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1
CHRISTENSEN, C. WIIN, and A. WIIN-NIELSEN. "Blocking as a wave-wave interaction." Tellus A 48, no. 2 (March 1996): 254–71. http://dx.doi.org/10.1034/j.1600-0870.1996.t01-1-00005.x.
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Christensen, C. Wün, and A. Wiin-Nielsen. "Blocking as a wave—wave interaction." Tellus A: Dynamic Meteorology and Oceanography 48, no. 2 (January 1996): 254–71. http://dx.doi.org/10.3402/tellusa.v48i2.12059.
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Yang, Xiaoye, Gang Zeng, Guwei Zhang, Jingwei Li, Zhongxian Li, and Zhixin Hao. "Interdecadal Variations of Different Types of Summer Heat Waves in Northeast China Associated with AMO and PDO." Journal of Climate 34, no. 19 (October 2021): 7783–97. http://dx.doi.org/10.1175/jcli-d-20-0939.1.
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AbstractThe summer heat waves (HWs) in Northeast China (NEC) during 1961–2016 can be classified into two types, namely, wave train HWs and blocking HWs based on the hierarchical clustering algorithm by using ERA-Interim daily datasets. Wave train HWs occurred accompanied by eastward-moving wave trains with a “− + − +” structure formed over Eurasia, while the blocking HWs occurred with blocking circulation anomalies over Eurasia. In general, the blocking HWs could cause the positive temperature anomalies in NEC to last longer than wave train HWs. During the period from 1961 to 2016, the wave train HWs experienced an interdecadal variation from less to more, while the blocking HWs experienced interdecadal variations of less–more–less. Regression analysis and information flow indicate that the interdecadal variation of the wave train HWs is associated with Atlantic multidecadal oscillation (AMO) and Pacific decadal oscillation (PDO), while the interdecadal variation of the blocking HWs is more likely associated with PDO. The positive phase of AMO (negative phase of PDO) could increase the wave train (blocking) HWs by strengthening the zonal wave train similar to the Silk Road pattern (the arched wave train like the polar–Eurasian pattern). The observed results are in agreement with the numerical experiments with the NCAR Community Atmosphere Model, version 5.3.
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Moreira, R. M., and D. H. Peregrine. "Nonlinear interactions between deep-water waves and currents." Journal of Fluid Mechanics 691 (December 6, 2011): 1–25. http://dx.doi.org/10.1017/jfm.2011.436.
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AbstractThe effects of nonlinearity on a train of linear water waves in deep water interacting with underlying currents are investigated numerically via a boundary-integral method. The current is assumed to be two-dimensional and stationary, being induced by a distribution of singularities located beneath the free surface, which impose sharp and gentle surface velocity gradients. For ‘slowly’ varying currents, the fully nonlinear results confirm that opposing currents induce wave steepening and breaking within the region where a high convergence of rays occurs. For ‘rapidly’ varying currents, wave blocking and breaking are more prominent. In this case reflection was observed when sufficiently strong adverse currents are imposed, confirming that at least part of the wave energy that builds up within the caustic can be released in the form of partial reflection and wave breaking. For bichromatic waves, the fully nonlinear results show that partial wave blocking occurs at the individual wave components in the wave groups and that waves become almost monochromatic upstream of the blocking region.
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Yang, Guoliang, Shuai Feng, and Wenjia Huang. "Wave-Blocking Characteristics of Corrugated Plates under Explosion." Shock and Vibration 2020 (February 29, 2020): 1–8. http://dx.doi.org/10.1155/2020/5895812.
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Corrugated-board explosion-proof wall is the main means to prevent explosion shock wave damage, and it is important to study the effect of different corrugated plates on the shock wave. Using a high-speed schlieren experimental system and an air overpressure test system, the wave-blocking characteristics of different forms of corrugated plates are comprehensively studied. The schlieren images were used to analyze the influence that the corrugation shape of a corrugated plate has on the shock wave propagation characteristics. The results show that the reflection process of the triangular-, trapezoidal-, and half-cylindrical-shaped corrugated plates exhibit differences. The number of reflected waves from the triangular corrugated plate is much greater than that from the other corrugated plates, and it will consume more energy. The diffraction wave-front velocity has a trend of initially decreasing and then increasing and is also reduced by different degrees by the reflection. Comparative analysis of the schlieren images and the air shock wave overpressure test shows that plates corrugated with different corrugation shapes decrease the diffraction overpressure peak and exhibit a hysteresis.
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Luo, Dehai, and Wenqi Zhang. "A Nonlinear Multiscale Theory of Atmospheric Blocking: Eastward and Upward Propagation and Energy Dispersion of Tropospheric Blocking Wave Packets." Journal of the Atmospheric Sciences 77, no. 12 (December 2020): 4025–49. http://dx.doi.org/10.1175/jas-d-20-0153.1.
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AbstractIn this paper, a nonlinear multiscale interaction model is used to examine how the planetary waves associated with eddy-driven blocking wave packets propagate through the troposphere in vertically varying weak baroclinic basic westerly winds (BWWs). Using this model, a new one-dimensional finite-amplitude local wave activity flux (WAF) is formulated, which consists of linear WAF related to linear group velocity and local eddy-induced WAF related to the modulus amplitude of blocking envelope amplitude and its zonal nonuniform phase. It is found that the local eddy-induced WAF reduces the divergence (convergence) of linear WAF in the blocking upstream (downstream) side to favor blocking during the blocking growth phase. But during the blocking decay phase, enhanced WAF convergence occurs in the blocking downstream region and in the upper troposphere when BWW is stronger in the upper troposphere than in the lower troposphere, which leads to enhanced upward-propagating tropospheric wave activity, though the linear WAF plays a major role. In contrast, the downward propagation of planetary waves may be seen in the troposphere for vertically decreased BWWs. These are not seen for a zonally uniform eddy forcing. A perturbed inverse scattering transform method is used to solve the blocking envelope amplitude equation. It is found that the finite-amplitude WAF represents a modified group velocity related to the variations of blocking soliton amplitude and zonal wavenumber caused by local eddy forcing. Using this amplitude equation solution, it is revealed that, under local eddy forcing, the blocking wave packet tends to be nearly nondispersive during its growth phase but strongly dispersive during the decay phase for vertically increased BWWs, leading to strong eastward and upward propagation of planetary waves in the downstream troposphere.
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Moreira, R. M., and J. T. A. Chacaltana. "Vorticity effects on nonlinear wave–current interactions in deep water." Journal of Fluid Mechanics 778 (July 31, 2015): 314–34. http://dx.doi.org/10.1017/jfm.2015.385.
