The transmission of three-dimensional anelastic internal gravity wave packets incident upon a retrograde background jet flow are examined through fully nonlinear numerical simulations. The background winds are chosen to be representative of the eastward and westward flows of the Quasi-Biennial Oscillation (QBO) in the equatorial stratosphere. Transmission, which is quantified by the relative pseudomomentum of waves passing above the jet, is found to be smaller for incident waves with larger initial frequency. Due to anelastic effects, the amplitude of the transmitted wave packets tends to grow exponentially, ultimately inducing a local mean flow that acts to drive the waves to overturn and break turbulently. The results are compared with previous studies that predicted transmission of small amplitude wave packets, and implications are discussed for the influence of wave transmission across the QBO.

Abstract Winter precipitation forecasting at sufficient lead times has several benefits, including aiding water allocation decisions and supporting individual water users’ decision-making. This study evaluates the performance of ensemble-mean cool-season (December through March) precipitation forecasts from individual models within the North American Multi-Model Ensemble (NMME) over the Colorado River basin and California’s Sacramento–San Joaquin–Tulare basins (hereafter referred to as the SST). These ensemble-mean forecasts are compared to a newly developed statistical forecasting model, using the rain-gauge-based Parameter-elevation Regressions on Independent Slopes Model (PRISM) as the reference product. While NMME models effectively capture the spatial pattern of mean precipitation, they struggle to predict year-to-year variability and extremes. Forecast skill is higher in the Colorado basin than in the SST Basin. Anomaly correlations between ensemble-mean NMME forecasts and observations vary by model and basin, with GEM5-NEMO and GFDL-SPEAR showing relatively higher skill. Performance in forecasting droughts and wet/dry years remains inconsistent across models, with most models missing key events such as the 2023 and 2017 wet years and the 2022 drought. Simple statistical models using key atmospheric–oceanic predictors outperformed the more complex ensemble-mean NMME dynamical models in both basins. The most effective predictors were the Oceanic Niño Index, Tropical South Atlantic sea surface temperatures, and the Quasi-Biennial Oscillation for the SST Basin, and the North Atlantic Oscillation and Tropical North Atlantic sea surface temperatures for the Colorado basin.

Abstract The Quasi-Biennial Oscillation (QBO) and the El Niño Southern Oscillation (ENSO) both influence the strength of the stratospheric polar vortex, with weakening of the polar vortex during the easterly QBO and El Niño. The polar vortex is also thought to weaken in response to Arctic sea-ice loss, related to an equatorward shift of the mid-latitude jet stream. However, it is unclear how these factors impact the polar vortex in combination and whether their influences are linearly additive. Here using atmospheric general circulation model experiments, we show that in our model, in the presence of Arctic sea-ice loss, the polar vortex weakens significantly during easterly QBO, but not during westerly QBO; and weakens significantly during neutral ENSO, but not during El Niño. This suggests that the polar vortex responses to sea-ice loss, QBO, and ENSO are interdependent and non-additive. This interdependence cannot be explained by the polar vortex background state, since the easterly QBO and El Niño both separately weaken the polar vortex, but have an opposite-signed influence on the response to sea-ice loss. Instead, we surmise the modulation is governed by how QBO and ENSO affect anomalous wave propagation into the stratosphere in response to sea-ice loss. At the surface, sea-ice loss enhances the Siberian High and causes cooling over Eurasia in QBO-E but not QBO-W. Both QBO-W and El Niño damp the equatorward tropospheric jet shift in response to sea-ice loss, relative to QBO-E or neutral ENSO, respectively. The existence of these non-linearities has implications for subseasonal to interannual climate prediction.

