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Wen Chen - One of the best experts on this subject based on the ideXlab platform.
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dynamics of 2013 sudden stratospheric warming event and its impact on cold weather over eurasia role of Planetary Wave reflection
Scientific Reports, 2016Co-Authors: Debashis Nath, Cai Zelin, Wen Chen, A. I. PogoreltsevAbstract:In the present study, we investigate the impact of stratospheric Planetary Wave reflection on tropospheric weather over Central Eurasia during the 2013 Sudden Stratospheric Warming (SSW) event. We analyze EP fluxes and Plumb Wave activity fluxes to study the two and three dimensional aspects of Wave propagation, respectively. The 2013 SSW event is excited by the combined influence of Wavenumber 1 (WN1) and Wavenumber 2 (WN2) Planetary Waves, which makes the event an unusual one and seems to have significant impact on tropospheric weather regime. We observe an extraordinary development of a ridge over the Siberian Tundra and the North Pacific during first development stage (last week of December 2012) and later from the North Atlantic in the second development stage (first week of January 2013), and these Waves appear to be responsible for the excitation of the WN2 pattern during the SSW. The Wave packets propagated upward and were then reflected back down to central Eurasia due to strong negative wind shear in the upper stratospheric polar jet, caused by the SSW event. Waves that propagated downward led to the formation of a deep trough over Eurasia and brought extreme cold weather over Kazakhstan, the Southern part of Russia and the Northwestern part of China during mid-January 2013.
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impact of Planetary Wave reflection on tropospheric blocking over the urals siberia region in january 2008
Advances in Atmospheric Sciences, 2016Co-Authors: Debashis Nath, Wen ChenAbstract:Planetary Wave reflection from the stratosphere played a significant role in changing the tropospheric circulation pattern over Eurasia in mid-January 2008. We studied the 2008 event and compared with composite analysis (winters of 2002/2003, 2004/2005, 2006/2007, 2007/2008, 2010/2011 and 2011/2012), when the downward coupling was stronger, by employing time-lagged singular value decomposition analysis on the geopotential height field. In the Northern Hemisphere, the geopotential fields were decomposed into zonal mean and Wave components to compare the relative covariance patterns. It was found that the Wavenumber 1 (WN1) component was dominant compared with the Wavenumber 2 (WN2) component and zonal mean process. For the WN1 field, the covariance was much higher (lower) for the negative (positive) lag, with a prominent peak around +15 days when the leading stratosphere coupled strongly with the troposphere. It contributed to the downward coupling due to reflection, when the stratosphere exhibited a partially reflective background state. We also analyzed the evolution of the WN1 anomaly and heat flux anomaly, both in the troposphere and stratosphere, during January–March 2008. The amplitude of the tropospheric WN1 pattern reached a maximum and was consistent with a downward Wave coupling event influenced by the stratospheric WN1 anomaly at 10 hPa. This was consistent with the reflection of the WN1 component over Eurasia, which triggered an anomalous blocking high in the Urals–Siberia region. We further clarified the impact of reflection on the tropospheric WN1 field and hence the tropospheric circulation pattern by changing the propagation direction during and after the event.
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Planetary Wave reflection and its impact on tropospheric cold weather over asia during january 2008
Advances in Atmospheric Sciences, 2014Co-Authors: Debashis Nath, Wen Chen, Lin WangAbstract:Reflection of stratospheric Planetary Waves and its impact on tropospheric cold weather over Asia during January 2008 were investigated by applying two dimensional Eliassen-Palm (EP) flux and three-dimensional Plumb Wave activity fluxes. The Planetary Wave propagation can clearly be seen in the longitude-height and latitude-height sections of the Plumb Wave activity flux and EP flux, respectively, when the stratospheric basic state is partially reflective. Primarily, a Wave packet emanating from Baffin Island/coast of Labrador propagated eastward, equatorward and was reflected over Central Eurasia and parts of China, which in turn triggered the advection of cold wind from the northern part of the boreal forest regions and Siberia to the subtropics. The wide region of Central Eurasia and China experienced extreme cold weather during the second ten days of January 2008, whereas the extraordinary persistence of the event might have occurred due to an anomalous blocking high in the Urals-Siberia region.