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The effects of uniform vorticity on a train of ‘gentle’ and ‘steep’ deep-water waves interacting with underlying flows are investigated through a fully nonlinear boundary integral method. It is shown that wave blocking and breaking can be more prominent depending on the magnitude and direction of the shear flow. Reflection continues to occur when sufficiently strong adverse currents are imposed on ‘gentle’ deep-water waves, though now affected by vorticity. For increasingly positive values of vorticity, the induced shear flow reduces the speed of right-going progressive waves, introducing significant changes to the free-surface profile until waves are completely blocked by the underlying current. A plunging breaker is formed at the blocking point when ‘steep’ deep-water waves interact with strong adverse currents. Conversely negative vorticities augment the speed of right-going progressive waves, with wave breaking being detected for strong opposing currents. The time of breaking is sensitive to the vorticity’s sign and magnitude, with wave breaking occurring later for negative values of vorticity. Stopping velocities according to nonlinear wave theory proved to be sufficient to cause wave blocking and breaking.
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Wen, Hua Bing, Lin Bo Liu, Zi Long Peng, and Qi Dong Zhong. "Research on the Effects of Blocking Mass on Vibration Resistance Performance of L-Shaped Plates." Applied Mechanics and Materials 482 (December 2013): 131–35. http://dx.doi.org/10.4028/www.scientific.net/amm.482.131.
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The theory of vibration resistance of blocking mass at the corner interface of L-shaped plates is put forward from the perspective of wave approach. The equation of transmission and reflection coefficients of flexure wave is deduced by the presented theory. Based on FE/SEA method, the vibration resistance performance of the hollow blocking mass at the corner interface of L-shaped plates was studied through numerical simulation. The results show that the hollow blocking mass can impede the propagation of the high frequency vibration waves, reduce the vibration and sound radiation of the latter plate, and increase the influence of the reflection waves on the former plate. However, the overall radiant energy is basically identical to the L-shaped plates without the hollow blocking mass.
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Xu, Ying, Wuyin Jin, and Jun Ma. "Emergence and robustness of target waves in a neuronal network." International Journal of Modern Physics B 29, no. 23 (September 17, 2015): 1550164. http://dx.doi.org/10.1142/s0217979215501647.
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Target waves in excitable media such as neuronal network can regulate the spatial distribution and orderliness as a continuous pacemaker. Three different schemes are used to develop stable target wave in the network, and the potential mechanism for emergence of target waves in the excitable media is investigated. For example, a local pacing driven by external periodical forcing can generate stable target wave in the excitable media, furthermore, heterogeneity and local feedback under self-feedback coupling are also effective to generate continuous target wave as well. To discern the difference of these target waves, a statistical synchronization factor is defined by using mean field theory and artificial defects are introduced into the network to block the target wave, thus the robustness of these target waves could be detected. However, these target waves developed from the above mentioned schemes show different robustness to the blocking from artificial defects. A regular network of Hindmarsh–Rose neurons is designed in a two-dimensional square array, target waves are induced by using three different ways, and then some artificial defects, which are associated with anatomical defects, are set in the network to detect the effect of defects blocking on the travelling waves. It confirms that the robustness of target waves to defects blocking depends on the intrinsic properties (ways to generate target wave) of target waves.
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Berrisford, P., B. J. Hoskins, and E. Tyrlis. "Blocking and Rossby Wave Breaking on the Dynamical Tropopause in the Southern Hemisphere." Journal of the Atmospheric Sciences 64, no. 8 (August 2007): 2881–98. http://dx.doi.org/10.1175/jas3984.1.
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Rossby wave breaking on the dynamical tropopause in the Southern Hemisphere (the −2-PVU surface) is investigated using the ERA-40 dataset. The indication of wave breaking is based on reversal in the meridional gradient of potential temperature, and persistent large-scale wave breaking is taken as a strong indication that blocking may be present. Blocking in the midlatitudes is found to occur predominantly during wintertime in the Pacific and is most vigorous in the east Pacific, while during summertime, the frequency of blocking weakens and its extent becomes confined to the west Pacific. The interannual variability of blocking is found to be high. Wave breaking occurs most frequently on the poleward side of the polar jet and has some, but not all, of the signatures of blocking, so it is referred to as high-latitude blocking. In general, cyclonic wave breaking occurs on the poleward side of the polar jet, otherwise anticyclonic breaking occurs. However, at least in wintertime, wave breaking in the New Zealand/west to mid-Pacific sector between the polar and subtropical jets is a mixture between cyclonic and anticyclonic types. Together, episodes of wave breaking and enhanced westerly flow describe much of the variability in the seasonal Antarctic Oscillation (AnO) index and give a synoptic manifestation of it with a focus on the date line and Indian Ocean that is in agreement with the centers of action for the AnO. During summertime, anticyclonic wave breaking in the upper troposphere is also to be found near 30°S in both the Pacific and Atlantic, and appears to be associated with Rossby waves propagating into the subtropics from the New Zealand region.
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McHall, Yong L. "Nonlinear planetary wave instability and blocking." Advances in Atmospheric Sciences 9, no. 2 (June 1992): 173–90. http://dx.doi.org/10.1007/bf02657508.
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Masato, G., B. J. Hoskins, and T. J. Woollings. "Wave-breaking characteristics of midlatitude blocking." Quarterly Journal of the Royal Meteorological Society 138, no. 666 (December 12, 2011): 1285–96. http://dx.doi.org/10.1002/qj.990.
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Chatterjee, Debasmita, B. S. Mazumder, and Subir Ghosh. "Turbulence characteristics of wave-blocking phenomena." Applied Ocean Research 75 (June 2018): 15–36. http://dx.doi.org/10.1016/j.apor.2018.03.011.
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Luo, Dehai. "A Barotropic Envelope Rossby Soliton Model for Block–Eddy Interaction. Part II: Role of Westward-Traveling Planetary Waves." Journal of the Atmospheric Sciences 62, no. 1 (January 1, 2005): 22–40. http://dx.doi.org/10.1175/3347.1.
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Abstract The role of westward-traveling planetary waves in the block onset and the deformation of eddies during the interaction between synoptic-scale eddies and an incipient block is first examined by constructing an incipient block that consists of a stationary dipole wave for zonal wavenumber 2 and a westward-traveling monopole wave with constant amplitude (C wave) for zonal wavenumber 1 or 2. It is shown that the C-wave can affect the onset and strength of blocking through influencing the preblock (diffluent) flow even though it does not affect the amplification of the dipole wave associated with the synoptic-scale eddies. Whether the storm tracks organized by the deformed eddies deflect northward depends upon the zonal wavenumber, amplitude, and phase of the C wave relative to the stationary dipole wave. A typical retrograde blocking anticyclone can arise through the interaction of an incipient block with synoptic-scale perturbations when the C-wave ridge with zonal wavenumber 1 shifts westward from the east of the dipole wave in an incipient block. In this process, a slight northward deflection of organized storm tracks is also observed, particularly under the condition of a large-amplitude C wave. In addition, the interaction between a diffluent flow, consisting of a coupled dipole and monopole waves, and upstream synoptic-scale eddies is investigated. It is found that the eddy forcing tends to not only periodically amplify the dipole soliton and to retard its eastward movement, but to make the monopole wave break up. The breaking of the traveling monopole wave will suppress the eddy-induced blocking ridge that exhibits a surf zone structure where the negative meridional gradient of planetary-scale potential vorticity exists and cause the planetary-scale blocking field to lose its closed circulation compared to that without coupling.
