Zonal Wind Oscillation Research Articles

Zonal Asymmetry of the QBO Temperature Signal in the Tropical Tropopause Region

AbstractThe quasi‐biennial oscillation (QBO) of the equatorial zonal wind leads to zonally symmetric temperature variations in the stratosphere that descend downward. Here we investigate the QBO‐induced temperature anomalies in the tropical tropopause layer (TTL) and detect pronounced longitudinal variations of the signal. In addition, the QBO temperature anomalies show a strong seasonal variability. The magnitude of these seasonal and longitudinal QBO variations is comparable to the magnitude of the well‐known zonal mean QBO signal in the TTL. At the cold point tropopause, the strongest QBO variations of around ±1.6 K are found over regions of active convection such as the West Pacific and Africa during boreal winter. The weakest QBO variations of ±0.25 K are detected over the East Pacific during boreal summer, while the zonal mean signal ranges around ±0.7 K. The longitudinal variations are associated with enhanced convective activity that occurs during QBO cold phases and locally enhances the cold anomalies.

Progress in Simulating the Quasi‐Biennial Oscillation in CMIP Models

AbstractThe quasi‐biennial oscillation (QBO) of the zonal mean zonal wind is the primary mode of variability in the tropical lower stratosphere. The QBO is characterized by alternating easterly westerly shear layers that descend down from ∼10 to 100 hPa. The QBO is also seen in lower stratospheric tropical temperature, water vapor, and ozone and affects tropospheric variability through various teleconnections. We examine here the progress in simulating the QBO in the Coupled Model Intercomparison Project (CMIP) models, more specifically in CMIP3, CMIP5, and CMIP6 models. We show that the number of models that are able to simulate the QBO has increased from 0 in CMIP3, to 5 in CMIP5, to 15 in CMIP6. While the number of models with an internally generated QBO has tripled from CMIP5 to CMIP6, the fidelity of the simulation averaged over the CMIP models has not improved. We show that CMIP5 and CMIP6 models represent the QBO period and latitudinal extent quite well; however the QBO amplitude is shifted upwards relative to observations resulting in large underestimation of QBO amplitude at all levels below 20 hPa. The underestimation of QBO amplitude in the lowermost stratosphere and lack of variations downward to the tropopause and below will likely impact the quality of teleconnections seen in the current generation Earth system models.

The influence of the stratospheric Quasi-Biennial Oscillation on trace gas levels at the Earth’s surface

The Quasi-Biennial Oscillation (QBO) of tropical zonal wind is one of the most important modes of interannual variability in the stratosphere. It is well established that the QBO influences the distribution of trace gases throughout the global stratosphere. What has not been clearly shown thus far is whether the stratospheric QBO has a consistent and significant impact on tropospheric trace gases. Here we clearly demonstrate that the effects of QBO variability in stratospheric transport and trace gas distributions regularly and persistently extend into the troposphere, which influences the interannual variability of long-lived trace gas mole fractions at the Earth’s surface. We show that the variability in the surface mole fractions on one- to five-year timescales is primarily driven by the QBO. The QBO influence on tropospheric constituent mole fractions arises from the modulation of the stratosphere to troposphere mass flux and is apparent in surface measurements, as well as throughout the stratosphere and troposphere in chemistry–climate model simulations of chlorofluorocarbon-11, chlorofluorocarbon-12 and nitrous oxide. The global total emissions estimated from measured changes in the global mean surface mole fractions of these ozone-depleting species, as well as other long-lived trace gases, will be improved by accurately accounting for the QBO-driven variability. Interannual variations of long-lived trace gas mole fractions at the Earth’s surface are primarily driven by the stratospheric Quasi-Biennial Oscillation, according to surface measurements and model simulations. Ignoring this variability may induce errors in estimating emissions of trace gases.

