Stationary Planetary Waves Research Articles

The Wave Origins of Longitudinal Structures in ExoMars Trace Gas Orbiter (TGO) Aerobraking Densities

AbstractThe nature and origins of longitudinal density structures in Mars’ thermosphere between 100 and 120 km altitude, and −30° and −75° latitude around winter solstice (Ls = 70–122°), as measured by the accelerometer on the ExoMars Trace Gas Orbiter (TGO) Mission, are investigated. The methodology consists of deducing the responsible waves by comparing the observed longitude versus local time phase progressions of the structures with those of probable candidate waves in the Mars Climate Database (MCD) climatology. The observed wave‐1, wave‐2, and wave‐3 structures are interpreted as originating mainly from SPW1; (SPW2, S0, DE1); and (SPW3, DE2), respectively, where SPWm denotes a stationary planetary wave with zonal wavenumber s = m, S0 is the zonally symmetric semidiurnal tide, and DE1(DE2) are the eastward‐propagating diurnal tides with s = −1(−2). All of these waves exist in the MCD with amplitudes as large as those observed, although not wholly in the narrow height‐latitude regime accessed by TGO. This disparity between the MCD and TGO amplitude structures is hypothesized to result from the extreme intrusion of the polar‐region eastward winter jet into the thermosphere in the MCD. The winter polar jet blocks poleward expansion of DE1 and DE2 beyond −30° latitude, and also impacts the structures of SPW2, S0 and SPW3 that arise from in situ nonlinear interaction between DE1 and DE2, respectively, with the diurnal migrating tide (DW1).

Mutual Interference of Local Gravity Wave Forcings in the Stratosphere

Gravity wave (GW) breaking and associated GW drag is not uniformly distributed among latitudes and longitudes. In particular, regions of enhanced GW breaking, so-called GW hotspots, have been identified, major Northern Hemisphere examples being located above the Rocky Mountains, the Himalayas and the East Asian region. These hotspots influence the middle atmosphere circulation both individually and in combination. Their interference is here examined by performing simulations including (i) the respective single GW hotspots, (ii) two GW hotspots, and (iii) all three GW hotspots with a simplified global circulation model. The combined GW hotspots lead to a modification of the polar vortex in connection with a zonal mean flow decrease and an increase of the temperature at higher latitudes. The different combinations of GW hotspots mainly prevent the stationary planetary wave (SPW) 1 from propagating upward at midlatitudes leading to a decrease in energy and momentum transfer in the middle atmosphere caused by breaking SPW 1, and in turn to an acceleration of the zonal mean flow at lower latitudes. In contrast, the GW hotspot above the Rocky Mountains alone causes an increase in SPW 1 amplitude and Eliassen–Palm flux (EP flux), inducing enhanced negative EP divergence, decelerating the zonal mean flow at higher latitudes. Consequently, none of the combinations of different GW hotspots is comparable to the impact of the Rocky Mountains GW hotspot alone. The reason is that the GW hotspots mostly interfere nonlinearly. Depending on the longitudinal distance between two GW hotspots, the interference between the combined Rocky Mountains and East Asian GW hotspots is more additive than the interference between the combined Rocky Mountains and Himalaya GW hotspots. While the Rocky Mountains and the East Asian GW hotspots are longitudinally displaced by 105°, the Rocky Mountains are shifted by 170° to the Himalayas. Moreover, while the East Asian and the Himalayas are located side by side, the interference between these GW hotspots is the most nonlinear because they are latitudinally displaced by 20°. In general, the SPW activity, e.g., represented in SPW amplitudes, EP flux or Plumb flux, is strongly reduced, when the GW hotspots are interacting with each other. Thus, the interfering GW hotspots mostly have a destructive effect on SPW propagation and generation.