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Paradise, Adiv, Cesar B. Rocha, Pragallva Barpanda, and Noboru Nakamura. "Blocking Statistics in a Varying Climate: Lessons from a “Traffic Jam” Model with Pseudostochastic Forcing." Journal of the Atmospheric Sciences 76, no. 10 (September 12, 2019): 3013–27. http://dx.doi.org/10.1175/jas-d-19-0095.1.
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Abstract Recently Nakamura and Huang proposed a semiempirical, one-dimensional model of atmospheric blocking based on the observed budget of local wave activity in the boreal winter. The model dynamics is akin to that of traffic flow, wherein blocking manifests as traffic jams when the streamwise flux of local wave activity reaches capacity. Stationary waves modulate the jet stream’s capacity to transmit transient waves and thereby localize block formation. Since the model is inexpensive to run numerically, it is suited for computing blocking statistics as a function of climate variables from large-ensemble, parameter sweep experiments. We explore sensitivity of blocking statistics to (i) stationary wave amplitude, (ii) background jet speed, and (iii) transient eddy forcing, using frequency, persistence, and prevalence as metrics. For each combination of parameters we perform 240 runs of 180-day simulations with aperiodic transient eddy forcing, each time randomizing the phase relations in forcing. The model climate shifts rapidly from a block-free state to a block-dominant state as the stationary wave amplitude is increased and/or the jet speed is decreased. When eddy forcing is increased, prevalence increases similarly but frequency decreases as blocks merge and become more persistent. It is argued that the present-day climate lies close to the boundary of the two states and hence its blocking statistics are sensitive to climate perturbations. The result underscores the low confidence in GCM-based assessment of the future trend of blocking under a changing climate, while it also provides a theoretical basis for evaluating model biases and understanding trends in reanalysis data.
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Singla, Parveen, Shabnam Thakur, Rinkesh Mittal, and Mohit Srivastava. "Millimeter Wave Communication for 5G Networks." CGC International Journal of Contemporary Technology and Research 3, no. 2 (July 17, 2021): 196–98. http://dx.doi.org/10.46860/cgcijctr.2021.06.31.196.
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The severe increase in the number of consumers in wireless technology has caused traffic processing problems, so the mobile data growth needs a super-productive mobile network. In upcoming 5G technology, that provides faster data rates, low latency; better service quality and greater capacity have emerged. Different frequencies are used to transmit and receive data via radio waves. Between conventional and millimeter wave communications, it is considered that there are essential differences in directivity, sensitivity to blocking and high propagation loss. On some issues, millimeter wave brings various challenges in communication, such as ant blocking, interference management, space reuse etc. The main focus of this paper is to present 5G’s characteristics wave communication and discussing the use of available bandwidth in millimeter wave spectrum carefully and the benefit to next generation mobile users.
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Narinesingh, Veeshan, James F. Booth, Spencer K. Clark, and Yi Ming. "Atmospheric blocking in an aquaplanet and the impact of orography." Weather and Climate Dynamics 1, no. 2 (July 8, 2020): 293–311. http://dx.doi.org/10.5194/wcd-1-293-2020.
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Abstract. Many fundamental questions remain about the roles and effects of stationary forcing on atmospheric blocking. As such, this work utilizes an idealized moist general circulation model (GCM) to investigate atmospheric blocking in terms of dynamics, geographical location, and duration. The model is first configured as an aquaplanet, then orography is added in separate integrations. Block-centered composites of wave activity fluxes and height show that blocks in the aquaplanet undergo a realistic dynamical evolution when compared to reanalysis. Blocks in the aquaplanet are also found to have similar life cycles to blocks in model integrations with orography. These results affirm the usefulness of both zonally symmetric and asymmetric idealized model configurations for studying blocking. Adding orography to the model leads to an increase in blocking. This mirrors what is observed when comparing the Northern Hemisphere (NH) and Southern Hemisphere (SH), where the NH contains more orography and thus more blocking. As the prescribed mountain height increases, so do the magnitude and size of climatological stationary waves, resulting in more blocking overall. Increases in blocking, however, are not spatially uniform. Orography is found to induce regions of enhanced block frequency just upstream of mountains, near high pressure anomalies in the stationary waves, which is poleward of climatological minima in upper-level zonal wind, while block frequency minima and jet maxima occur eastward of the wave trough. This result matches what is observed near the Rocky Mountains. Finally, an analysis of block duration suggests blocks generated near stationary wave maxima last slightly longer than blocks that form far from or without orography. Overall, the results of this work help to explain some of the observed similarities and differences in blocking between the NH and SH and emphasize the importance of general circulation features in setting where blocks most frequently occur.
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Nakamura, Noboru, and Clare S. Y. Huang. "Atmospheric blocking as a traffic jam in the jet stream." Science 361, no. 6397 (May 24, 2018): 42–47. http://dx.doi.org/10.1126/science.aat0721.
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Atmospheric blocking due to anomalous, persistent meandering of the jet stream often causes weather extremes in the mid-latitudes. Despite the ubiquity of blocking, the onset mechanism is not well understood. Here we demonstrate a close analogy between blocking and traffic congestion on a highway by using meteorological data and show that blocking and traffic congestion can be described by a common mathematical theory. The theory predicts that the jet stream has a capacity for the flux of wave activity (a measure of meandering), just as the highway has traffic capacity, and when the capacity is exceeded, blocking manifests as congestion. Stationary waves modulate the jet stream’s capacity for transient waves and localize block formation. Climate change likely affects blocking frequency by modifying the jet stream’s proximity to capacity.
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Hsu, Wen-Yang, Igor Shugan, Wen-Son Chiang, Ray-Yeng Yang, Hwung-Hweng Hwung, Sergey Kuznetsov, and Yana Saprykina. "AN EXPERIMENTAL STUDY ON NONLINEAR WAVE DYNAMICS: ROUGE WAVE GENERATION AND WAVE BLOCKING." Coastal Engineering Proceedings 1, no. 34 (October 26, 2014): 34. http://dx.doi.org/10.9753/icce.v34.waves.34.
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G. Aronson, D., N. V. Mantzaris, and Hans Othmer. "Wave propagation and blocking in inhomogeneous media." Discrete & Continuous Dynamical Systems - A 13, no. 4 (2005): 843–76. http://dx.doi.org/10.3934/dcds.2005.13.843.
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Li, Huoqing, Junjian Liu, Hailiang Zhang, Chenxiang Ju, Junjie Shi, Junlan Zhang, Ali Mamtimin, and Shuiyong Fan. "Performance Evaluation of Sub-Grid Orographic Parameterization in the WRF Model over Complex Terrain in Central Asia." Atmosphere 11, no. 11 (October 28, 2020): 1164. http://dx.doi.org/10.3390/atmos11111164.