Improved Simulation of the QBO in E3SMv1

AbstractThe quasi‐biennial oscillation (QBO) of the zonal mean wind is a prominent feature of the tropical lower stratosphere and has been shown to influence stratospheric and tropospheric variability. Although observed for many decades, the QBO is difficult to be accurately captured in Earth system models. The newly developed U.S. Department of Energy Energy Exascale Earth System Model, Version 1 (E3SMv1) is capable of resolving stratospheric dynamics as it has a top at 0.1 hPa and 72 levels. The tropical oscillation of the zonal mean zonal wind in the default version of the model is too fast and too strong compared to the observed QBO. Here we evaluate the current simulation of the QBO and present simulations with modified convective gravity wave parameterization parameters that make the oscillation more realistic, especially in terms of the period. Although improvements in the QBO are obtained through modifications to the parameterized gravity waves, we find that the forcing of the QBO from Kelvin and mixed‐Rossby gravity waves is small due to weak sources in the troposphere. The changes to the parameterized convective gravity waves (and QBO) are primarily limited to the tropical stratosphere. Small changes to mean wind and temperature are also found in Northern Hemisphere winter in the uppermost troposphere between 10°N and 60°N. Modifications to parameterized convectively generated gravity waves result in changes in interannual variability, primarily in the Southern Hemisphere, and modest changes in sea level pressure variability over the Pacific are also noted.

The characteristics of ozone concentration over the maritime equatorial stratospheric region derived from the quasi-biennial oscillation

The characteristics of ozone concentration [O3] over the Maritime Equatorial Stratospheric region until now are not yet fully understood well due to the limitation of data observations. However, there are many techniques to derive ozone concentration data; from satellite, in-situ observation, modeling, etc. We have investigated, then found a good agreement between the characteristics of ozone concentration and Quasi-Biennial Oscillation (QBO). This study mainly concerned with the analysis of the stratospheric zonal wind from Singapore’s QBO monthly data at 100-10 hPa layers. Total ozone, ozone mass mixing ratio, and stratospheric temperature were considered in the analysis. Predominant peak oscillation in each layer was investigated by using the spectral technique. The result shows that a strong signal of zonal wind oscillation pattern was evident at 30 hPa layer. As the altitude decreases, zonal wind oscillation decays. Box-Jenkins final model contained 28 months of a seasonal component (5,0,4)(0,1,0)28 and a percentage error of 46.6%, whereas multiple linear regression obtained a quite good correlation score, which was about 0.55.

Investigating the semiannual oscillation on Mars using data assimilation

A Martian semiannual oscillation (SAO), similar to that in the Earth’s tropical stratosphere, is evident in the Mars Analysis Correction Data Assimilation reanalysis dataset (MACDA) version 1.0, not only in the tropics, but also extending to higher latitudes. Unlike on Earth, the Martian SAO is found not always to reverse its zonal wind direction, but only manifests itself as a deceleration of the dominant wind at certain pressure levels and latitudes. Singular System Analysis (SSA) is further applied on the zonal-mean zonal wind in different latitude bands to reveal the characteristics of SAO phenomena at different latitudes. The second pair of principal components (PCs) is usually dominated by a SAO signal, though the SAO signal can be strong enough to manifest itself also in the first pair of PCs. An analysis of terms in the Transformed Eulerian Mean equation (TEM) is applied in the tropics to further elucidate the forcing processes driving the tendency of the zonal-mean zonal wind. The zonal-mean meridional advection is found to correlate strongly with the observed oscillations of zonal-mean zonal wind, and supplies the majority of the westward (retrograde) forcing in the SAO cycle. The forcing due to various non-zonal waves supplies forcing to the zonal-mean zonal wind that is nearly the opposite of the forcing due to meridional advection above ∼3 Pa altitude, but it also partly supports the SAO between 40 Pa and 3 Pa. Some distinctive features occurring during the period of the Mars year (MY) 25 global-scale dust storm (GDS) are also notable in our diagnostic results with substantially stronger values of eastward and westward momentum in the second half of MY 25 and stronger forcing due to vertical advection, transient waves and thermal tides.Mars; Mars, atmosphere; Mars, climate; Atmospheres, dynamics; Atmospheres, structure; Meteorology.

On one technique of the analysis of oscillation processes for the geophysical problems

A technique is proposed for evolution equation that estimates the impact of different terms in phase change for oscillations with different frequencies. The impact is normalized in such way that sum of impacts for all terms equals 1. Proposed technique is applied for study of quasibiannual oscillation of zonal wind in equatorial stratosphere produced in 500 year preindustrial run with climate model of Institute of Numerical Mathematics RAS. The impact of nonorographic and orographic gravity wave drag and advection by zonal mean vertical wind to the phase change of model quasibiannual oscillation. It is shown that nonorographic wave drag is main mechanism responsible for phase change (the impact equals 1.58), vertical advection slows down phase change (impact is –0.74), and the impacts of other terms are small.

