The Propagation and Transport Effect of Planetary Waves in the Northern Hemisphere Winter

Based on the transformed Eulerian-mean equations, the dynamics of planetary waves are discussed. Both observations and simulations indicate that in the Northern Hemisphere winter there are two waveguides for the meridional propagation of quasi-stationary planetary waves. One is the high latitude waveguide, and the other is the low latitude waveguide. These results are in good agreement with theoretical analysis. Moreover, the convergence of EP flux indicates that the stratospheric sudden warming is the result of anomalous planetary wave propagation along the high latitude waveguide and its interaction with mean flows. The tropical quasi-biennial oscillation (QBO) winds, which represent one significant variation of zonal flow in the lower stratosphere at low latitudes, can influence the low latitude waveguide of planetary wave propagation. Our results of the wave-mean flow coupled model show that these tropical winds can also modulate the high latitude waveguide significantly in the case of wave-mean flow interaction.The transport effect of planetary waves on ozone is also analyzed. The residual mean circulation forced by planetary waves indicates that there is strong transport circulation for the dissipative planetary waves. Under the forcing of northward eddy heat transport, a positive transport circulation can result which rises at low latitudes and sinks at high latitudes. At the same time, the modification of planetary wave propagation by the equatorial QBO winds is shown to have an important impact on the transport circulation. The model results indicate that the meridional transport is amplified during the easterly phase of the QBO. This mechanism may explain the interannual variability of ozone in the stratosphere at high latitudes.

Planetary Wave Reflection and Its Impact on Tropospheric Cold Weather over Asia during January 2008

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.

Impact of Planetary Wave Reflection on Tropospheric Blocking over the Urals–Siberia Region in January 2008

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, 200412005, 200612007, 200712008, 201012011 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 geopo- tential 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 WNI 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 WNI anomaly and heat flux anomaly, both in the troposphere and stratosphere, during January- March 2008. The amplitude of the tropospheric WN 1 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 WNI field and hence the tropospheric circulation pattern by changing the propagation direction during and after the event.

The Role of Stationary and Transient Planetary Waves in the Maintenance of Stratospheric Polar Vortex Regimes in Northern Hemisphere Winter

Using 1958-2002 NCEPNCAR reanalysis data, we investigate stationary and transient planetary wave propagation and its role in wave-mean flow interaction which influences the state of the polar vortex （PV） in the stratosphere in Northern Hemisphere （NH） winter. This is done by analyzing the Eliassen-Palm （E-P） flux and its divergence. We find that the stationary and transient waves propagate upward and equatorward in NH winter, with stronger upward propagation of stationary waves from the troposphere to the stratosphere, and stronger equatorward propagation of transient waves from mid-latitudes to the subtropics in the troposphere. Stationary waves exhibit more upward propagation in the polar stratosphere during the weak polar vortex regime （WVR） than during the strong polar vortex regime （SVR）. On the other hand, transient waves have more upward propagation during SVR than during WVR in the subpolar stratosphere, with a domain of low frequency waves. With different paths of upward propagation, both stationary and transient waves contribute to the maintenance of the observed stratospheric PV regimes in NH winter.

Inter-annual variations of 6.5-day planetary waves and their relations with QBO

This paper studies inter-annual variations of 6.5-Day Waves(6.5 DWs) observed at altitudes 20-110 km between 52°S-52°N latitudes during March 2002-January 2021, and how these variations were related to the equatorial stratospheric Quasi-Biennial Oscillation(QBO). Temperature amplitudes of the 6.5 DWs are calculated based on SABER/TIMED observations. QBO zonal winds are obtained from an ERA5 reanalysis dataset. QBO phases are derived using an Empirical Orthogonal Functions(EOF) method. Wavelet analysis of the observed 6.5 DW variations demonstrates obvious spectral maximums around 28-38 months at 32°N-52°N, and around 26-30 months at 32°S-52°S. In the Northern Hemisphere, peak periods lengthened poleward;in the Southern Hemisphere, however,they were unchanged with latitude. Residual 6.5 DWs amplitudes have been determined by removing composite amplitudes from 6.5 DWs amplitudes. Comparisons between QBO and monthly maximum residual 6.5 DWs amplitudes(AMmax) show clear correlations between the QBO and 6.5 DWs in both hemispheres, but the observed relationship is stronger in the NH. When AMmax NH, the mean QBO profile was easterly at all levels from 70 to 5 hPa;when the AMmax below 30 hPa. Linear Pearson correlation coefficients between QBO phases and AMmax 20°N-52°N in April and around 64 km at 24°S in February, and large negative values from 80 to 110 km between 20°N-50°N in August and at 96-106 km between 20°S-44°S in February. These results indicate quantitative correlations between QBO and 6.5 DWs and provide credible evidences for further studies of QBO modulations on long-term variations of 6.5 DWs.