Comparison of Key Characteristics of Remarkable SSW Events in the Southern and Northern Hemisphere

An exceptionally strong sudden stratospheric warming (SSW) in the Southern Hemisphere (SH) during September 2019 was observed. Because SSW in the SH is very rare, comparison with the only recorded major SH SSW is done. According to World Meteorological Organization (WMO) definition, the SSW in 2019 has to be classified as minor. The cause of SSW in 2002 was very strong activity of stationary planetary wave with zonal wave-number (ZW) 2, which reached its maximum when the polar vortex split into two circulations with polar temperature enhancement by 30 K/week and it penetrated deeply to the lower stratosphere and upper troposphere. On the other hand, the minor SSW in 2019 involved an exceptionally strong wave-1 planetary wave and a large polar temperature enhancement by 50.8 K/week, but it affected mainly the middle and upper stratosphere. The strongest SSW in the Northern Hemisphere was observed in 2009. This study provides comparison of two strongest SSW in the SH and the strongest SSW in the NH to show difference between two hemispheres and possible impact to the lower or higher layers.

Solar Tides in the Middle and Upper Atmosphere of Mars

AbstractSolar tides are responsible for much of the spatial‐temporal variability of Mars' upper atmosphere (100–∼200 km). However, the tidal spectrum, its latitude versus Ls variability, and its vertical evolution remain uncertain. In this paper, Mars Climate Sounder temperature measurements at 76 km above Mars' areoid are used to construct a multiyear latitude versus Ls climatology of the tidal spectrum. The most important spectral components include the solar‐synchronous (“migrating”) components DW1, SW2, and the solar‐asynchronous (“nonmigrating”) tides DE3, DE2, DE1, SE1, S0, and SW1. The Mars Climate Database (MCD), which provides predictions from the Laboratoire de Météorologie Dynamique Global Climate Model, captures particularly well the amplitudes and key structural features of the solar‐asynchronous tides at 76 km that furthermore underly the large longitudinal structures in density that are observed between 100 and 200 km. Height‐latitude and latitude‐Ls structures of MCD density perturbations are therefore examined between 76 and 172 km and interpreted in terms of mean wind and dissipation effects. In particular, due to the smaller radius and more intense zonal‐mean zonal winds at Mars compared to Earth, Doppler‐shift effects are significantly exaggerated compared to Earth. Evidence is also provided for nonnegligible contributions to density variability from stationary planetary waves which arise from tide‐tide nonlinear interactions. It is moreover shown that MCD captures the salient amplitude and phase characteristics of the ∼±30–60% longitudinal density perturbations measured by the Mars Global Surveyor accelerometer. This, and the excellent MCD‐MCS agreement at 76 km, lends credibility to the ability of MCD to provide new insights into thermosphere density variability at Mars due to vertical coupling by solar tides.

Amplitude modulation of the semidiurnal tide based on MLT wind measurements with a European/Siberian meteor radar network in October – December 2017

We present results on temporal and longitudinal modulations of semidiurnal tide amplitudes in the mesosphere and lower thermosphere winds. The wind data were obtained during October – December 2017 when six meteor radars operated simultaneously. The radar network covers latitudes from 51°N to 72°N and longitudes from 13°E to 178°E. The results show a clear tidal 8–9 day amplitude modulation, which significantly changes with latitude. Evidence is provided for a non-linear interaction between the semidiurnal tide and eastward and westward propagating planetary waves as a source of the modulation. The modulation from the interaction with eastward propagating waves of zonal wavenumber 1 is observed at high latitudes (65°–72°N). A modulation in correspondence with non-linear interaction with a westward propagating wave of zonal wavenumber 1 replaces the first one at middle latitudes (51°–52°N). Furthermore, we found a significant statistical link between the upper stratosphere zonal jet oscillations and the longitudinal difference in tidal amplitudes obtained at the Collm and Angarsk mid-latitude stations. The correlation coefficients are about 0.61 and 0.55 for zonal and meridional amplitudes, respectively. The difference between tidal winds taken at different longitudes grows in amplitude for both wind components at middle latitudes during the increase of stationary planetary wave 1 activity in December. TIDI upper mesospheric wind data indicate a semidiurnal westward propagating tide with wavenumber 3 as the leading source of this effect. The difference between tidal winds at high-latitudes shows different behaviour for the zonal and meridional wind components in December.