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interdecadal variations of the east asian winter monsoon and their association with quasi stationary Planetary Wave activity
Journal of Climate, 2009Co-Authors: Lin Wang, Wen Chen, Ronghui Huang, Lihua KangAbstract:Abstract Interdecadal variations of the East Asian winter monsoon (EAWM) and their association with the quasi-stationary Planetary Wave activity are analyzed by using the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis dataset and the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis dataset. It is found that the EAWM experienced a significant weakening around the late 1980s; that is, the EAWM was strong during 1976–87 and became weak after 1988. This leads to an obvious increase in the wintertime surface air temperature as well as a decrease in the frequency of occurrence of cold Waves over East Asia. The dynamical process through which the EAWM is weakened is investigated from the perspective of quasi-stationary Planetary Waves. It is found that both the propagation and amplitude of quasi-stationary Planetary Waves have experienced obvious interdecadal variations, which are well related to those of the EAWM. Compared to the period 1976...
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Modulation of northern hemisphere wintertime stationary Planetary Wave activity: East Asian climate relationships by the Quasi‐Biennial Oscillation
Journal of Geophysical Research, 2007Co-Authors: Wen Chen, Tim LiAbstract:[1] The modulation of the relationship between the tropospheric stationary Planetary Wave activity and the East Asian winter climate by the tropical quasi-biennial oscillation (QBO) wind in the stratosphere is investigated. In the QBO easterly phase, a significant warming appears in northeastern Asia in the presence of high Wave activities. This corresponds to a weakened East Asian trough at 500-hPa, which determines the extent to which cold Waves penetrate into East Asia. However, in the QBO westerly phase, both the surface warming and the weakening of the East Asian trough become insignificant in response to high Wave activities. The possible mechanism for this QBO modulation on the tropospheric Wave activities may be attributed to the indirect influence of the QBO induced polar and extratropical stratospheric circulation changes. Under the QBO easterly phase conditions, the tropospheric Wave activity flux divergence in the higher-latitude region is enhanced due to enhanced upward Eliassen-Palm (EP) flux into the stratosphere, while the Wave flux convergence in the subtropical troposphere is increased due to the decrease in the equatorward flux. This leads to an enhanced Wave activity difference and thus the associated East Asian climate anomalies become larger and robust. An opposite effect (i.e., reduced Wave activity difference) appears in the QBO westerly phase. Further analyses reveal that the QBO significantly modulates both the zonal Wave number 1 and 2 in the sea level pressure field but not for Wave number 3. The combination of Wave number 1 and 2 patterns leads to the strongest surface temperature anomalies in northern Asia.
J M Forbes - One of the best experts on this subject based on the ideXlab platform.
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Planetary Wave variability of sq currents
Journal of Geophysical Research, 2016Co-Authors: R Elhawary, J M ForbesAbstract:The E-region wind dynamo is a key linkage in atmosphere-ionosphere coupling, but relatively little is known about variability of the corresponding E-region currents in terms of connections with atmosphere dynamics. In this paper we analyze ground magnetic variations ΔB during 2009 at two mid-latitude stations to reveal Planetary-Wave (PW) periodicities near those of well-known atmospheric normal modes, i.e., 5, 10 and 16 days. In the neutral atmosphere these Waves are westward-propagating with zonal Wavenumber s = 1. The two stations are at the same magnetic latitude and are nearly conjugate in longitude, which leads to following new insights: First, the amplitude and phase variations between the two stations do not conform to simple westward-propagating Waves with zonal Wavenumber s = 1, implying that the underlying physics is more complex, in part due to modulation by the predominantly s= 1 longitude-dependent magnetic field. There is also compelling evidence that much ΔB variability near PW periods arises through the product of solar-controlled conductivity and PW-related electric field in the expression for electric current, mainly arising from solar radiation periodicities longer than the solar rotation period. For instance, interactions between solar periodicities in conductivity near 53d and 83d and PW periodicities in total electric field yield secondary peaks in the ΔB spectrum that contribute to its variability at periods less than 20d. In fact, most of the observed ΔB variability arises from these two latter sources, rather than directly from the original driving PW oscillations.
