7081–112. http://dx.doi.org/10.5194/acpd-13-7081-2013.
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Abstract. The trends and variability of ozone are assessed over a northern mid-latitude station, Haute-Provence Observatory (OHP – 43.93° N, 5.71° E), using total column ozone observations from the Dobson and Système d'Analyse par Observation Zénithale spectrometers, and stratospheric ozone profile measurements from Light detection and ranging, ozonesondes, Stratospheric Aerosol and Gas Experiment II, Halogen Occultation Experiment and Aura Microwave Limb Sounder. A multi-variate regression model with quasi biennial oscillation (QBO), solar flux, aerosol optical thickness, heat flux, North Atlantic oscillation (NAO) and piecewise linear trend (PWLT) or Equivalent Effective Stratospheric Chlorine (EESC) functions is applied to the ozone anomalies. The maximum variability of ozone in winter/spring is explained by QBO and heat flux in 15–45 km and in 15–24 km, respectively. The NAO shows maximum influence in the lower stratosphere during winter while the solar flux influence is largest in the lower and middle stratosphere in summer. The total column ozone trends estimated from the PWLT and EESC functions are of −1.39±0.26 and −1.40±0.25 DU yr−1, respectively over 1984–1996 and about 0.65±0.32 and 0.42±0.08 DU yr−1, respectively over 1997–2010. The ozone profiles yield similar and significant EESC-based and PWLT trends in 1984–1996 and are about −0.5 and −0.8 % yr−1 in the lower and upper stratosphere, respectively. In 1997–2010, the EESC-based and PWLT trends are significant and of order 0.3 and 0.1 % yr−1, respectively in the 18–28 km range, and at 40–45 km, EESC provides significant ozone trends larger than the insignificant PWLT results. Therefore, this analysis unveils ozone recovery signals from total column ozone and profile measurements at OHP, and hence in the mid-latitudes.
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Efimenko, V., and V. Krivodubskij. "Life and scientific way of Pavlo Rodionovych Romanchuk." Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 61 (2020): 28–33. http://dx.doi.org/10.17721/btsnua.2020.61.28-33.
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One hundred years have passed since the birth of P.R. Romanchuk – Hero of the Soviet Union, Candidate of Physical and Mathematical Sciences, Associate Professor, Director of the Astronomical Observatory (1972–1987). At his initiative, the observatory began to develop new scientific directions: theoretical research of magnetic fields and the beginning of experimental work after the purchase of a magnetograph, study of changes in the solar atmosphere associated with flare activity, solar-terrestrial connections and the impact of solar activity on weather phenomena, development of methods for predicting solar activity. An important result of his work was the strengthening of the observatory’s material base – purchase of a purchase of a magnetograph, modernization of a horizontal solar telescope, joint work with the National Academy of Sciences of Ukraine on the development and manufacture of an axial meridian circle, purchase of equipment for television observations of meteors.
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Beniyama, Jin, Shigeyuki Sako, Katsuhito Ohtsuka, Tomohiko Sekiguchi, Masateru Ishiguro, Daisuke Kuroda, Seirato Urakawa, et al. "Photometry and Polarimetry of 2010 XC15: Observational Confirmation of E-type Near-Earth Asteroid Pair." Astrophysical Journal 955, no. 2 (September 27, 2023): 143. http://dx.doi.org/10.3847/1538-4357/ace88f.
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Abstract Asteroid systems such as binaries and pairs are indicative of the physical properties and dynamical histories of small solar system bodies. Although numerous observational and theoretical studies have been carried out, the formation mechanism of asteroid pairs is still unclear, especially for near-Earth asteroid (NEA) pairs. We conducted a series of optical photometric and polarimetric observations of a small NEA 2010 XC15 in 2022 December to investigate its surface properties. The rotation period of 2010 XC15 is possibly a few to several dozen hours and the color indices of 2010 XC15 are derived as g − r = 0.435 ± 0.008, r − i = 0.158 ± 0.017, and r − z = 0.186 ± 0.009 in the Pan-STARRS system. The linear polarization degrees of 2010 XC15 are a few percent at the phase angle range of 58°–114°. We found that 2010 XC15 is a rare E-type NEA on the basis of its photometric and polarimetric properties. Taking the similarity of not only physical properties but also dynamical integrals and the rarity of E-type NEAs into account, we suppose that 2010 XC15 and 1998 WT24 are of common origin (i.e., an asteroid pair). These two NEAs are the sixth NEA pair and first E-type NEA pair ever confirmed, possibly formed by rotational fission. We conjecture that the parent body of 2010 XC15 and 1998 WT24 was transported from the main belt through the ν 6 resonance or Hungaria region.