Responses of Planetary Waves to Global Warming: Implications from CMIP3 4×CO_2 Experiments

The planetary wave response to global warm ing with single forcing of greenhouse gases （GHGs） is investigated in this study by using a total of 11 model results that anticipated CMIP3 4XCO2 experiments. It is shown that the amplitudes of the planetary wave fluxes over Siberia, the Eastern North Pacific, and the North Atlantic decrease by approximately -10% to -30% in the warming context. In particular, the vertical wave flux over the Eastern North Pacific significantly decreases by -28.6%. The weakening of the planetary waves is partly associated with the decreased land-sea thermal contrast, which may be caused by the radiation effect of CO2 and the different surface heat capacities of land and sea. The present work provides a clear understanding of the re sponses of planetary waves to GHGs forcing.

Research on the Propagation Acting of the Equatorial Planetary Waves on the Western Equatorial Pacific Warm Pool Heat

Based on the long-term buoy data from the Tropical Atmosphere Ocean ( TAO ) —array during the TOGA ( Tropical Ocean and Global Atmosphere ) Program (19801996), the propagation acting of the Equatorial planetary waves on the Western Equatorial Pacific warm pool heat is analyzed. Results show that the zonal heat transmission in the Western Equatorial Pacific takes palace mainly in the subsurface water and spreads eastwards along the thermocline; while the seasonal westward-spreading heat change structure occurs in the mixed layers in the middle and western Pacific. The standing-form transmission in the western Pacific appears in the thermocline layer, while in the eastern pacific, it exists in the mixed layer as well as in the thermocline layer. The standing-form and eastward-spreading sign of zonal heat transmitting in the upper water is predominant and strong, and the westward sign is weak.The component force of Kelvin Equatorial wave pressure runs through the western and eastern Equatorial pacific, and transmits heat energy eastwards. And the heat transmitted by zonal current component occurs mostly in the western Pacific; The heat transmitted by the component force of Rossby wave pressure mainly appears in the eastern and middle areas of the Pacific, while the zonal current component transmitting occurs mainly in the western Pacific; Mixed-Rossby gravity wave’s action on the zonal current is stronger than that of the thermocline layer. In the mean state, the standing wave model of Equatorial Pacific up layer ocean temperature confines the transport of western Pacific warm pool heat to the eastern Pacific. Under abnormal conditions, the standing wave model of Equatorial Pacific up layer ocean temperature weakens, the eastwardly transmitting model enhances, and subsequently n^the El Ni o event occurs.

Generation of Zonal Flow and Magnetic Field by Planetary Waves in the Earth’s Ionosphere

Possibility of generation of large-scale sheared zonal flow and magnetic field by coupled under the typical ionospheric conditions short-scale planetary low-frequency waves is shown. Propagation of coupled internal-gravity-Alfven, Rossby-Khantadze, Rossby-Alfven-Khantadze and collision-less electron skin depth order drift-Alfven waves is revealed and investigated in detail. To describe the nonlinear interaction of such coupled waves with sheared zonal flow the corresponding nonlinear equations are deduced. The instability mechanism is based on the nonlinear parametric triple interaction of the finite amplitude short-scale planetary waves leading to the inverse energy cascade toward the longer wavelengths. It is shown that under such interaction intense sheared magnetic fields can be generated. Appropriate growth rates are discussed in detail.

Quasi-stationary planetary wave-mean flow interactions in the Northern Hemisphere stratosphere and their responses to ENSO events