Migrating and non-migrating tides observed in the stratosphere from FORMOSAT-3/COSMIC temperature retrievals

Abstract. Formosa Satellite-3 and Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC) temperature data during October 2009–December 2010 are analysed for tides in the middle atmosphere from ∼10 to 50 km. COSMIC is a set of six micro-satellites in near-Sun-synchronous orbits with 30∘ orbital separations that provides good phase space sampling of tides. Short-term tidal variability is deduced by considering ±10 d data together. The migrating diurnal (DW1) tide is found to peak over the Equator at 30 km. It maximises and slightly shifts poleward during winters. Over middle and high latitudes, DW1 and the non-migrating diurnal tides with wavenumber 0 (DS0) and wavenumber 2 (DW2) are intermittent in nature. Numerical experiments in the current study show that these could be a result of aliasing as they are found to occur at times of a steep rise or fall in the mean temperature, particularly during the sudden stratospheric warming (SSW) of 2010. Further, the stationary planetary wave component of wavenumber 1 (SPW1) is found to be of very large amplitudes in the Northern Hemisphere, reaching 18 K at 30 km over 65∘ N. By using data from COSMIC over shorter durations, it is shown that aliasing between stationary planetary wave and non-migrating tides is reduced and thus results in the large amplitudes of the former. This study clearly indicates that non-linear interactions are not a very important source for the generation of non-migrating tides in the middle- and high-latitude winter stratosphere. There is also a modulation of SPW1 by a ∼60 d oscillation in the high latitudes, which was not seen earlier.

A Warm Layer in the Nightside Mesosphere of Mars

AbstractWe report a new set of stellar occultation measurements for nightside temperature profiles made by the Mars Atmosphere and Volatile EvolutioN/Imaging Ultraviolet Spectrograph that provide evidence for a recurring layer of warm air between 70 and 90 km altitudes in the nightside mesosphere of Mars during Ls = 0–180° in Martian Year 33–34. The nightside profiles reveal a recurring peak of atmospheric temperature around 80 km over the equator to the middle latitudes in the northern hemisphere. The predictions of the Mars Climate Database have a warm layer with much smaller amplitudes. The observed peak amplitudes are larger than those predicted by the model by up to 90 K. Wavenumber‐3 structures are seen in the warm layer that are potentially signatures of thermal tides or stationary planetary waves, with amplitudes two times larger than predicted.

Impact of local gravity wave forcing in the lower stratosphere on the polar vortex stability: effect of longitudinal displacement

Abstract. The effects of gravity wave (GW) breaking hotspots in the lower stratosphere, especially the role of their longitudinal distribution, are evaluated through a sensitivity study by using a simplified middle atmosphere circulation model. For the position of the local GW hotspot, we first selected a fixed latitude range between 37.5 and 62.5∘ N and a longitude range from 112.5 to 168.75∘ E, as well as an altitude range between 18 and 30 km. This confined GW hotspot was then shifted in longitude by 45∘ steps, so that we created eight artificial GW hotspots in total. Strongly dependent on the location of the respective GW hotspot with regard to the phase of the stationary planetary wave of wavenumber 1 (SPW 1) generated in the model, the local GW forcing may interfere constructively or destructively with the modeled SPW 1. GW hotspots, which are located in North America near the Rocky Mountains, lead to an increase in the SPW 1 amplitude and EP flux, while hotspots located near the Caucasus, the Himalayas or the Scandinavian region lead to a decrease in these parameters. Thus, the polar vortex is less (Caucasus and Himalayan hotspots) or more weakened (Rocky Mountains hotspot) by the prevailing SPW activity. Because the local GW forcing generally suppresses wave propagation at midlatitudes, the SPWs 1 propagate into the polar region, where the refractive index turned to positive values for the majority of the artificial GW hotspots. An additional source of SPW 1 may be local instabilities indicated by the reversal in the meridional potential vorticity gradient in the polar region in connection with a positive EP divergence. In most cases, the SPWs 1 are breaking in the polar region and maintain the deceleration and, thus, the weakening of the polar vortex. While the SPWs 1 that form when the GW hotspots are located above North America propagate through the polar region into the middle atmosphere, the SPWs 1 in the remaining GW hotspot simulations were not able to propagate further upwards because of a negative refractive index above the positive refractive index anomaly in the polar region. GW hotspots, which are located near the Himalayas, influence the mesosphere–lower thermosphere region because of possible local instabilities in the lower mesosphere generating additional SPWs 1, which propagate upwards into the mesosphere.