Abstract Quasi-biennial oscillations (QBOs) are shorter-term periodic signals that occur alongside the dominant 11-year solar cycle. In this study, we examine the spatial and temporal evolution of QBOs using helioseismic p-mode frequency shifts from the Global Oscillation Network Group (GONG) across solar Cycles 23 and 24 and the ascending phase of Cycle 25. By applying wavelet analysis to frequency shifts, we studied the changes in QBO periodicities to determine whether the QBO period and amplitude vary with latitude. Our results show that QBO periods exhibit a weak latitudinal dependence, with shorter and less persistent signals at low latitudes, while at higher latitudes the periods are nearly constant at ∼3 years. Cycle 24 tends to display slightly longer periods than Cycle 23, though within uncertainties. At all latitudes, QBO amplitudes increase with mode frequency, which is consistent with previous studies. Higher amplitude QBOs are found at low latitudes, reflecting the distribution of surface magnetic activity. The ratio of QBO to cycle amplitude is systematically higher in Cycle 24 than in Cycle 23, and above 20○ latitude the amplitude ratio is nearly uniform in Cycle 23 but shows modest variations in Cycle 24. A linear relation between QBO amplitude and cycle amplitude is found in both cycles, but with significantly different slopes, indicating that QBO amplitudes are not wholly governed by the solar cycle strength and are at least partially decoupled from it. Finally, we find no evidence that QBO period depends on QBO amplitude, consistent with a linear oscillation regime.

Abstract The Quasi‐Biennial Oscillation (QBO) is a dominant mode of stratospheric variability and is known to modulate the variability of the ionosphere‐thermosphere (IT) system. However, the extent of its influence on the ionosphere‐thermosphere system remains uncertain due to weak signals and confounding with similar periodicities in solar flux. In this study, we investigated QBO signatures in ionosonde derived peak electron density (NmF2), GNSS total electron content (TEC), and thermospheric composition ( O / N 2 ) from the Global Ultraviolet Imager on NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. Local empirical models are used to isolate the stratospheric QBO signature in NmF2 and TEC. Multi‐channel singular spectrum analysis is used to reveal seasonal modulation of the O/N 2 response to QBO. We found that the amplitude of non‐solar origin QBO in NmF2, TEC, and O/N 2 reaches up to 4% and exhibits an out‐of‐phase relation with stratospheric QBO phase at 30 hPa (QBO30). The TEC QBO signal shows strong regional variability, peaking over Europe. The O/N 2 QBO signal shows clear seasonality with maximum correlation with QBO30 around the equinoxes. The NmF2 response to stratospheric QBO is enhanced at most stations during the September equinox. The QBO signal in O / N 2 at different latitudes shows maximum correlation with the stratospheric QBO at different pressure levels. Overall, the global reduction in NmF2, TEC, and O / N 2 during the eastward QBO phase, along with their seasonal structure, is consistent with enhanced mixing driven by migrating diurnal tide. However, the regional structure in the TEC response implies additional mechanisms with varying spatial influence and vertical extent.

Abstract Based on the Grid‐point Atmospheric Model of the Institute of Atmospheric Physics LASG version 3 (GAMIL3) with 2° horizontal resolution, the whole‐atmospheric model named W‐GAMIL1.0, with a high top (approximately 0.01 hPa) and 137 vertical levels, was developed through modifying the standard stratification profile and interpolation method, incorporating non‐orographic gravity wave (NGW) parameterization schemes, and adjusting the convective processes for strong variability. Twenty‐six‐year Atmospheric Model Intercomparison Project integrations indicated that W‐GAMIL1.0 markedly improves the stratospheric dynamical variables owing to its high model lid and increased vertical resolution, including reductions in cold biases and dry biases in the tropic. When the frequency and accumulation of convective precipitation are increased through changing the convection scheme, the Madden–Julian Oscillation (MJO) convection, Quasi‐Biennial Oscillation (QBO) westerlies and downward propagation are strengthened substantially. The mean period, height of maximum amplitude, and lowest level of the QBO are also well reproduced. Under the background of strong QBO westerlies, the Semi‐Annual Oscillation (SAO) westerly and the frequency of sudden stratospheric warming events are obviously overestimated in W‐GAMIL1.0, mainly because of (convective) gravity wave forcing. However, the eastward propagation of MJO convection, the vertical and latitudinal extents as well as the amplitude and descent rate of the QBO, and the SAO easterly are all underestimated, indicating the importance of compatibility between the vertical and horizontal resolutions, and between the convective process and convective NGW process in the development of a whole‐atmospheric model.