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The terrain of Central Asia is complex and rugged over mountains. Consequently, wind speed is overestimated over mountains and plains when using the Weather Research Forecast (WRF) model in winter. To solve this problem, three different simulations (named as control simulation (CRTL), gravity waves (GWD), and flow-blocking drag (FBD), respectively) were designed to investigate the impact of sub-grid orography (gravity waves and flow-blocking drag) on wind forecasts. The results illustrated that near-surface wind-speed overestimations were alleviated when sub-grid orographic drag was used in GWD, though the upper-level wind fields at 500 hPa were excessively reduced compared to CRTL. Thus, we propose eliminating the gravity wave breaking at the upper level to improve upper-level wind underestimations and surface wind speeds at the same time. The sub-grid orographic drag stress of the vertical profile over mountains was reduced when only the flow-blocking drag was retained in FBD. This alleviated underestimations of the upper-level wind speed and near-surface wind, which both have the same positive effects as the gravity wave and flow-blocking total. The mean bias and root mean squared error reduced by 32.76% and 9.39%, respectively, compared to CRTL. Moreover, the temperature and specific humidity in the lower troposphere were indirectly improved. The results of the study demonstrate that it is better to remove sub-grid orographic gravity wave drag when using the gravity wave drag scheme of the WRF model.
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Melito, Lorenzo, Matteo Postacchini, Alex Sheremet, Joseph Calantoni, Gianluca Zitti, Giovanna Darvini, and Maurizio Brocchini. "Wave-Current Interactions and Infragravity Wave Propagation at a Microtidal Inlet." Proceedings 2, no. 11 (August 2, 2018): 628. http://dx.doi.org/10.3390/proceedings2110628.
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Recent studies have shown that wave blocking occurs at river mouths with strong currents typically preventing relatively short period sea and swell waves from propagating up the river. However, observations demonstrate that lower frequency waves, so-called infragravity waves, do pass through and propagate up the river, particularly during storm events. We present observations from the Misa River estuary of infragravity wave propagation up the river during storm conditions. A model of the complex nonlinear interactions that drive infragravity waves is presented. The results are discussed in the context of an observed river mouth bar formed in the lower reach of the Misa River.
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Das, S., T. Sahoo, and M. H. Meylan. "Flexural-gravity wave dynamics in two-layer fluid: blocking and dead water analogue." Journal of Fluid Mechanics 854 (August 31, 2018): 121–45. http://dx.doi.org/10.1017/jfm.2018.617.
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Flexural-gravity wave characteristics are analysed, in the presence of a compressive force and a two-layer fluid, under the assumption of linearized water wave theory and small amplitude structural response. The occurrence of blocking for flexural-gravity waves is demonstrated in both the surface and internal modes. Within the threshold of the blocking and the buckling limit, the dispersion relation possesses four positive roots (for fixed wavenumber). It is shown that, under certain conditions, the phase and group velocities coalesce. Moreover, a wavenumber range for certain critical values of compression and depth is provided within which the internal wave energy moves faster than that of the surface wave. It is also demonstrated that, for shallow water, the wave frequencies in the surface and internal modes will never coalesce. It is established that the phase speed in the surface and internal modes attains a minimum and maximum, respectively, when the interface is located approximately in the middle of the water depth. An analogue of the dead water phenomenon, the occurrence of a high amplitude internal wave with a low amplitude at the surface, is established, irrespective of water depth, when the densities of the two fluids are close to each other. When the interface becomes close to the seabed, the dead water effect ceases to exist. The theory developed in the frequency domain is extended to the time domain and examples of negative energy waves and blocking are presented.
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Schneidereit, Andrea, Silke Schubert, Pavel Vargin, Frank Lunkeit, Xiuhua Zhu, Dieter H. W. Peters, and Klaus Fraedrich. "Large-Scale Flow and the Long-Lasting Blocking High over Russia: Summer 2010." Monthly Weather Review 140, no. 9 (September 1, 2012): 2967–81. http://dx.doi.org/10.1175/mwr-d-11-00249.1.
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Abstract Several studies show that the anomalous long-lasting Russian heat wave during the summer of 2010, linked to a long-persistent blocking high, appears mainly as a result of natural atmospheric variability. This study analyzes the large-scale flow structure based on the ECMWF Re-Analysis Interim (ERA-Interim) data (1989–2010). The anomalous long-lasting blocking high over western Russia including the heat wave occurs as an overlay of a set of anticyclonic contributions on different time scales. (i) A regime change in ENSO toward La Niña modulates the quasi-stationary wave structure in the boreal summer hemisphere supporting the eastern European blocking. The polar Arctic dipole mode is enhanced and shows a projection on the mean blocking high. (ii) Together with the quasi-stationary wave anomaly, the transient eddies maintain the long-lasting blocking. (iii) Three different pathways of wave action are identified on the intermediate time scale (~10–60 days). One pathway commences over the eastern North Pacific and includes the polar Arctic region; another one runs more southward and crossing the North Atlantic, continues to eastern Europe; a third pathway southeast of the blocking high describes the downstream development over South Asia.
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Rhines, P. B. "Jets and Orography: Idealized Experiments with Tip Jets and Lighthill Blocking." Journal of the Atmospheric Sciences 64, no. 10 (October 1, 2007): 3627–39. http://dx.doi.org/10.1175/jas4008.1.
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Abstract This paper describes qualitative features of the generation of jetlike concentrated circulations, wakes, and blocks by simple mountainlike orography, both from idealized laboratory experiments and shallow-water numerical simulations on a sphere. The experiments are unstratified with barotropic lee Rossby waves, and jets induced by mountain orography. A persistent pattern of lee jet formation and lee cyclogenesis owes its origins to arrested topographic Rossby waves above the mountain and potential vorticity (PV) advection through them. The wake jet occurs on the equatorward, eastern flank of the topography. A strong upstream blocking of the westerly flow occurs in a Lighthill mode of long Rossby wave propagation, which depends on βa2/U, the ratio of Rossby wave speed based on the scale of the mountain, to zonal advection speed, U (β is the meridional potential vorticity gradient, f is the Coriolis frequency, and a is the diameter of the mountain). Mountains wider (north–south) than the east–west length scale of stationary Rossby waves will tend to block the oncoming westerly flow. These blocks are essentially β plumes, which are illustrated by their linear Green function. For large βa2/U, upwind blocking is strong; the mountain wake can be unstable, filling the fluid with transient Rossby waves as in the numerical simulations of Polvani et al. For small values, βa2/U ≪ 1 classic lee Rossby waves with large wavelength compared to the mountain diameter are the dominant process. The mountain height, δh, relative to the mean fluid depth, H, affects these transitions as well. Simple lee Rossby waves occur only for such small heights, δh/h ≪ aβ/f, that the f/h contours are not greatly distorted by the mountain. Nongeostrophic dynamics are seen in inertial waves generated by geostrophic shear, and ducted by it, and also in a texture of finescale, inadvertent convection. Weakly damped circulations induced in a shallow-water numerical model on a sphere by a lone mountain in an initially simple westerly wind are also described. Here, with βa2/U ∼1, potential vorticity stirring and transient Rossby waves dominate, and drive zonal flow acceleration. Low-latitude critical layers, when present, exert strong control on the high-latitude waves, and with no restorative damping of the mean zonal flow, they migrate poleward toward the source of waves. While these experiments with homogeneous fluid are very simplified, the baroclinic atmosphere and ocean have many tall or equivalent barotropic eddy structures owing to the barotropization process of geostrophic turbulence.