Quasi-Biennial Oscillations in Atmospheric Ozone from the Chemistry-Climate Model and Ozone Reanalysis

The quasi-biennial oscillation is the primary mode of variability of the equatorial mean zonal wind in the lower stratosphere, which is characterized by downward propagating easterly and westerly wind regimes from 10 hPa level with a period approximately 28 months. The effects of the stratospheric quasi-biennial oscillation in zonal winds (SQBO) are not only confined to atmospheric dynamics but also seen in the chemical constituent (trace gases) anomalies such as ozone, water vapor, carbon monoxide and methane in the lower stratosphere. In this study, we examined the SQBO and associated ozone quasi-biennial oscillation (OQBO) using the chemistry-climate model CHASER (MIROC-ESM) simulations and ECMWF ERA-Interim ozone reanalysis for the period 2000-2015. We used lower stratospheric zonal wind from the radiosonde observations and total column ozone (TCO) from Aura Satellite (OMI Instruments) over Singapore to compare the SQBO and OQBO phases with model and reanalysis. The SQBO shows large variations in magnitude and periodicity during the period of study and the amplitude of OQBO also changes in accordance with the westerly (+ve ozone anomaly) and easterly (-ve ozone anomaly) phases of SQBO. During the Westerly phase of Ozone QBO (WQBO) corresponds to average positive total ozone anomaly of ~10 DU and in the Easterly phase of Ozone QBO (EQBO) corresponds to an average negative total ozone anomaly ~−10 DU in the tropical lower stratosphere. Since the SQBO phases were explained by the vertical propagations of Mixed-Ross by Gravity (MRG) waves and Kelvin waves, the correlation of ozone volume mixing ratio with zonal and vertical velocities gives quasi-biennial signals, which indicate the OQBO mechanism more related to dynamical transport than the stratospheric photochemical variations. Since the average amplitude of OQBO phases gives ~+/− 10 DU from the observations during easterly and westerly phases SQBO, we need more research focused on the dynamical transport than the photochemical changes to understand the tropical ozone variability due to the ozone quasi-biennial oscillations.

LOW-FREQUENCY CIRCULATION AND EXTENDED-RANGE FORECAST IN CONNECTION WITH AUTUMN EXTREME HEAVY RAINFALL PROCESS IN HAINAN

Observed daily precipitation data from the National Meteorological Observatory in Hainan province and daily data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis-2 dataset from 1981 to 2014 are used to analyze the relationship between Hainan extreme heavy rainfall processes in autumn (referred to as EHRPs) and 10–C30 d low-frequency circulation. Based on the key low-frequency signals and the NCEP Climate Forecast System Version 2 (CFSv2) model forecasting products, a dynamical-statistical method is established for the extended-range forecast of EHRPs. The results suggest that EHRPs have a close relationship with the 10–C30 d low-frequency oscillation of 850 hPa zonal wind over Hainan Island and to its north, and that they basically occur during the trough phase of the low-frequency oscillation of zonal wind. The latitudinal propagation of the low-frequency wave train in the middle-high latitudes and the meridional propagation of the low-frequency wave train along the coast of East Asia contribute to the ‘north high (cold), south low (warm)’ pattern near Hainan Island, which results in the zonal wind over Hainan Island and to its north reaching its trough, consequently leading to EHRPs. Considering the link between low-frequency circulation and EHRPs, a low-frequency wave train index (LWTI) is defined and adopted to forecast EHRPs by using NCEP CFSv2 forecasting products. EHRPs are predicted to occur during peak phases of LWTI with value larger than 1 for three or more consecutive forecast days. Hindcast experiments for EHRPs in 2015–C2016 indicate that EHRPs can be predicted 8–C24 d in advance, with an average period of validity of 16.7 d.

The importance of stratospheric initial conditions for winter North Atlantic Oscillation predictability and implications for the signal‐to‐noise paradox