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a new interpretation of mars aerobraking variability Planetary Wave tide interactions
Journal of Geophysical Research, 2010Co-Authors: Y. Moudden, J M ForbesAbstract:[1] This study presents a new interpretation of Mars aerobraking density observations in terms of Planetary Wave-tide interactions. Mars Global Surveyor and Mars Reconnaissance Orbiter provide invaluable information about tidal activity in the lower thermosphere of Mars through the longitude structure that they reveal in near-Sun-synchronous frame of reference. However, this same perspective does not permit one to uncover the origins of day-to-day variability of these structures. Herein, by employing a new arrangement of the data and understanding the relationship between spectral features in longitude space versus UT space, we are able to attribute a significant amount of density variability in the aerobraking region to the effect of tidal modulation by Planetary Waves in the 5–20 day period range.
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modulation of the equatorial f region by the quasi 16 day Planetary Wave
Geophysical Research Letters, 2009Co-Authors: N M Pedatella, J M ForbesAbstract:[1] In situ electron density measurements from the CHAMP satellite and global positioning system total electron content (TEC) observations are used to illustrate how quasi-16-day Planetary Wave activity influences the structure of the low-latitude ionosphere. SABER temperature measurements reveal that quasi-16-day oscillations in the dynamo region (110 km) during the time interval of 1 December 2005 to 1 March 2006 are most dominant in the zonal mean. Enhancements in equatorial zonal mean temperatures in the E-region are connected with enhancements at ±10–20° magnetic latitude in zonal mean CHAMP electron densities and TEC. At a near-constant altitude of 350 km, the oscillations in daytime electron densities are greater than 40 percent of background levels. A local time effect is also observed in the Planetary Wave influence on the F-region electron densities. These results demonstrate that vertically propagating Planetary Waves induce significant variability in the low-latitude F-region ionosphere and that these effects are seen at all longitudes.
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Planetary Waves observed by timed saber in coupling the stratosphere mesosphere lower thermosphere during the winter of 2003 2004 part 2 altitude and latitude Planetary Wave structure
Journal of Atmospheric and Solar-Terrestrial Physics, 2009Co-Authors: Plamen Mukhtarov, B. Andonov, D Pancheva, N J Mitchell, J M ForbesAbstract:Abstract Part 2 of the present paper is focused on the Planetary Wave coupling from the stratosphere to the lower thermosphere (30–120 km) during the Arctic winter of 2003/2004. The Planetary Waves seen in the TIMED/SABER temperature data in the latitudinal range 50°N–50°S are studied in detail. The altitude and latitude structures of the Planetary Wave (stationary and travelling) clearly indicate that the stratosphere and mesosphere (30–90 km) are coupled by direct vertical propagation of the Planetary Waves, while the lower thermosphere (above 90–95 km altitude) is only partly connected with the lower levels probably indirectly through in-situ generation of disturbances by the dissipation and breaking of gravity Waves filtered by lower atmospheric Planetary Waves. A peculiar feature of the thermal regime in the lower thermosphere is that it is dominated by zonally symmetric Planetary Waves.