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Giongo, Gabriel Augusto, José Valentin Bageston, Cosme Alexandre Oliveira Barros Figueiredo, Cristiano Max Wrasse, Hosik Kam, Yong Ha Kim, and Nelson Jorge Schuch. "Gravity Wave Investigations over Comandante Ferraz Antarctic Station in 2017: General Characteristics, Wind Filtering and Case Study." Atmosphere 11, no. 8 (August 18, 2020): 880. http://dx.doi.org/10.3390/atmos11080880.
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This work presents the characteristics of gravity waves observed over Comandante Ferraz Antarctic Station (EACF: 62.1° S, 58.4° W). A total of 122 gravity waves were observed in 34 nights from March to October 2017, and their parameters were obtained by using the Fourier Transform spectral analysis. The majority of the observed waves presented horizontal wavelength ranging from 15 to 35 km, period from 5 to 20 min, and horizontal phase speed from 10 to 70 ± 2 m·s−1. The propagation direction showed an anisotropic condition, with the slower wave propagating mainly to the west, northwest and southeast directions, while the faster waves propagate to the east, southeast and south. Blocking diagrams for the period of April–July showed a good agreement between the wave propagation direction and the blocking positions, which are eastward oriented while the waves propagate mainly westward. A case study to investigate wave sources was conducted for the night of 20–21 July, wherein eight small-scale and one medium-scale gravity waves were identified. Reverse ray tracing model was used to investigate the gravity wave source, and the results showed that six among eight small-scale gravity waves were generated in the mesosphere. On the other hand, only two small-scale waves and the medium-scale gravity wave had likely tropospheric or stratospheric origin, however, they could not be associated with any reliable source.
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Dong, Li, and Stephen J. Colucci. "Interpreting the Opposition between Two Block-Onset Forcing Mechanisms." Journal of the Atmospheric Sciences 64, no. 6 (June 2007): 2091–104. http://dx.doi.org/10.1175/jas3936.1.
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The opposition between two block-onset forcing mechanisms, previously identified in midtropospheric analyses over the Southern Hemisphere midlatitudes, is analytically interpreted with an idealized model. These mechanisms are the interaction (Finter) between deformation and potential vorticity and the advection (Fadv) of meridionally varying potential vorticity. Weather systems of concern, primarily consisting of planetary- and synoptic-scale waves, mostly fall into two regimes of zonal and meridional wavenumber space in which the opposition between the two block-onset forcing mechanisms is analytically derived. A synoptic interpretation of this opposition is schematically presented within the framework of barotropic dynamics. It is found that whether blocking occurs in diffluent or confluent flow depends upon the critical wavelength associated with the geostrophic flow. Blocking tends to take place in the diffluent flow of long waves in which Finter dominates over Fadv. In addition, blocking also tends to occur in the confluent flow of relative short waves in which Fadv prevails over Finter. An investigation of Rossby wave phase speeds in one diagnosed case reveals a lengthening with time of the dominant wave until it reaches the stationary wavelength on the block-onset day. In this context blocking may be understood as a stationarity and thus persistence of one of the two block-onset forcing mechanisms.
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Takaya, Koutarou, and Hisashi Nakamura. "Mechanisms of Intraseasonal Amplification of the Cold Siberian High." Journal of the Atmospheric Sciences 62, no. 12 (December 1, 2005): 4423–40. http://dx.doi.org/10.1175/jas3629.1.
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Abstract Mechanisms of intraseasonal amplification of the Siberian high are investigated on the basis of composite anomaly evolution for its strongest events at each of the grid points over Siberia. At each location, the amplification of the surface high is associated with formation of a blocking ridge in the upper troposphere. Over central and western Siberia, what may be called “wave-train (Atlantic-origin)” type is common, where a blocking ridge forms as a component of a quasi-stationary Rossby wave train propagating across the Eurasian continent. A cold air outbreak follows once anomalous surface cold air reaches the northeastern slope of the Tibetan Plateau. It is found through the potential vorticity (PV) inversion technique that interaction between the upper-level stationary Rossby wave train and preexisting surface cold anomalies is essential for the strong amplification of the surface high. Upper-level PV anomalies associated with the wave train reinforce the cold anticyclonic anomalies at the surface by inducing anomalous cold advection that counteracts the tendency of the thermal anomalies themselves to migrate eastward as surface thermal Rossby waves. The surface cold anomalies thus intensified, in turn, act to induce anomalous vorticity advection aloft that reinforces the blocking ridge and cyclonic anomalies downstream of it that constitute the propagating wave train. The baroclinic development of the anomalies through this vertical coupling is manifested as a significant upward flux of wave activity emanating from the surface cold anomalies, which may be interpreted as dissipative destabilization of the incoming external Rossby waves.
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Rodrigues, Regina R., and Tim Woollings. "Impact of Atmospheric Blocking on South America in Austral Summer." Journal of Climate 30, no. 5 (February 20, 2017): 1821–37. http://dx.doi.org/10.1175/jcli-d-16-0493.1.
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Abstract This study investigates atmospheric blocking over eastern South America in austral summer for the period of 1979–2014. The results show that blocking over this area is a consequence of propagating Rossby waves that grow to large amplitudes and eventually break anticyclonically over subtropical South America (SSA). The SSA blocking can prevent the establishment of the South Atlantic convergence zone (SACZ). As such, years with more blocking days coincide with years with fewer SACZ days and reduced precipitation. Convection mainly over the Indian Ocean associated with Madden–Julian oscillation (MJO) phases 1 and 2 can trigger the wave train that leads to SSA blocking whereas convection over the western/central Pacific associated with phases 6 and 7 is more likely to lead to SACZ events. It is found that the MJO is a key source of long-term variability in SSA blocking frequency. The wave packets associated with SSA blocking and SACZ episodes differ not only in their origin but also in their phase and refraction pattern. The tropopause-based methodology used here is proven to reliably identify events that lead to extremes of surface temperature and precipitation over SSA. Up to 80% of warm surface air temperature extremes occur simultaneously with SSA blocking events. The frequency of SSA blocking days is highly anticorrelated with the rainfall over southeast Brazil. The worst droughts in this area, during the summers of 1984, 2001, and 2014, are linked to record high numbers of SSA blocking days. The persistence of these events is also important in generating the extreme impacts.