Based on the ERA-40 reanalysis data from the European Centre for Medium-Range Weather Forecasts and the output of ECHAM5/MPI-OM, this study investigated the interactions between the quasi-stationary planetary wave （SPW） and mean flow, and their responses to E1 Nifio-Southern Oscillation （ENSO） events in the northern hemispheric stratosphere. Results show that the activity of SPW is the strongest in winter, when the SPW propagates along the polar waveguide into the stratosphere and along the low-latitude waveguide to the subtropical tropopause. The analysis of three dimensional SPW structure indicates that the main sources of SPW activity are located over the Eurasian continent and the North Pacific north of 45°N. On the one hand, the two waveguides of the SPW reflect the influence of mean flow on the propagation of the SPW. On the other hand, the upward propagating SPW can interact with the stratospheric mean flow, leading to deceleration of the zonal mean westerly. Furthermore, the SPW exhibits clear responses to ENSO events. During E1 Nifio winters, the SPW in the strat- osphere tends to propagate more upward and poleward. Its interactions with mean flow can induce a dipole pattern in zonal mean zonal winds, with accelerated westerly winds at low-middle latitudes and decelerated westerly winds at high latitudes. The ECHAM5/MPI-OM model reproduces the climatology of the SPW well. Although the simulated SPW is slightly weaker than the observations in the stratosphere, the model＇s performance has significant improvements compared with other GCMs used in previous studies. However, there are still some problems in the responses of the SPW to ENSO in the model. Although the model reproduces the responses of both the amplitude and the SPW-mean flow interactions to ENSO well in the troposphere, the stratospheric responses are quite weak. Therefore, further studies are needed to improve the simulation of the stratospheric atmospheric circulation and related dynamical processes.

INFLUENCE OF THE BASIC FLOW IN THE TROPICS ON THE STATIONARY PLANETARY WAVES AT MIDDLE AND HIGH LATITUDES DURING THE NORTHERN HEMISPHERE WINTER

The relationship between the quasi-stationary planetary waves forced by topography and heat source during the Northern Hemisphere winter is investigated by means of a quasi-geostrophic,34-level,spherical coordinate model with the Rayleigh friction,the Newtonian cooling and the horizontal eddy thermal diffu- sion. The calculated results show that when the basic flow is the westerly in the tropical stratosphere,the amplitude of quasi-stationary planetary wave for zonal wavenumber 2 at middle and high latitudes is larger during the Northern Hemispheric winter;while when the basic flow is the easterly,it is smaller.This is in agreement with the observed results. The calculated results also show that influence of the basic flow in the tropical troposphere on the quasi- stationary planetary waves is larger than that of the basic flow in the tropical stratosphere on the quasi- stationary planetary waves.

ANALYSES OF THE DYNAMIC EFFECTS ON WINTER CIRCULATION OF THE TWO MAIN MOUNTAINS IN THE NORTHERN HEMISPHERE——Ⅱ.VERTICAL PROPAGATION OF PLANETARY WAVES

A linear,hemispheric and stationary spectral model with multilayers in the vertical was employed to simulate the vertical propagation of waves triggered by mountains.Results show that,in cooperation with the East Asia zonal mean flow,Tibetan Plateau can excite a strong wavenumber 1 perturbation in the stratosphere with its ridge and trough lo- cated over the Pacific and Atlantic Oceans respectively.On the other hand,the stratospheric wavenumber 1 perturbation caused by the mechanical forcing of the Rocky Mountains in cooperation with the North America zonal mean flow is very weak.Calculations from observational data of the vertical profile of critical wavenumber for vertically propagating waves imply that the tropospheric wavenumber 1 perturbation can hardly penetrate the North America tropopause up- wards,whereas it can freely propagate through the East Asia tropopause into the stratosphere.Two-dimensional E-P cross-sections obtained from both observational data and simulated results also demonstrate that waves excited by the Rocky Mountains are refracted towards low latitudes in the troposphere during their upward propagation:whereas,in addition to the above mentioned equatorward leaning branch,the wavenumber 1 and 2 planetary waves excited by the Tibetan Plateau possess another branch which is refracted to high latitudes during upward propagation and penetrates the tropopause into the stratosphere.It is therefore concluded that the difference in the horizontal and vertical wave propagations in the two hemispheres is a result of the different dynamical forcing induced by the two main mountains in the Northern Hemisphere.

Long-term variation of Arctic Sudden Stratospheric Warmings(SSW)and potential causes

Utilizing the European Centre for Medium-Range Weather Forecast(ECMWF)Reanalysis v5(ERA5),for the first time,we have confirmed close links among Sudden Stratospheric Warmings(SSWs)in the Northern Hemisphere(NH),the polar vortices,and stratospheric Planetary Waves(PWs)by analyzing and comparing their trends.Interestingly,within overall increasing trends,the duration and strength of SSWs exhibit increasing and decreasing trends before and after the winter of 2002,respectively.To reveal possible physical mechanisms driving these trends,we analyzed the long-term trends of the winter(from December to February)polar vortices and of stratospheric PWs with zonal wave number 1.Notably,our results show that in all three time periods(the entire period of 41winters,1980 to 2020,and the two subperiods—1980-2002 and 2002-2020)enhancing SSWs were always accompanied by weakening winter polar vortices and strengthening polar PWs like Stationary Planetary Waves(SPWs)and 16-day waves,and vice versa.This is the first proof,based on ERA5 long-term trend data,that weakening polar vortices and enhancing stratospheric PWs(especially SPWs)could cause an increase in SSWs.