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Planetary Waves observed by TIMED/SABER in coupling the stratosphere-mesosphere-lower thermosphere during the winter of 2003/2004: Part 2-Altitude and latitude Planetary Wave structure
Journal of Atmospheric and Solar-Terrestrial Physics, 2009Co-Authors: D Pancheva, Plamen Mukhtarov, B. Andonov, N J Mitchell, J M ForbesAbstract:Abstract Part 2 of the present paper is focused on the Planetary Wave coupling from the stratosphere to the lower thermosphere (30–120 km) during the Arctic winter of 2003/2004. The Planetary Waves seen in the TIMED/SABER temperature data in the latitudinal range 50°N–50°S are studied in detail. The altitude and latitude structures of the Planetary Wave (stationary and travelling) clearly indicate that the stratosphere and mesosphere (30–90 km) are coupled by direct vertical propagation of the Planetary Waves, while the lower thermosphere (above 90–95 km altitude) is only partly connected with the lower levels probably indirectly through in-situ generation of disturbances by the dissipation and breaking of gravity Waves filtered by lower atmospheric Planetary Waves. A peculiar feature of the thermal regime in the lower thermosphere is that it is dominated by zonally symmetric Planetary Waves.
Ronghui Huang - One of the best experts on this subject based on the ideXlab platform.
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interdecadal variations of the east asian winter monsoon and their association with quasi stationary Planetary Wave activity
Journal of Climate, 2009Co-Authors: Lin Wang, Wen Chen, Ronghui Huang, Lihua KangAbstract:Abstract Interdecadal variations of the East Asian winter monsoon (EAWM) and their association with the quasi-stationary Planetary Wave activity are analyzed by using the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis dataset and the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis dataset. It is found that the EAWM experienced a significant weakening around the late 1980s; that is, the EAWM was strong during 1976–87 and became weak after 1988. This leads to an obvious increase in the wintertime surface air temperature as well as a decrease in the frequency of occurrence of cold Waves over East Asia. The dynamical process through which the EAWM is weakened is investigated from the perspective of quasi-stationary Planetary Waves. It is found that both the propagation and amplitude of quasi-stationary Planetary Waves have experienced obvious interdecadal variations, which are well related to those of the EAWM. Compared to the period 1976...
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relationship between stationary Planetary Wave activity and the east asian winter monsoon
Journal of Geophysical Research, 2005Co-Authors: Wen Chen, Song Yang, Ronghui HuangAbstract:[1] The variability of both the stationary Planetary Wave activity and the East Asian winter monsoon is strongly associated with the thermal contrast between oceans and landmasses. In this study, we explore the interannual relationship between the monsoon and the Wave activity defined by an index of the difference in the divergence of EliassenPalm flux between 50� N at 500 hPa and 40� N at 300 hPa. It is found that, compared to the winters of low Wave activity, the equatorward propagation of Planetary Waves in the middle and upper troposphere is stronger in the high Wave activity winters. During these high activity winters, the upward Wave propagation from the troposphere into the stratosphere becomes weaker. This is accompanied by a smaller perturbation in the polar vortex, which tends to be colder and stronger. In the meantime, the East Asian westerly jet stream, the East Asian trough, the Siberian high, and the Aleutian low all become weaker apparently. In particular, the weakening of the Siberian high and the Aleutian low decreases the northeasterly wind over East Asia, leading to a warming condition in the region especially in northeastern Asia. A further analysis reveals that the zonal Wavenumber-2 pattern of Planetary Waves contributes dominantly to the variability of the East Asian winter monsoon.