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Singh, Rakesh Kumar, Anna Vader, Christopher J. Mundy, Janne E. Søreide, Katrin Iken, Kenneth H. Dunton, Laura Castro de la Guardia, Mikael K. Sejr, and Simon Bélanger. "Satellite-Derived Photosynthetically Available Radiation at the Coastal Arctic Seafloor." Remote Sensing 14, no. 20 (October 17, 2022): 5180. http://dx.doi.org/10.3390/rs14205180.
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Climate change has affected the Arctic Ocean (AO) and its marginal seas significantly. The reduction of sea ice in the Arctic region has altered the magnitude of photosynthetically available radiation (PAR) entering the water column, impacting primary productivity. Increasing cloudiness in the atmosphere and rising turbidity in the coastal waters of the Arctic region are considered as the major factors that counteract the effect of reduced sea ice on underwater PAR. Additionally, extreme solar zenith angles and sea-ice cover in the AO increase the complexity of retrieving PAR. In this study, a PAR algorithm based on radiative transfer in the atmosphere and satellite observations is implemented to evaluate the effect of these factors on PAR in the coastal AO. To improve the performance of the algorithm, a flag is defined to identify pixels containing open-water, sea-ice or cloud. The use of flag enabled selective application of algorithms to compute the input parameters for the PAR algorithm. The PAR algorithm is validated using in situ measurements from various coastal sites in the Arctic and sub-Arctic seas. The algorithm estimated daily integrated PAR above the sea surface with an uncertainty of 19% in summer. The uncertainty increased to 24% when the algorithm was applied year-round. The PAR values at the seafloor were estimated with an uncertainty of 76%, with 36% of the samples under sea ice and/or cloud cover. The robust performance of the PAR algorithm in the pan-Arctic region throughout the year will help to effectively study the temporal and spatial variability of PAR in the Arctic coastal waters. The calculated PAR data are used to quantify the changing trend in PAR at the seafloor in the coastal AO with depth < 100 m using MODIS-Aqua data from 2003 to 2020. The general trends calculated using the pixels with average PAR > 0.415 mol m−2day−1 at the seafloor during summer indicate that the annual average of PAR entering the water column in the coastal AO between 2003 and 2020 increased by 23%. Concurrently, due to increased turbidity, the attenuation in the water column increased by 22%. The surge in incident PAR in the water column due to retreating sea ice first led to increased PAR observed at the seafloor (∼12% between 2003 and 2014). However, in the last decade, the rapid increase in light attenuation of the water column has restricted the increase in average annual PAR reaching the bottom in the coastal AO.
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Song, Xiaojian, Xi Luo, Marius S. Potgieter, XinMing Liu, and Zekun Geng. "A Numerical Study of the Solar Modulation of Galactic Protons and Helium from 2006 to 2017." Astrophysical Journal Supplement Series 257, no. 2 (December 1, 2021): 48. http://dx.doi.org/10.3847/1538-4365/ac281c.
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Abstract With continuous measurements from space-borne cosmic-ray detectors such as AMS-02 and PAMELA, precise spectra of galactic cosmic rays over the 11 yr solar cycle have become available. For this study, we utilize proton and helium spectra below 10 GV from these missions from 2006 to 2017 to construct a cosmic-ray transport model for a quantitative study of the processes of solar modulation. This numerical model is based on Parker’s transport equation, which includes four major transport processes. The Markov Chain Monte Carlo method is utilized to search the relevant parameter space related to the drift and the diffusion coefficients by reproducing and fitting the mentioned observed spectra. The resulting best-fit normalized χ 2 is mainly less than 1. It is found that (1) when reproducing these observations the parameters required for the drift and diffusion coefficients exhibit a clear time dependence, with the magnitude of the diffusion coefficients anticorrelated with solar activity; (2) the rigidity dependence of the resulting mean free paths varies with time, and their rigidity dependence at lower rigidity can even have a larger slope than at higher rigidity; (3) using a single set of modulation parameters for each pair of observed proton and helium spectra, most spectra are reproduced within observational uncertainty; and (4) the simulated proton-to-helium flux ratio agrees with the observed values in terms of its long-term time dependence, although some discrepancy exists, and the difference is mostly coming from the underestimation of proton flux.