This study investigates the influence of atmospheric initial conditions on winter seasonal forecasts of the North Atlantic Oscillation (NAO). Hindcast (or reforecast) experiments – which differ only in their initial conditions – are performed over the period 1960–2009, using prescribed sea surface temperature (SST) and sea‐ice boundary conditions. The first experiment (“ERA‐40/Int IC”) is initialized using the ERA‐40 and ERA‐Interim reanalysis datasets, which assimilate upper‐air, satellite and surface observations; the second experiment (“ERA‐20C IC”) is initialized using the ERA‐20C reanalysis dataset, which assimilates only surface observations. The ensemble mean NAO skill is largest in ERA‐40/Int IC (r= 0.54), which is initialized with the superior reanalysis data. Moreover, ERA‐20C IC did not exhibit significantly more NAO hindcast skill (r= 0.38) than in a third experiment, which was initialized with incorrect (shuffled) initial conditions. The ERA‐40/Interim and ERA‐20C initial conditions differ substantially in the tropical stratosphere, where the quasi‐biennial oscillation (QBO) of zonal winds is not present in ERA‐20C. The QBO hindcasts are highly skilful in ERA‐40/Int IC – albeit with a somewhat weaker equatorial zonal wind amplitude in the lower stratosphere – but are incorrect in ERA‐20C IC, indicating that the QBO is responsible for the additional NAO hindcast skill; this is despite the model exhibiting a relatively weak teleconnection between the QBO and NAO. The influence of the QBO is further demonstrated by regressing out the QBO influence from each of the hindcast experiments, after which the difference in NAO hindcast skill between the experiments is negligible. Whilst ERA‐40/Int IC demonstrates a more skilful NAO hindcast, it appears to have a relatively weak predictable signal; this is the so‐called “signal‐to‐noise paradox” identified in previous studies. Diagnostically amplifying the (weak) QBO–NAO teleconnection increases the ensemble‐mean NAO signal with negligible impact on the NAO hindcast skill, after which the signal‐to‐noise problem seemingly disappears.

The 10–30-day oscillation of winter zonal wind in the entrance region of the East Asian subtropical jet and its relationship with precipitation in southern China

Using ECMWF ERA-Interim 6-h reanalysis data, zonal wind intra-seasonal oscillations (ISOs) in the entrance region of the East Asian subtropical westerly jet (EASWJ) in winter from 1979/1980 to 2012/2013 are studied. The results first show that there is an area with large ISO strength in the northwest of the EASWJ; in the key region, zonal wind has a dominant period of 10–30 days. The composite analysis reveals that zonal wind at 200 hPa in this key region has 10–30-day oscillation characteristics. On the 10–30-day time scale, the center of zonal wind anomaly moves eastward. The propagation of zonal wind oscillation relates to temperature tendencies at different latitudes. The remarkable increase (or decrease) in zonal wind in the key region is mostly determined by temperature anomalies to the north. The 10–30-day filtered temperature advection to the north of the key region leads to either a decrease or an increase in temperature; on the other hand, temperature variations south of the key region have trends opposite of the northern trends, which changes the temperature gradient. On the 10–30-day time scale, zonal wind anomalies are associated with precipitation in southern China. When there are easterly wind anomalies over the key region, precipitation occurs over the Yangtze River basin and its south. Diabatic heating during precipitation corresponds with warming to the south of the key region, which combines with the temperature advection to weaken the easterly wind and strengths the westerly wind. Then, the intra-seasonal precipitation moves to southwest China with warm advection and the enhanced westerly wind, which brings the positive relative vorticity advection there.

Stratospheric Dynamical Response and Ozone Feedbacks in the Presence of SO2 Injections

AbstractInjections of sulfur dioxide into the stratosphere are among several proposed methods of solar radiation management. Such injections could cool the Earth's climate. However, they would significantly alter the dynamics of the stratosphere. We explore here the stratospheric dynamical response to sulfur dioxide injections ∼5 km above the tropopause at multiple latitudes (equator, 15°S, 15°N, 30°S and 30°N) using a fully coupled Earth system model, Community Earth System Model, version 1, with the Whole Atmosphere Community Climate Model as its atmospheric component (CESM1(WACCM)). We find that in all simulations, the tropical lower stratosphere warms primarily between 30°S and 30°N, regardless of injection latitude. The quasi‐biennial oscillation (QBO) of the tropical zonal wind is altered by the various sulfur dioxide injections. In a simulation with a 12 Tg yr−1 equatorial injection, and with fully interactive chemistry, the QBO period lengthens to ∼3.5 years but never completely disappears. However, in a simulation with specified (or noninteractive) chemical fields, including O3 and prescribed aerosols taken from the interactive simulation, the oscillation is virtually lost. In addition, we find that geoengineering does not always lengthen the QBO. We further demonstrate that the QBO period changes from 24 to 12–17 months in simulations with sulfur dioxide injections placed poleward of the equator. Our study points to the importance of understanding and verifying of the complex interactions between aerosols, atmospheric dynamics, and atmospheric chemistry as well as understanding the effects of sulfur dioxide injections placed away from the Equator on the QBO.