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The modulation of Planetary Wave propagation by the tropical QBO zonal winds and the associated effects in the residual meridional circulation
Contributions to atmospheric physics, 1999Co-Authors: Wen Chen, Ronghui HuangAbstract:The Planetary Wave-mean flow interactions during the different stage of the QBO are studied with the quasi-geostrophic zonally-averaged mean flow equations and the linearized primitive equations for Planetary Waves. In the linear case of steady flows, there is no feedback between the mean flow and the Planetary Waves. The difference of dissipating Planetary Wave propagation between easterly and westerly phases of the QBO is confined chiefly to low latitudes. The results also show that the differences of Planetary Wave amplitudes with easterly phase minus westerly phase display dipole pattern in the northern hemisphere with increasing values at high latitudes. The residual circulation indicates that there is a slightly stronger poleward and downward transport at high latitudes caused by Planetary Wave propagation during easterly than westerly phases of the QBO. In the case of coupling between the Planetary Waves and the mean flow, a noticeable difference of Planetary Wave propagation emerges clearly at middle and high latitudes with obviously larger upward and equatorward EP fluxes in the easterly phase winter than in the westerly phase winter. By modulating the propagation of Planetary Waves, the tropical QBO introduces significant variabilities of the Planetary Wave amplitudes and the residual circulation in the northern hemisphere. The amplitudes of Planetary Waves are shown to be greater during the easterly phase winter than during the westerly phase winter; the advective transport due to Planetary Waves is enhanced and the difference between these two winters becomes more evident at middle and high latitudes comparing with the linear result. The modulation of Planetary Wave propagation by the equatorial QBO winds may also explain interannual variability of ozone in the stratosphere at high latitudes. Our study provides a illustrative support for the mechanism of the QBO modulation of Planetary Wave propagation and the associated effects in the residual meridional circulation.
Judith Berner - One of the best experts on this subject based on the ideXlab platform.
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linear and nonlinear signatures in the Planetary Wave dynamics of an agcm probability density functions
Journal of the Atmospheric Sciences, 2007Co-Authors: Judith Berner, Grant BranstatorAbstract:Abstract To identify and quantify indications of linear and nonlinear Planetary Wave behavior and their impact on the distribution of atmospheric states, characteristics of a very long integration of an atmospheric general circulation model (GCM) in a four-dimensional phase space are examined. The phase space is defined by the leading four empirical orthogonal functions of 500-hPa geopotential heights. First it is established that nonlinear tendencies similar to those reported in an earlier study of the phase space behavior in this GCM have the potential to lead to non-Gaussian features in the probability density function (PDF) of Planetary Waves. Then using objective measures it is demonstrated that the model’s distribution of states has distinctive non-Gaussian features. These features are characterized in various subspaces of dimension as high as four. A key feature is the presence of three radial ridges of enhanced probability emanating from the mode, which is shifted away from the climatological mean...
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linking nonlinearity and non gaussianity of Planetary Wave behavior by the fokker planck equation
Journal of the Atmospheric Sciences, 2005Co-Authors: Judith BernerAbstract:Abstract To link prominent nonlinearities in the dynamics of 500-hPa geopotential heights to non-Gaussian features in their probability density, a nonlinear stochastic model of atmospheric Planetary Wave behavior is developed. An analysis of geopotential heights generated by extended integrations of a GCM suggests that a stochastic model and its associated Fokker–Planck equation call for a nonlinear drift and multiplicative noise. All calculations are carried out in the reduced phase space spanned by the leading EOFs. It is demonstrated that this nonlinear stochastic model of Planetary Wave behavior captures the non-Gaussian features in the probability density function of atmospheric states to a remarkable degree. Moreover, it not only predicts global temporal characteristics, but also the nonlinear, state-dependent divergence of state trajectories. In the context of this empirical modeling, it is discussed on which time scale a stochastic model is expected to approximate the behavior of a continuous dete...
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linear and nonlinear signatures in the Planetary Wave dynamics of an agcm phase space tendencies
Journal of the Atmospheric Sciences, 2005Co-Authors: Grant Branstator, Judith BernerAbstract:Abstract To identify and quantify indications of linear and nonlinear Planetary Wave behavior, characteristics of a very long integration of an atmospheric general circulation model in a four-dimensional phase space are examined. The phase space is defined by the leading four empirical orthogonal functions of 500-hPa geopotential heights, and the primary investigated characteristic is the state dependence of mean phase space tendencies. Defining the linear component of Planetary Wave tendencies as that part which can be captured by a least squares fit linear operator driven by additive Gaussian white noise, the study finds that there are distinct linear and nonlinear signatures. These signatures are especially easy to see in plots of mean tendencies projected onto phase space planes. For some planes the mean tendencies are highly linear, while for others there are strong departures from linearity. The results of the analysis are found to depend strongly on the lag time used to estimate tendencies with the...