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Nakamura, Noboru, and Clare S. Y. Huang. "Local Wave Activity and the Onset of Blocking along a Potential Vorticity Front." Journal of the Atmospheric Sciences 74, no. 7 (July 1, 2017): 2341–62. http://dx.doi.org/10.1175/jas-d-17-0029.1.
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Abstract Interaction between a train of transient waves and a diffluent westerly jet is examined using a regional quasigeostrophic equivalent barotropic model with a (nearly) binary potential vorticity (PV) distribution. Unlike most previous studies, but consistent with the observed extratropical tropopause, cross-stream variation in the layer thickness is allowed to contribute to the discontinuity in PV. In all cases examined, short (i.e., barotropic) edge waves are continuously forced in the upstream, then migrate downstream, and eventually exit the domain. A quasilinear 1D theory based on the conservation of local wave activity predicts that no steady wave train can be maintained where the westerly zonal flow is decelerated below one-half of the initial value, at which point the wave envelope develops a migratory shock analogous to the Lighthill–Whitham–Richards traffic flow problem. Fully nonlinear high-resolution 2D calculations show that the wave train indeed undergoes a significant transformation once the zonal flow along the jet axis is decelerated below the threshold. The subsequent flow evolution depends on the nature of the discontinuity in the basic-state PV. When the discontinuity is entirely due to the vorticity profile, waves are compressed and partially deflected sideways but no complete blocking occurs. When the discontinuity in PV is augmented by the layer thickness variation, the incident wave train is blocked and split into two tracks at the stagnation point, eventually leading to a formation of a modon-like vortex pair, reminiscent of an atmospheric blocking. Implications for low-frequency variability of the atmosphere are discussed.
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Das, Santu, Prakash Kar, Trilochan Sahoo, and Michael H. Meylan. "Flexural-gravity wave motion in the presence of shear current: Wave blocking and negative energy waves." Physics of Fluids 30, no. 10 (October 2018): 106606. http://dx.doi.org/10.1063/1.5052228.
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Shugan, I. V., H. H. Hwung, and R. Y. Yang. "Benjamin–Feir instability of waves in the presence of current." Nonlinear Processes in Geophysics Discussions 1, no. 2 (December 5, 2014): 1803–32. http://dx.doi.org/10.5194/npgd-1-1803-2014.
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Abstract. The development of Benjamin–Feir instability of Stokes waves in the presence of variable current is presented. We employ a model of a resonance system having three coexisting nonlinear waves and nonuniform current. The model is free from the narrow-band approximation for surface waves and relatively weak adverse current. The modulation instability of Stokes waves in nonuniform moving media has special properties. Interaction with countercurrent accelerates the growth of sideband modes on a short spatial scale. An increase in initial wave steepness intensifies the wave energy exchange accompanied by wave breaking dissipation, results in asymmetry of sideband modes and a frequency downshift with an energy transfer jump to the lower sideband mode, and depresses the higher sideband and carrier wave. Nonlinear waves may even overpass the blocking barrier produced by strong adverse current. The frequency downshift of the energy peak is permanent and the system does not revert to its initial state. We find reasonable correspondence between the results of model simulations and available experimental results for wave interaction with blocking opposing current. Large transient or freak waves with amplitude and steepness several times those of normal waves may form during temporal nonlinear focusing of the resonant waves accompanied by energy income from sufficiently strong opposing current. We employ the resonance model for the estimation of the maximum amplification of wave amplitudes as a function of gradually increasing opposing current and compare the result obtained with recently published experimental results and modeling results obtained with the nonlinear Schrödinger equation.
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Huang, Jinlong, Wenshou Tian, Lesley J. Gray, Jiankai Zhang, Yan Li, Jiali Luo, and Hongying Tian. "Preconditioning of Arctic Stratospheric Polar Vortex Shift Events." Journal of Climate 31, no. 14 (June 13, 2018): 5417–36. http://dx.doi.org/10.1175/jcli-d-17-0695.1.
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Abstract This study examines the preconditioning of events in which the Arctic stratospheric polar vortex shifts toward Eurasia (EUR events), North America (NA events), and the Atlantic (ATL events) using composite analysis. An increase in blocking days over northern Europe and a decrease in blocking days over the Bering Strait favor the movement of the vortex toward Eurasia, while the opposite changes in blocking days over those regions favor the movement of the vortex toward North America. An increase in blocking days over the eastern North Atlantic and a decrease in blocking days over the Bering Strait are conducive to movement of the stratospheric polar vortex toward the Atlantic. These anomalous precursor blocking patterns are interpreted in terms of the anomalous zonal wave-1 or wave-2 planetary wave fluxes into the stratosphere that are known to influence the vortex position and strength. In addition, the polar vortex shift events are further classified into events with small and large polar vortex deformation, since the two types of events are likely to have a different impact at the surface. A significant difference in the zonal wave-2 heat flux into the lower stratosphere exists prior to the two types of events and this is linked to anomalous blocking patterns. This study further defines three types of tropospheric blocking events in which the spatial patterns of blocking frequency anomalies are similar to the blocking patterns prior to EUR, NA, and ATL events, respectively, and our reanalysis reveals that the polar vortex is indeed more likely to shift toward Eurasia, North America, and the Atlantic in the presence of the above three defined tropospheric blocking events. These shifts of the polar vortex toward Eurasia, North America, and the Atlantic lead to statistically significant negative height anomalies near the tropopause and corresponding surface cooling anomalies over these three regions.
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Ikeda, H., and M. Mimura. "Wave-Blocking Phenomena in Bistable Reaction-Diffusion Systems." SIAM Journal on Applied Mathematics 49, no. 2 (April 1989): 515–38. http://dx.doi.org/10.1137/0149030.
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陈, 悦. "f Plane-Atmosphere Blocking the Rossby Solitary Wave." Advances in Applied Mathematics 06, no. 03 (2017): 388–97. http://dx.doi.org/10.12677/aam.2017.63045.
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Huang, Clare S. Y., and Noboru Nakamura. "Local Finite-Amplitude Wave Activity as a Diagnostic of Anomalous Weather Events." Journal of the Atmospheric Sciences 73, no. 1 (December 21, 2015): 211–29. http://dx.doi.org/10.1175/jas-d-15-0194.1.
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Abstract Finite-amplitude Rossby wave activity (FAWA) proposed by Nakamura and Zhu measures the waviness of quasigeostrophic potential vorticity (PV) contours and the associated modification of the zonal-mean zonal circulation, but it does not distinguish longitudinally localized weather anomalies, such as atmospheric blocking. In this article, FAWA is generalized to local wave activity (LWA) to diagnose eddy–mean flow interaction on the regional scale. LWA quantifies longitude-by-longitude contributions to FAWA following the meridional displacement of PV from the circle of equivalent latitude. The zonal average of LWA recovers FAWA. The budget of LWA is governed by the zonal advection of LWA and the radiation stress of Rossby waves. The utility of the diagnostic is tested with a barotropic vorticity equation on a sphere and meteorological reanalysis data. Compared with the previously derived Eulerian impulse-Casimir wave activity, LWA tends to be less filamentary and emphasizes large isolated vortices involving reversals of meridional gradient of potential vorticity. A pronounced Northern Hemisphere blocking episode in late October 2012 is well captured by a high-amplitude, near-stationary LWA. These analyses reveal that the nonacceleration relation holds approximately over regional scales: the growth of phase-averaged LWA and the deceleration of local zonal wind are highly correlated. However, marked departure from the exact nonacceleration relation is also observed during the analyzed blocking event, suggesting that the contributions from nonadiabatic processes to the blocking development are significant.