Origin of the 2016 QBO Disruption and Its Relationship to Extreme El Niño Events

AbstractThe descent of the westerly phase of the quasi‐biennial oscillation (QBO) in equatorial stratospheric zonal wind was interrupted by the development of easterlies near 40 hPa (~23 km altitude) in early 2016. We use tropical meteorological analyses of wind and temperature to describe in detail the special circumstances by which equatorward‐propagating planetary waves produced this unprecedented disruption in the QBO. Our findings show that the subtropical easterly jet in the winter lower stratosphere during the 2015–2016 winter was anomalously weak owing to (1) the timing of the QBO relative to the annual cycle and (2) an extreme El Niño event. The weak jet allowed an unusually large flux of westward momentum to propagate from the extratropical Northern Hemisphere to the equator near the 40 hPa level. Consequently, the QBO westerlies at that level experienced sustained easterly acceleration from extratropical wave breaking, leading to the observed wind reversal.

Downward Influence of QBO-Like Oscillation on Moist Convection in a Two-Dimensional Minimal Model Framework

Abstract The influence of the quasi-biennial oscillation (QBO)-like oscillation on moist convection is examined using the two-dimensional minimal model framework of Yoden et al. with two series of parameter sweep experiments: model-top experiments with varying model height and low-level nudging experiments with reduced zonal-mean zonal wind toward zero from the surface to a certain level. The QBO-like oscillation in the mean zonal wind is a robust feature obtained in all the experiments, including low-top cases in which only the tropospheric portion is retained. The zonal-mean precipitation is modulated with a half period of the mean zonal wind oscillation in the model-top experiments, and a positive correlation exists between the precipitation intensity and the vertical shear of the mean zonal wind near the surface. The precipitation modulation is weakened with a nudging of the low-level mean zonal wind but appears again in the cases with the low-level nudging in the middle and lower troposphere. There is a negative correlation between the precipitation intensity and the vertical shear of the mean zonal wind in the upper troposphere. These results suggest that the QBO-like oscillation modulates the moist convection via two mechanisms related to the vertical shear. Large values of the shear near the surface enhance the longevity and intensity of the moist convective systems by separating the updraft and downdraft. On the other hand, large values of shear near the cloud top tend to disrupt the convective structure and lead to weakening moist convection, although this mechanism seems to be secondary.

Evidence of Tropospheric 90 Day Oscillations in the Thermosphere

AbstractIn the last decade evidence demonstrated that terrestrial weather greatly impacts the dynamics and mean state of the thermosphere via small‐scale gravity waves and global‐scale solar tidal propagation and dissipation effects. While observations have shown significant intraseasonal variability in the upper mesospheric mean winds, relatively little is known about this variability at satellite altitudes (∼250–400 km). Using cross‐track wind measurements from the Challenging Minisatellite Payload and Gravity field and steady‐state Ocean Circulation Explorer satellites, winds from a Modern‐Era Retrospective Analysis for Research and Applications/Thermosphere‐Ionosphere‐Mesosphere‐Electrodynamics General Circulation Model simulation, and outgoing longwave radiation data, we demonstrate the existence of a prominent and global‐scale 90 day oscillation in the thermospheric zonal mean winds and in the diurnal eastward propagating tide with zonal wave number 3 (DE3) during 2009–2010 and present evidence of its connection to variability in tropospheric convective activity. This study suggests that strong coupling between the troposphere and the thermosphere occurs on intraseasonal timescales.

Modeling study of the ionospheric responses to the quasi-biennial oscillations of the sun and stratosphere

The Quasi-biennial Oscillation (QBO) is a persistent oscillation in the zonal mean zonal winds of the low latitude middle atmosphere that is driven by breaking planetary and gravity waves with a period near two years. The atmospheric tides that dominate the dynamics of the mesosphere and lower thermosphere region (MLT, between heights of 70–120 km) are excited in the troposphere and stratosphere, and propagate through QBO-modulated zonal mean zonal wind fields. This allows the MLT tidal response to also be modulated by the QBO, with implications for ionospheric/thermospheric variability. Interannual oscillations in solar radiation can also directly drive the variations in the ionosphere with similar periodicities through the photoionization. Many studies have observed the connection between the solar activity and QBO signal in ionospheric features such as total electron content (TEC).In this research, we develop an empirical model to isolate stratospheric QBO-related tidal variability in the MLT diurnal and semidiurnal tides using values from assimilated TIMED satellite data. Migrating tidal fields corresponding to stratospheric QBO eastward and westward phases, as well as with the quasi-biennial variations in solar activity isolated by the Multi-dimensional Ensemble Empirical Mode Decomposition (MEEMD) analysis from Hilbert-Huang Transform (HHT), are then used to drive the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM).The numerical experiment results indicate that the ionospheric QBO is mainly driven by the solar quasi-biennial variations during the solar maximum, since the solar quasi-biennial variation amplitude is directly proportionate to the solar cycle. The ionospheric QBO in the model is sensitive to both the stratospheric QBO and solar quasi-biennial variations during the solar minimum, with solar effects still playing a stronger role.