Northern Hemisphere Stratospheric Polar Vortex Extremes in February under the Control of Downward Wave Flux in the Lower Stratosphere

Using ECWMF ERA-40 and Interim reanalysis data, the planetary wave fluxes associated with the February extreme stratospheric polar vortex were studied. Using the three-dimensional Eliassen-Palm (EP) flux as a measure of the wave activity propagation, the authors show that the unusual warm years in the Arctic feature an anomalous weak stratosphere-troposphere coupling and weak downward wave flux at the lower stratosphere, especially over the North America and North Atlantic (NANA) region. The extremely cold years are characterized by strong stratosphere-troposphere coupling and strong downward wave flux in this region. The refractive index is used to examine the conception of planetary wave reflection, which shows a large refractive index (low reflection) for the extremely warm years and a small refractive index (high reflection) for the extremely cold years. This study reveals the importance of the downward planetary wave propagation from the stratosphere to the troposphere for explaining the unusual state of the stratospheric polar vortex in February.

Wave Structures in the Upper Ionospheric Plasma in Spherical Coordinates

Physical mechanism of generation of the new modes of ultra-low-frequency (ULF) electromagnetic planetary waves in F-region of the spherical ionosphere due to the latitudinal inhomogeneity of the geomagnetic field is suggested. The frequency spectra, phase velocity, and wavelength of these perturbations are determined. It is established, that these perturbations are self-localized as nonlinear solitary vortex structures in the ionosphere and moving westward or eastward along the parallels with velocities much greater than the phase velocities of the linear waves. The properties of the wave structures under investigation are very similar to those of low-frequency perturbations observed experimentally in the ionosphere at middle latitudes.

Advances in Studies of the Middle and Upper Atmosphere and Their Coupling with the Lower Atmosphere

Recent advances in studies of the middle and upper atmosphere and their coupling with the lower atmosphere in China are briefly reviewed. This review emphasizes four aspects: (1) Development of instrumentation for middle and upper atmosphere observation; (2) Analyses and observation of middle and upper atmosphere; (3) Theoretical and modeling studies of planetary wave and gravity wave activities in the middle atmosphere and their relation to lower atmospheric processes; (4) Study on the coupling between the stratosphere and the troposphere.

Decadal Variation of the Impact of La Nina on the Winter Arctic Stratosphere

The impact of La Ni?a on the winter Arctic stratosphere has thus far been an ambiguous topic of research. Contradictory results have been reported depending on the La Ni?a events considered. This study shows that this is mainly due to the decadal variation of La Ni?a’s impact on the winter Arctic stratosphere since the late 1970 s. Specifically,during the period1951–78,the tropospheric La Ni?a teleconnection exhibits a typical negative Pacific–North America pattern,which strongly inhibits the propagation of the planetary waves from the extratropical troposphere to the stratosphere,and leads to a significantly strengthened stratospheric polar vortex. In contrast,during 1979–2015,the La Ni?a teleconnection shifts eastwards,with an anomalous high concentrated in the northeastern Pacific. The destructive interference of the La Ni?a teleconnection with climatological stationary waves seen in the earlier period reduces greatly,which prevents the drastic reduction of planetary wave activities in the extratropical stratosphere. Correspondingly,the stratospheric response shows a less disturbed stratospheric polar vortex in winter.

Reponses of middle atmospheric circulation to the 2009 major sudden stratospheric warming

In this research, the roles of gravity waves and planetary waves in the change to middle atmospheric residual circulation duringa sudden stratospheric warming period are differentiated and depicted separately by adopting the downward control principle. Ouranalysis shows clear anomalous poleward residual circulation patterns from the equator to high latitudes in the lower winterstratosphere. At the same time, upward mean flows are identified at high latitudes of the winter upper stratosphere and mesosphere,which turn equatorward in the mesosphere and reach as far as the tropical region, and consequently the extratropical region in thesummer hemisphere. The downward control principle shows that anomalous mesospheric residual circulation patterns, includinginterhemispheric coupling, are solely caused by the change in gravity wave forcing resulting from the reversal of the winter stratosphericzonal wind. Nevertheless, both planetary waves and gravity waves are important to variations in the winter stratospheric circulation, butwith opposite effects.