The joint influence of the Madden Julian Oscillation and Quasi Biennial Oscillation on the long rains over East Africa

Abstract An intermediate complexity general circulation model is used to isolate the effect of vertical resolution and gravity wave parameterization on the simulated monthly quasi‐biennial oscillation (QBO)‐tropical precipitation linkage. For low vertical resolution, the model is able to simulate QBO in the lowermost stratosphere, and its impact on the tropical upper troposphere‐lower stratosphere (UTLS) and precipitation, only after optimizing the gravity wave parameterization. For increased vertical resolution, the impact of the QBO on UTLS static stability is stronger. However, the tropical precipitation response is qualitatively different from that at low resolution. The precipitation response contains a substantial zonal and meridional structure that differs qualitatively between low and high vertical resolution. Two factors appear to explain this difference: the meridional width of the QBO, and the presence of a warmpool in the West Pacific. These results have implications for the ability of comprehensive models to simulate a tropical response to the QBO.

Abstract This study investigates the interdecadal stability of the relationship between the Quasi-Biennial Oscillation (QBO) and East Asian peak summer (July–August) precipitation using long-term observational and reanalysis datasets from 1959 to 2020. Results show a significant strengthening of the June QBO’s influence on regional precipitation over East Asia after the 1990s. Before the 1990s, the QBO index at 30 hPa showed weak correlations with peak summer precipitation. However, after the 1990s, it exhibits significantly positive correlations with precipitation over South China (SC) and negative correlations over the Yangtze–Huaihe River Basin (YHRB), including associated shifts in precipitation extremes. This change is primarily linked to changes in the vertical structure of the QBO. After the 1990s, QBO-related westerly anomalies extended deeper into the troposphere, facilitated by a transition from northerly to southerly wind anomalies in the lower stratosphere. These structural changes promoted enhanced downward propagation of zonal wind anomalies, leading to subtropical cyclonic anomalies and increased vorticity. The Rossby wave responses and wave activity flux divergence/convergence produced a robust zonal wind dipole over East Asia, reinforcing moisture transport and vertical motion. These circulation changes gave rise to a meridional dipole in precipitation centered near 30°N, with increased precipitation over the SC and decreased precipitation over the YHRB. The findings highlight a significant shift in the QBO–precipitation relationship, suggesting enhanced predictive potential of the QBO for East Asian summer rainfall in recent decades.

Abstract The quasi‐biennial oscillation (QBO) is a fundamental mode of atmospheric variability and a textbook example of wave‐mean flow interactions. While its general theory has been established about 50 years ago by the seminal works of Holton, Lindzen and Plumb (HLP), it remains an unsettled problem of geophysical fluid dynamics and a challenge for atmospheric general circulation models (GCM). In this study, we investigate wave‐mean flow interaction and QBO‐like dynamics in a new idealized 2D (altitude‐longitude) numerical setup based on the Weather Research and Forecasting (WRF) model. The model is designed to reproduce in 2D the minimal 1D model proposed by HLP. Namely, two gravity waves of opposite phase speed are explicitly resolved; they are forced through periodic heating in the lower part of the domain, and propagate vertically and dissipate through Newtonian cooling and viscous damping. In this configuration, we obtain a periodic wind reversal similar to the QBO. We characterize the evolution of the wave field and momentum budget of the mean flow in both our 2D and the 1D HLP framework. Then, the sensitivity of the flow to model parameters is assessed and compared with theoretical predictions as well as the original HLP model. This exercise highlights the impact of explicit wave forcing on wave‐mean flow interactions as well as the role of forcing amplitude and vertical viscosity in shaping the flow. Implications for QBO representations and predictions in a model hierarchy ranging from simple models to GCMs are discussed.