September 2019 Antarctic Sudden Stratospheric Warming: Quasi‐6‐Day Wave Burst and Ionospheric Effects

AbstractAn exceptionally strong stationary planetary wave with Zonal Wavenumber 1 led to a sudden stratospheric warming (SSW) in the Southern Hemisphere in September 2019. Ionospheric data from European Space Agency's Swarm satellite constellation mission show prominent 6‐day variations in the dayside low‐latitude region at this time, which can be attributed to forcing from the middle atmosphere by the Rossby normal mode “quasi‐6‐day wave” (Q6DW). Geopotential height measurements by the Microwave Limb Sounder aboard National Aeronautics and Space Administration's Aura satellite reveal a burst of global Q6DW activity in the mesosphere and lower thermosphere during the SSW, which is one of the strongest in the record. The Q6DW is apparently generated in the polar stratosphere at 30–40 km, where the atmosphere is unstable due to strong vertical wind shear connected with planetary wave breaking. These results suggest that an Antarctic SSW can lead to ionospheric variability through wave forcing from the middle atmosphere.

Tropospheric circulation response to sudden stratospheric warming observed in January 2013

Analysis of the dynamical regime changes in the stratosphere during different phases of the Sudden Stratospheric Warming (SSW) that has been observed in January 2013 is presented. The different mechanisms of SSW influence on the tropospheric circulation through the stationary planetary waves (SPWs) reflection and/or increase in SPWs activity due to nonlinear interaction with the mean flow and their subsequent propagation into the troposphere are discussed. Three-dimensional wave activity flux and its divergence are determined using the UK Met Office data; the synoptic situation and its changes during the SSW events are analyzed. The wave activity penetrates downward from stratosphere into the troposphere and can affect weather processes during the SSW and right afterwards. It is this time that polar anticyclones can be formed at high latitudes, which quickly go southward along meridional directions and then deviate to the East at middle latitudes. Interestingly, the locations of polar anticyclone formations and subsequent displacements correspond to the regions of maximal horizontal wave activity fluxes connected with stratospheric processes. The results obtained allow us to suggest that accounting of stratospheric processes and their influence on the troposphere in winter season can improve the middle-range forecast of anticyclone formation and cold weather events at middle latitudes.

Reactions of the Middle Atmosphere Circulation and Stationary Planetary Waves on the Solar Activity Effects in the Thermosphere

AbstractUsing numerical simulations of the general atmospheric circulation during boreal winter, statistically confident evidences are obtained for the first time, demonstrating that changes in the solar activity (SA) in the thermosphere at heights above 100 km can influence propagation and reflection conditions for stationary planetary waves (SPWs) and can modify the middle atmosphere circulation below 100 km. A numerical mechanistic model simulating atmospheric circulation and SPWs at heights 0–300 km is used. To achieve sufficient statistical confidence, 80 pairs of 15‐day intervals were extracted from an ensemble of 16 pairs of model runs corresponding to low and high SA. Results averaged over these intervals show that impacts of SA above 100 km change the mean zonal wind and temperature up to 10% at altitudes below 100 km. The statistically confident changes in SPW amplitudes due to SA impacts above 100 km reach up to 50% in the thermosphere and 10–15% in the middle atmosphere depending on zonal wavenumber. Changes in wave amplitudes correspond to variations of the Eliassen‐Palm flux and may alter dynamical and thermal SPW impacts on the mean wind and temperature. Thus, variable conditions of SPW propagation and reflection at thermospheric altitudes may influence the middle atmosphere circulation, thermal structure, and planetary waves.