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Davini, Paolo, Chiara Cagnazzo, Silvio Gualdi, and Antonio Navarra. "Bidimensional Diagnostics, Variability, and Trends of Northern Hemisphere Blocking." Journal of Climate 25, no. 19 (April 5, 2012): 6496–509. http://dx.doi.org/10.1175/jcli-d-12-00032.1.
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Abstract In this paper, Northern Hemisphere winter blocking is analyzed through the introduction of a set of new bidimensional diagnostics based on geopotential height that provide information about the occurrence, the duration, the intensity, and the wave breaking associated with the blocking. This analysis is performed with different reanalysis datasets in order to evaluate the sensitivity of the index and the diagnostics adopted. In this way, the authors are able to define a new category of blocking placed at low latitudes that is similar to midlatitude blocking in terms of the introduced diagnostics but is unable to divert or block the flow. Furthermore, over the Euro-Atlantic sector it is shown that it is possible to phenomenologically distinguish between high-latitude blocking occurring over Greenland, north of the jet stream and dominated by cyclonic wave breaking, and the traditional midlatitude blocking localized over Europe and driven by anticyclonic wave breaking. These latter events are uniformly present in a band ranging from the Azores up to Scandinavia. Interestingly, a similar distinction cannot be pointed out over the Pacific basin where the blocking activity is dominated by high-latitude blocking occurring over eastern Siberia. Finally, considering the large impact that blocking may have on the Northern Hemisphere, an analysis of the variability and the trend is carried out. This shows a significant increase of Atlantic low-latitude blocking frequency and an eastward displacement of the strongest blocking events over both the Atlantic and Pacific Oceans.
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Masato, Giacomo, Brian J. Hoskins, and Tim Woollings. "Wave-Breaking Characteristics of Northern Hemisphere Winter Blocking: A Two-Dimensional Approach." Journal of Climate 26, no. 13 (July 1, 2013): 4535–49. http://dx.doi.org/10.1175/jcli-d-12-00240.1.
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Abstract This paper generalizes and applies recently developed blocking diagnostics in a two-dimensional (2D) latitude–longitude context, which takes into consideration both mid- and high-latitude blocking. These diagnostics identify characteristics of the associated wave breaking as seen in the potential temperature θ on the dynamical tropopause, particularly the cyclonic or anticyclonic direction of wave breaking (“DB index”) and the relative intensity (“RI index”) of the air masses that contribute to blocking formation. The methodology is extended to a 2D domain and a cluster technique is deployed to classify mid- and high-latitude blocking according to the wave-breaking characteristics. Midlatitude blocking is observed over Europe and Asia, where the meridional gradient of θ is generally weak, whereas high-latitude blocking is mainly present over the oceans, to the north of the jet stream, where the meridional gradient of θ is much stronger. They occur on the equatorward and poleward flank of the jet stream, respectively, where the horizontal shear ∂u/∂y is positive in the first case and negative in the second case. A regional analysis is also conducted. Warm-cyclonic blocking over the Pacific and cold-anticyclonic blocking over Europe are identified as the most persistent types and are associated with large amplitude anomalies in temperature and precipitation. Finally, the high-latitude cyclonic events seem to correlate well with low-frequency modes of variability over the Pacific and Atlantic Oceans.
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Menchaca, Maximo Q., and Dale R. Durran. "The Impact of Mountain Waves on an Idealized Baroclinically Unstable Large-Scale Flow." Journal of the Atmospheric Sciences 75, no. 9 (August 30, 2018): 3285–302. http://dx.doi.org/10.1175/jas-d-17-0396.1.
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Abstract The feedback of mountain waves and low-level blocking on an idealized baroclinically unstable wave passing over an isolated ridge is examined through numerical simulation. Theoretical analysis implies that the volume-integrated perturbation momentum budget is dominated by mean-flow deceleration, the divergence of vertical fluxes of horizontal momentum, and the Coriolis force acting on the perturbation ageostrophic wind. These do indeed appear as the dominant balances in numerically computed budgets averaged over layers containing 1) wave breaking in the lower stratosphere, 2) flow blocking with wave breaking near the surface, and 3) a region of pronounced horizontally averaged mean-flow deceleration in the upper troposphere where there is no wave breaking. The local impact of wave breaking on the jet in the lower stratosphere is dramatic, with winds in the jet core reduced by almost 50% relative to the no-mountain case. Although it is the layer with the strongest average deceleration, the local patches of decelerated flow are weakest in the upper troposphere. The cross-mountain pressure drag over a 2-km-high ridge greatly exceeds the vertical momentum flux at mountain-top level because of low-level wave breaking, blocking, and lateral flow diversion. These pressure drags and the low-level momentum fluxes are significantly different from corresponding values computed for simulations with steady forcing matching the instantaneous conditions over the mountain in the evolving large-scale flow.
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Das, S., T. Sahoo, and M. H. Meylan. "Dynamics of flexural gravity waves: from sea ice to Hawking radiation and analogue gravity." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 474, no. 2209 (January 2018): 20170223. http://dx.doi.org/10.1098/rspa.2017.0223.
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The propagation of flexural gravity waves, routinely used to model wave interaction with sea ice, is studied, including the effect of compression and current. A number of significant and surprising properties are shown to exist. The occurrence of blocking above a critical value of compression is illustrated. This is analogous to propagation of surface gravity waves in the presence of opposing current and light wave propagation in the curved space–time near a black hole, therefore providing a novel system for studying analogue gravity. Between the blocking and buckling limit of the compressive force, the dispersion relation possesses three positive real roots, contrary to an earlier observation of having a single positive real root. Negative energy waves, in which the phase and group velocity point in opposite directions, are also shown to exist. In the presence of an opposing current and certain critical ranges of compressive force, the second blocking point shifts from the positive to the negative branch of the dispersion relation. Such a shift is known as the Hawking effect from the analogous behaviour in the theory of relativity which leads to Hawking radiation. The theory we develop is illustrated with simulations of linear waves in the time domain.
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MA, Y., G. DONG, M. PERLIN, X. MA, G. WANG, and J. XU. "Laboratory observations of wave evolution, modulation and blocking due to spatially varying opposing currents." Journal of Fluid Mechanics 661 (August 19, 2010): 108–29. http://dx.doi.org/10.1017/s0022112010002880.