The Semiannual Oscillation of the Tropical Zonal Wind in the Middle Atmosphere Derived from Satellite Geopotential Height Retrievals

Abstract The dominant mode of seasonal variability in the global tropical upper-stratosphere and mesosphere zonal wind is the semiannual oscillation (SAO). However, it is notoriously difficult to measure winds at these heights from satellite or ground-based remote sensing. Here, the balance wind relationship is used to derive monthly and zonally averaged zonal winds in the tropics from satellite retrievals of geopotential height. Data from the Aura Microwave Limb Sounder (MLS) cover about 12.5 yr, and those from the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) cover almost 15 yr. The derived winds agree with direct wind observations below 10 hPa and above 80 km; there are no direct wind observations for validation in the intervening layers of the middle atmosphere. The derived winds show the following prominent peaks associated with the SAO: easterly maxima near the solstices at 1.0 hPa, westerly maxima near the equinoxes at 0.1 hPa, and easterly maxima near the equinoxes at 0.01 hPa. The magnitudes of these three wind maxima are stronger during the first cycle (January at 1.0 hPa and March at 0.1 and 0.01 hPa). The month and pressure level of the wind maxima shift depending on the phase of the quasi-biennial oscillation (QBO) at 10 hPa. During easterly QBO, the westerly maxima are shifted upward, are about 10 m s−1 stronger, and occur approximately 1 month later than those during the westerly QBO phase.

On the association between the recent episode of the quasi-biennial oscillation and the strong El Niño event

Since February 2016, the equatorial quasi-biennial oscillation (QBO) in zonal wind of the lower stratosphere exhibited anomalous behavior. In more detail, it broke down from its typical pattern and the eastward stratospheric winds unexpectedly reversed to a westward direction. We herewith attempt to detect whether this unprecedented event could be considered as a result of plausible long-range correlations in the QBO temporal evolution. The analyses performed using all the available QBO data sets showed that such an interpretation could not be inferred, because the temporal evolution of the equatorial zonal wind in the lower stratosphere does not exhibit power-law behavior. Further, the natural time analysis of the QBO data indicates precursory behavior before the maximization of the zonal wind velocity and that the recent strong El Nino event might be related with the aforementioned unprecedented behavior.

Tropical temperature variability and Kelvin-wave activity in the UTLS from GPS RO measurements

Abstract. Tropical temperature variability over 10–30 km and associated Kelvin-wave activity are investigated using GPS radio occultation (RO) data from January 2002 to December 2014. RO data are a powerful tool for quantifying tropical temperature oscillations with short vertical wavelengths due to their high vertical resolution and high accuracy and precision. Gridded temperatures from GPS RO show the strongest variability in the tropical tropopause region (on average 3 K2). Large-scale zonal variability is dominated by transient sub-seasonal waves (2 K2), and about half of sub-seasonal variance is explained by eastward-traveling Kelvin waves with periods of 4 to 30 days (1 K2). Quasi-stationary waves associated with the annual cycle and interannual variability contribute about a third (1 K2) to total resolved zonal variance. Sub-seasonal waves, including Kelvin waves, are highly transient in time. Above 20 km, Kelvin waves are strongly modulated by the quasi-biennial oscillation (QBO) in stratospheric zonal winds, with enhanced wave activity during the westerly shear phase of the QBO. In the tropical tropopause region, however, peaks of Kelvin-wave activity are irregularly distributed in time. Several peaks coincide with maxima of zonal variance in tropospheric deep convection, but other episodes are not evidently related. Further investigations of convective forcing and atmospheric background conditions are needed to better understand variability near the tropopause.

Correlations of latitudinal dynamics of atmospheric moisture content with quasi-biennial oscillations of zonal wind in the equatorial stratosphere and solar activity over the north-east of Eurasia during 1979-2015

Correlations of latitudinal dynamics of atmospheric moisture content with quasi-biennial oscillations of zonal wind in the equatorial stratosphere and solar activity over the north-east of Eurasia during 1979-2015