Nonlinear interactions of stationary planetary waves during February 2016 sudden stratospheric warming

An analysis of nonlinear wave-wave and wave-mean flow interactions has been carried out during a sudden stratospheric warming (SSW) event in February 2016. This approach is based on a study of the perturbed potential enstrophy (Ertel’s potential vorticity squared) balance equation. The results obtained by using UK Met Office reanalysis data are presented. It has been shown that an increase in the nonlinear interactions occurs at higher-middle latitudes of the boreal stratosphere during the SSW. It is noted that it is necessary to include the stationary planetary wave with zonal wave number m=3 in the analysis of major warmings.

Tropical Deep Convection Impact on Southern Winter Stationary Waves and Its Modulation by the Quasi-Biennial Oscillation

Abstract The impact of tropical deep convection on southern winter stationary waves and its modulation by the quasi-biennial oscillation (QBO) have been investigated in a long (210 year) climate model simulation and in ERA-Interim reanalysis data for the period 1979–2018. Model results reveal that tropical deep convection over the region of its climatological maximum modulates high-latitude stationary planetary waves in the southern winter hemisphere, corroborating the dominant role of tropical thermal forcing in the generation of these waves. In the tropics, deep convection enhancement leads to wavenumber-1 eddy anomalies that reinforce the climatological Rossby–Kelvin wave couplet. The Rossby wave propagates toward the extratropical southern winter hemisphere and upward through the winter stratosphere reinforcing wavenumber-1 climatological eddies. As a consequence, stronger tropical deep convection is related to greater upward wave propagation and, consequently, to a stronger Brewer–Dobson circulation and a warmer polar winter stratosphere. This linkage between tropical deep convection and the Southern Hemisphere (SH) winter polar vortex is also found in the ERA-Interim reanalysis. Furthermore, model results indicate that the enhancement of deep convection observed during the easterly phase of the QBO (E-QBO) gives rise to a similar modulation of the southern winter extratropical stratosphere, which suggests that the QBO modulation of convection plays a fundamental role in the transmission of the QBO signature to the southern stratosphere during the austral winter, revealing a new pathway for the QBO–SH polar vortex connection. ERA-Interim corroborates a QBO modulation of deep convection; however, the shorter data record does not allow us to assess its possible impact on the SH polar vortex.

Precursor in Arctic oscillation for the East Asian January temperature and its relationship with stationary planetary waves: Results from CMIP5 models

AbstractThe emerging precursor in December Arctic oscillation (AO) for the following January temperature over East Asia (TEA) has been noticed by recent researches. This study evaluates the precursor in December AO for the following January TEA using 35 climate models from the Coupled Model Intercomparison Project Phase 5. Results indicate that, 24 (multi‐model ensemble mean; MME‐GOOD) out of total 35 models reproduce the statistically significant positive correlation between the December AO and the January TEA identified in the observation, but the remaining 11 models (MME‐BAD) fail. Further, the investigation focuses on these models' simulations for the December AO‐associated atmospheric circulation in January. Eighteen (MME‐GOOD‐18) out of the above 24 models reproduce the persistence of December AO‐related atmospheric circulation, including the seesaw structure of the sea level pressure anomalies, the sweeping southerly 850‐hPa wind anomalies over the East Asia–Northwest Pacific region, the weakening of the East Asian trough, and the weakened meridional shear of the East Asian jet stream in January following an enhanced December AO. It is found that the propagation of stationary planetary waves plays a crucial role in connecting the December AO and the January TEA. Therefore, the models' ability to simulate the stratosphere–troposphere interaction is essential for the successful simulations on the persistence of December AO. Additionally, the future projections indicate that the precursor in December AO for the following January TEA is still robust during the 21st century.