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The nonlinear evolution of waves propagating on a spatially varying opposing current has been observed in a wave–current flume. Regular waves with different initial periods and different initial steepness, s (0.05 < s < 0.19), were generated and observed. Frequency downshift, even with very small initial steepness, was identified. As expected, it was found that opposing currents can have significant interactions with wavetrains. The ultimate frequency downshift increases with the increase in initial steepness. The evolution of frequency modulation was observed via the instantaneous frequency extracted by the Morlet-wavelet transform. The instantaneous frequency showed that often the process of frequency downshift can be local in time and gradual, but abrupt changes of local frequency were also detected. The presence of an opposing current can gradually block the primary wave energy and destroy the conservation of the wave action at downwave locations, thus increasing the asymmetric modulation and accelerating the effective frequency downshift.
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Spensberger, Clemens, and Thomas Spengler. "A New Look at Deformation as a Diagnostic for Large-Scale Flow." Journal of the Atmospheric Sciences 71, no. 11 (October 29, 2014): 4221–34. http://dx.doi.org/10.1175/jas-d-14-0108.1.
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Abstract Deformation plays a key role in atmospheric dynamics because it provides a dynamical measure of the interaction between different scales, such as in frontogenesis. A climatology of deformation constructed from Interim ECMWF Re-Analysis (ERA-Interim) data (1979–2013) reveals four main processes associated with deformation: 1) frontogenesis at lower levels, 2) movement and evolution of jet streams in the upper troposphere, 3) orographic blocking, and 4) Rossby wave breaking. The merits of deformation as an additional perspective are discussed for these processes on the basis of case studies and composite analyses in conjunction with analytic solutions. This study shows that deformation can be used to unambiguously detect orographic blocking through the local strength of the flow diversion around orography. Moreover, the deformation signature for orographic blocking observed in case studies and composites closely resembles the analytic solution for two-dimensional flow around an obstacle. The climatology also reveals that Rossby wave breaking is associated with a characteristic γ-shaped deformation maximum. A composite analysis of this process confirms previous findings that suggested a dynamic link between Rossby wave breaking and dynamic blocking. It is shown that the deformation associated with Rossby wave breaking is aligned with the observed mean deformation upstream and downstream of a blocking high. Therefore, the presented composites illustrate a potential mechanism pinpointing how Rossby wave breaking can act to reinforce the flow diversion around the block.
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Tyrlis, E., and B. J. Hoskins. "The Morphology of Northern Hemisphere Blocking." Journal of the Atmospheric Sciences 65, no. 5 (May 1, 2008): 1653–65. http://dx.doi.org/10.1175/2007jas2338.1.
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Abstract The morphology of regional blocking in the Northern Hemisphere is discussed using the 40-yr ECMWF Re-Analysis (ERA-40) dataset and a measure of blocking based on the reversal at storm-track latitudes of meridional θ contrasts on a potential vorticity (PV) surface representative of the tropopause. The focus is on cyclonic and anticyclonic Rossby wave breaking that is inherent to the blocking development, and the extent to which this is determined by the climatological jet position and the ambient shears. More generally, the importance of the climatological planetary scale is discussed. The approach is mainly through composite behavior, but informed by consideration of many individual events. A diversity of behavior is found with longitude in both winter and summer, and there is a striking reversal of the sense of the wave breaking between the two seasons that is generally consistent with the difference in the jet locations. Preferred behaviors are found in various regions and seasons, and retrogression of blocking is discussed.
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Zhou, Zhen-Wei, Xi-Guang Wang, Yao-Ghuang Nie, Qing-Lin Xia, and Guang-Hua Guo. "Strong high-frequency spin waves released periodically from a confined region." European Physical Journal Applied Physics 91, no. 3 (September 2020): 30601. http://dx.doi.org/10.1051/epjap/2020200144.
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Efficient excitation of spin waves is a key issue in magnonics. Here, by using micromagnetic simulation and analytical analysis, we study the excitation of spin waves confined in a limited region by a microwave field with assistance of spin-transfer torque. The results show that the spin-transfer torque can decrease the effective damping constant and increase the spin wave relaxation time substantially. As a result, the amplitude of the excited spin waves is increased greatly. By periodically lifting and establishing the blocking areas, strong spin-wave pulses are released from the confined region. Such generated spin-wave pulses are much stronger than traditionally excited spin waves, especially for high-frequency spin waves. Our study provides a new method to generate strong high-frequency spin waves.
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Hwang, Jaeyoung, Patrick Martineau, Seok-Woo Son, Takafumi Miyasaka, and Hisashi Nakamura. "The Role of Transient Eddies in North Pacific Blocking Formation and Its Seasonality." Journal of the Atmospheric Sciences 77, no. 7 (July 1, 2020): 2453–70. http://dx.doi.org/10.1175/jas-d-20-0011.1.
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AbstractThe mechanism of North Pacific (NP) blocking formation is investigated by conducting a reanalysis-based budget analysis of the quasigeostrophic geopotential tendency equation. It is confirmed that the amplification of NP blocking anomalies primarily results from vorticity fluxes with a minor contribution of heat fluxes. In winter, the cross-frequency vorticity fluxes, resulting from interactions between high-frequency eddies and the slowly varying background flow, dominate the blocking formation. The cross-frequency vorticity fluxes, however, become substantially weaker and comparable to the low-frequency vorticity fluxes in summer. This seasonality indicates that the mechanism of NP blocking formation varies with seasons due to the different background flow. It is further found that NP blocking formation is not sensitive to the region of formation (i.e., western vs eastern NP) nor to the type of wave breaking (i.e., cyclonic vs anticyclonic wave breaking).
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Renwick, James A., and Michael J. Revell. "Blocking over the South Pacific and Rossby Wave Propagation." Monthly Weather Review 127, no. 10 (October 1999): 2233–47. http://dx.doi.org/10.1175/1520-0493(1999)127<2233:botspa>2.0.co;2.
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HANSEN, ANTHONY R., and ALFONSO SUTERA. "A comparison between planetary-wave flow regimes and blocking." Tellus A 45, no. 4 (August 1993): 281–88. http://dx.doi.org/10.1034/j.1600-0870.1993.t01-3-00003.x.
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Hansen, Anthony R., and Alfonso Sutera. "A comparison between planetary-wave flow regimes and blocking." Tellus A: Dynamic Meteorology and Oceanography 45, no. 4 (January 1993): 281–88. http://dx.doi.org/10.3402/tellusa.v45i4.14892.
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Glushkov, E. V., N. V. Glushkova, and E. M. Shapar. "Blocking of a Rayleigh wave by a subsurface crack." Doklady Physics 49, no. 10 (October 2004): 608–13. http://dx.doi.org/10.1134/1.1815424.
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Dehai, Luo, and Ji Liren. "Algebraic rossby solitary wave and blocking in the atmosphere." Advances in Atmospheric Sciences 5, no. 4 (December 1988): 445–54. http://dx.doi.org/10.1007/bf02656790.
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