Middle Stratospheric Polar Vortex Ozone Budget during the Warming Arctic Winter, 2002-2003

The ozone budget inside the middle stratospheric polar vortex （24-36 km） during the 2002-2003 Arctic winter is studied by analyzing Michelson Interferometer for Passive Atmospheric Sounding （MIPAS） satellite data.A comprehensive global chemical transport model （Model for Ozone and Related Chemical Tracers,MOZART-3） is used to analyze the observed variation in polar vortex ozone during the stratospheric sudden warming （SSW） events.Both MIPAS measurement and MOZART-3 calculation show that a pronounced increase （26-28 DU） in the polar vortex ozone due to the SSW events.Due to the weakening of the polar vortex,the exchange of ozone mass across the edge of the polar vortex increases substantially and amounts to about 3.0 × 10 7 kg according to MOZART-3 calculation.The enhanced downward transport offsets about 80% of polar vortex ozone mass increase by horizontal transport.A ＂passive ozone＂ experiment shows that only ～55% of the vertical ozone mass flux in February and March can be attributed to the variation in vertical transport.It is also shown that the enhanced downward ozone above ～32 km should be attributed to the springtime photochemical ozone production.Due to the increase of air temperature,the NO x reaction rate increases by 40%-80% during the SSW events.As a result,NO x catalytic cycle causes another 44% decrease in polar vortex ozone compared to the net ozone changes due to dynamical transport.It is also shown that the largest change in polar vortex ozone is due to horizontal advection by planetary waves in January 2003.

On the Formation and Maintenance of the Persistent Anomalies of Summertime Circulation over the Ural Mountains

The formation and maintenance of the persistent anomalies (PA hereafter) of summertime circulation over the Ural Mountains are studied, and a two-way interaction of transient eddies and time-mean flow that may be involved in the evolution of the positive anomaly is demonstrated. Firstly the feature of synoptic-scale transient activity during the PA period is investigated based on composite, and the results suggest a significant enhancement of transient activity over the sector from the central North Atlantic to the coastal western Europe for the positive cases whereas a weakening is for the negative. Numerical simulations are conducted using a barotropic primitive equation model linearized about two time-mean flows, the composite of positive cases and the climatological July mean respectively. The results show that the enhanced transient activity upstream will favor positive height anomalies over the Ural Mountains. A barotropic stormtrack model is developed, by which the role of time-mean flow in organization and modulation of transient eddies is studied. It is shown that the growth of ridge over the Ural Mountains tends to organize transient eddies into the region upstream from the central North Atlantic to the coastal western Europe. Combining the two aspects, a positive feedback mechanism through two-direction interaction of transient eddies and basic flow is proposed, which can be responsible for the formation and maintenance of the persistent positive anomalies over the Ural Mountains.

Three-Dimensional Dynamic Features of Two Arctic Oscillation Types

We investigated the differences between stratospheric （S-type） and tropospheric （T-type） Arctic Oscillation （AO） events on the intraseasonal time scale, in terms of their influences on surface air temperature （SAT） over the Northern Henfisphere and the dynamic features associated with their spatial structures. S-type AO events showed a stratosphere-troposphere coupled structure, while T-type events exhibited a stratosphere-troposphere uncoupled structure. The annular SAT anomalies over the Northern Hemisphere were found to be associated with S-type AO events, whereas such an annular feature was substantially de- structed in T-type AO events. The different horizontal structures in the troposphere of the two types could mainly be attributed to transient eddy feedback forcing. As for the vertically uncoupled structure of T- type events, the underlying dynamical features that differentiate them from S-type events lie in the vertical propagation of zonally confined Rossby waves. In T-type events, the zonally confined Rossby wave packets can emanate from the significant height anomalies over Northeast Asia, where one vertical waveguide exists, and then propagate upward into the stratosphere. In contrast, such a vertical propagation was not evident for S-type events. The stratospheric anomalies associated with the upward injection of the zonally confined Rossby waves from the troposphere in T-type events can further induce the anomalous vertical propagation of planetary waves （PWs） through the interference between the climatological-mean PWs and anomalous PWs, leading to the final stratosphere troposphere uncoupled structure of T-type events.