Effect of latitudinally displaced gravity wave forcing in the lower stratosphere on the polar vortex stability

Abstract. In order to investigate the impact of a locally confined gravity wave (GW) hotspot, a sensitivity study based on simulations of the middle atmosphere circulation during northern winter was performed with a nonlinear, mechanistic, general circulation model. To this end, we selected a fixed longitude range in the East Asian region (120–170∘ E) and a latitude range from 22.5 to 52.5∘ N between 18 and 30 km for the hotspot region, which was then shifted northward in steps of 5∘. For the southernmost hotspots, we observe a decreased stationary planetary wave (SPW) with wave number 1 (SPW 1) activity in the upper stratosphere and lower mesosphere, i.e., fewer SPWs 1 are propagating upwards. These GW hotspots lead to a negative refractive index, inhibiting SPW propagation at midlatitudes. The decreased SPW 1 activity is connected to an increased zonal mean zonal wind at lower latitudes. This, in turn, decreases the meridional potential vorticity gradient (qy) from midlatitudes towards the polar region. A reversed qy indicates local baroclinic instability, which generates SPWs with wave number 1 in the polar region, where we observe a strong positive Eliassen–Palm (EP) divergence. As a result, the EP flux increases towards the polar stratosphere (corresponding to enhanced SPW 1 amplitudes), where the SPWs with wave number 1 break, and the zonal mean zonal wind decreases. Thus, the local GW forcing leads to a displacement of the polar vortex towards lower latitudes. The effect of the local baroclinic instability indicated by the reversed qy also produces SPWs with wave number 1 in the lower mesosphere. The effect on the dynamics in the middle atmosphere due to GW hotspots that are located northward of 50∘ N is negligible, as the refractive index of the atmosphere is strongly negative in the polar region. Thus, any changes in the SPW activity due to the local GW forcing are quite ineffective.

Solar-wind-magnetosphere energy influences the interannual variability of the northern-hemispheric winter climate.

Solar irradiance has been universally acknowledged to be dominant by quasi-decadal variability, which has been adopted frequently to investigate its effect on climate decadal variability. As one major terrestrial energy source, solar-wind energy flux into Earth's magnetosphere (Ein) exhibits dramatic interannual variation, the effect of which on Earth's climate, however, has not drawn much attention. Based on the Ein estimated by 3D magnetohydrodynamic simulations, we demonstrate a novelty that the annual mean Ein can explain up to 25% total interannual variance of the northern-hemispheric temperature in the subsequent boreal winter. The concurrent anomalous atmospheric circulation resembles the positive phase of Arctic Oscillation/North Atlantic Oscillation. The warm anomalies in the tropic stratopause and tropopause induced by increased solar-wind–magnetosphere energy persist into the subsequent winter. Due to the dominant change in the polar vortex and mid-latitude westerly in boreal winter, a ‘top-down’ propagation of the stationary planetary wave emerges in the Northern Hemisphere and further influences the atmospheric circulation and climate.

Atmospheric Tides at High Latitudes in the Martian Upper Atmosphere Observed by MAVEN and MRO

AbstractGlobal‐scale waves have been seen throughout the Martian atmosphere and can achieve significant amplitude at higher altitudes. Previous observations of the upper atmosphere have also revealed wavenumber‐3 signatures with significant amplitudes that have been interpreted as signatures of diurnal and semidiurnal tides or stationary planetary waves. This study focuses on two intervals during which concurrent observations of the upper thermosphere made in situ, the middle thermosphere made remotely, and the middle atmosphere made remotely provide observations of the atmospheric tides between 50‐ and 200‐km altitude. Focusing on high latitudes, these observations are able to identify strong wavenumber‐3 signatures in the thermosphere that propagate eastward with increasing local time, consistent with an eastward propagating tide. A complementary analysis of the data from the middle atmosphere reveals wavenumber‐3 signatures that move eastward and upward. During the first interval, these analyses reveal a combination of the diurnal tide DE2 and the semidiurnal tide SE1 to be present, while during the second only the semidiurnal SE1 is seen. During both intervals, the observations provide a consistent picture of these waves being present from the middle atmosphere to the upper thermosphere, consistent with the theory that such waves are generated in the lower atmosphere and propagate upward throughout the entire atmosphere.