Grant Branstator - One of the best experts on this subject based on the ideXlab platform.
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the origin of nonlinear signatures of Planetary Wave dynamics mean phase space tendencies and contributions from non gaussianity
Journal of the Atmospheric Sciences, 2007Co-Authors: Christian Franzke, Andrew J Majda, Grant BranstatorAbstract:Mean phase space tendencies are investigated to systematically identify the origin of nonlinear signatures and the dynamical significance of small deviations from Gaussianity of Planetary low-frequency Waves. A general framework for the systematic investigation of mean phase space tendencies in complex geophysical systems is derived. In the special case of purely Gaussian statistics, this theory predicts that the interactions among the Planetary Waves themselves are the source of the nonlinear signatures in phase space, whereas the unresolved Waves contribute only an amplitude-independent forcing, and cannot contribute to any nonlinear signature. The predictions of the general framework are studied for a simple stochastic climate model. This toy model has statistics that are very close to being Gaussian and a strong nonlinear signature in the form of a double swirl in the mean phase space tendencies of its low-frequency variables, much like recently identified signatures of nonlinear Planetary Wave dynamics in prototype and comprehensive atmospheric general circulation models (GCMs). As predicted by the general framework for the Gaussian case, the double swirl results from nonlinear interactions of the low-frequency variables. Mean phase space tendencies in a reduced space of a prototype atmospheric GCM are also investigated. Analysis of the dynamics producing nonlinear signatures in these mean tendencies shows a complex interplay between Waves resolved in the subspace and unresolved Waves. The interactions among the resolved Planetary Waves themselves do not produce the nonlinear signature. It is the interaction with the unresolved Waves that is responsible for the nonlinear dynamics. Comparing this result with the predictions of the general framework for the Gaussian case shows that the impact of the unresolved Waves is due to their small deviations from Gaussianity. This suggests that the observed deviations from Gaussianity, even though small, are dynamically relevant.
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linear and nonlinear signatures in the Planetary Wave dynamics of an agcm probability density functions
Journal of the Atmospheric Sciences, 2007Co-Authors: Judith Berner, Grant BranstatorAbstract:Abstract To identify and quantify indications of linear and nonlinear Planetary Wave behavior and their impact on the distribution of atmospheric states, characteristics of a very long integration of an atmospheric general circulation model (GCM) in a four-dimensional phase space are examined. The phase space is defined by the leading four empirical orthogonal functions of 500-hPa geopotential heights. First it is established that nonlinear tendencies similar to those reported in an earlier study of the phase space behavior in this GCM have the potential to lead to non-Gaussian features in the probability density function (PDF) of Planetary Waves. Then using objective measures it is demonstrated that the model’s distribution of states has distinctive non-Gaussian features. These features are characterized in various subspaces of dimension as high as four. A key feature is the presence of three radial ridges of enhanced probability emanating from the mode, which is shifted away from the climatological mean...
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linear and nonlinear signatures in the Planetary Wave dynamics of an agcm phase space tendencies
Journal of the Atmospheric Sciences, 2005Co-Authors: Grant Branstator, Judith BernerAbstract:Abstract To identify and quantify indications of linear and nonlinear Planetary Wave behavior, characteristics of a very long integration of an atmospheric general circulation model in a four-dimensional phase space are examined. The phase space is defined by the leading four empirical orthogonal functions of 500-hPa geopotential heights, and the primary investigated characteristic is the state dependence of mean phase space tendencies. Defining the linear component of Planetary Wave tendencies as that part which can be captured by a least squares fit linear operator driven by additive Gaussian white noise, the study finds that there are distinct linear and nonlinear signatures. These signatures are especially easy to see in plots of mean tendencies projected onto phase space planes. For some planes the mean tendencies are highly linear, while for others there are strong departures from linearity. The results of the analysis are found to depend strongly on the lag time used to estimate tendencies with the...