El Ni\xf1o\u2013Southern Oscillation effect on ionospheric tidal/SPW amplitude in 2007\u20132015 FORMOSAT-3/COSMIC observations

This study examines the influence of the El Niño–Southern Oscillation (ENSO) on the ionospheric total electron content (TEC) diurnal eastward 3 (DE3) and stationary planetary wave 4 (SPW4) which are the major components of the ionospheric wave-4 longitudinal structure. The TEC is the integration of electron density from 200 to 800 km sounded by the GPS radio occultation experiment onboard the FORMOSAT-3/COSMIC satellites during the period of January 2007–December 2015. The results show that the TEC DE3 and SPW4 amplitudes respond to the ENSO signature in the thermospheric wind DE3 in the Northern Hemisphere during the lower-solar-activity period. The contribution of the ENSO cold phase in 2010 and 2011 to the quasi-biennial oscillation in the TEC DE3 and SPW4 amplitudes is not negligible.

Formulation of Three-Dimensional Quasi-Residual Mean Flow Balanced with Diabatic Heating Rate and Potential Vorticity Flux

Abstract Three-dimensional (3D) quasi-residual mean flow is derived to diagnose 3D dynamical material transport associated with stationary planetary waves. The 3D quasi-residual mean vertical flow does not include the vertical flow due to tilting of the potential temperature caused by stationary waves, which is apparent but not seen in the mass-weighted isentropic mean state. Thus, the quasi-residual mean vertical flow is balanced with the term of diabatic heating rate. The 3D quasi-residual mean horizontal flow is balanced with the sum of the forcing due to transient wave activity flux divergence and the forcing associated with fluctuation of the potential vorticity due to stationary waves (defined as the effective Coriolis forcing). The zonal mean of the effective Coriolis forcing corresponds to the divergence of stationary wave activity flux. Thus, the zonal mean of derived 3D quasi-residual mean flow is exactly equal to the traditional residual mean flow. To demonstrate the usefulness of this quasi-residual mean flow, we analyze material transport of atmospheric sulfur hexafluoride (SF6) by using an atmospheric chemistry transport model. Comparison between the derived 3D quasi-residual mean flow and traditional residual mean flow shows that the zonal mean of advection of SF6 associated with the 3D quasi-residual mean flow derived is almost equal to that of the traditional residual mean flow. Next, it is confirmed that the horizontal structure of advection of SF6 associated with the 3D quasi-residual mean flow is balanced with the transport because of the nonlinear, nonconservative effects of disturbances. This relation is similar to the results for traditional residual mean flow in the zonal-mean state.

A Statistical Approach to Quantify Atmospheric Contributions to the ITEC WN4 Structure Over Low Latitudes

AbstractBased on multiyear observations of ionospheric total electron content (TEC) and atmospheric wind, we develop a new method to interpret the atmospheric contribution to the ionospheric wave number‐4 (WN4) structure according to their coherences in annual variations. First, the ionospheric WN4 is extracted from the equatorial integrated TEC (ITEC) using the global ionospheric maps. The wind observation from the TIMED Doppler Interferometer on board the Thermosphere Ionosphere Mesosphere Energetic and Dynamics (TIMED) satellite are used to deduce the latitudinal symmetric and antisymmetric components of the zonal and meridional DE3 (diurnal, eastward, and zonal wave number 3), SE2 (semidiurnal, eastward, and zonal wave number 2), and SPW4 (stationary planetary wave with zonal wave number 4). We then develop a regression model to estimate the coupling efficiency, the background diurnal influence, and the associated contribution in ITEC WN4. (1) The zonal symmetric DE3 is the most efficient tide in generating ITEC WN4, while the zonal symmetric SPW4 plays a secondary but varied role. (2) The diurnal variation of background ionosphere/thermosphere influence's amplitude is similar to that of the zonal mean ITEC during the day, with a westward phase velocity. (3) The zonal symmetric DE3 resulted WN4 can reach 7% of the zonal daily mean ITEC, while the observed total WN4 value is about 10%. The contributions by the zonal symmetric SE2, SPW4, and meridional symmetric SE2 are comparable with respective maxima ~1.5% of the zonal daily mean ITEC. The present results confirm former suggestions that symmetric zonal DE3 is the primary source for ionospheric WN4, and the contributions due to antisymmetric wind components are relatively small in ITEC WN4.