The article presents the results of a comprehensive analysis of the agroclimatic conditions in the Penza Region for the period 2019–2024 and their impact on spring wheat yield. Based on data from the Russian Hydrometeorological Center and the Volga Department for Hydrometeorology and Environmental Monitoring, the main limiting factors of grain production have been identified. Using correlation and regression analysis, a statistically significant dependence of yield on moisture availability during critical phases of plant development has been established. For the first time in the region, a differentiated system of adaptation measures is proposed, taking into account the quasi-biennial oscillation and zonal characteristics. The research results have practical significance for stabilizing grain production under changing climatic conditions.

The main objective of this work is to characterize Sudden Stratospheric Warming (SSW) conditions and their impact on local weather forecasting and climate change, using SSW definition criteria. The SSWs strongly affect Arctic vortex structure and midlatitude weather conditions. This work evaluates the frequency, amplitude, and dynamical–thermal characteristics of SSWs under historical and Representative Concentration Pathway (RCP) 4.5 scenarios, focusing on stratospheric air temperature (Ts) and zonal wind speed (Uh) at the 10° N and 60° N latitudes. The fifth-generation ECMWF atmospheric reanalysis (ERA5) is employed as the reference dataset. Simulations of five Coupled Model Intercomparison Project Phase 5 (CMIP5) models, represented by M1 to M5, are analyzed. The primary group of models included 1) the Australian Community Climate and Earth-System Simulator, version 1.3 (ACCESS1-3, M1), 2) the Hadley Center Global Environmental Model, version 2—Carbon Cycle (HadGEM2-CC, M2), and 3) the Max Planck Institute Earth System Model—Medium Resolution (MPI-ESM-MR, M3). The analysis period covers SSW events related to the Quasi-Biennial Oscillation (QBO) in the Northern Hemisphere (NH) from 1980 to 2100. The key findings indicate that while M1, M2, and M3 simulate SSW occurrence correctly for the 21st century, they exhibit significant systematic deficiencies in capturing the structural dynamics of SSW events. Specifically, the M1, M2, and M3 models underestimate the polar stratospheric temperature amplitude (Tamp) by approximately 75–80% and zonal wind amplitude (Uamp) by more than 60% compared to the ERA5 analysis. Furthermore, ERA5 exhibits a strong negative correlation (R ≈ −0.8) between Uh and Ts that is not estimated accurately using the present models. The importance of the horizontal resolution of the models and wave–mean flow interactions in determining SSW intensity and occurrence is also found to be a critical metric. Results suggest that SSW definition criteria affect Arctic and midlatitude weather system prediction at a rate of 61–82%. It is concluded that the primary configurations of CMIP5 models for accurately capturing the dynamical structure and evolution of QBO–SSW interactions are needed, and that they affect future projections of SSW events.

The Earth’s quasi-biennial oscillation (QBO) is a natural example of wave–mean flow interaction and corresponds to the alternating directions of winds in the equatorial stratosphere. It is due to internal gravity waves (IGWs) generated in the underlying convective troposphere. In stars, a similar situation is predicted to occur, with the interaction of a stably stratified radiative zone and a convective zone. In this context, we investigate the dynamics of this reversing mean flow by modelling a stably stratified envelope and a convectively unstable core in polar geometry. Here, the coupling between the two zones is achieved self-consistently, and IGWs generated through convection lead to the formation of a reversing azimuthal mean flow in the upper layer. We characterise the mean flow oscillations by their periods, velocity amplitudes and regularity. Despite a continuous broad spectrum of IGWs, our work shows good qualitative agreement with the monochromatic model of Plumb & McEwan (1978, J. Atmos. Sci. vol. 35, no. 10, pp. 1827–1839). While the latter was originally developed in the context of the Earth’s QBO, then our study could prove relevant for its stellar counterpart in massive stars, which host convective cores and radiative envelopes.

Abstract Zonal asymmetry in the amplitude of the Quasi-Biennial Oscillation (QBO) is investigated using JRA-55 reanalysis data and in-situ IGRA radiosonde observations. In addition to the previously reported asymmetry near 10 hPa, significant longitudinal variation with the largest amplitudes over the western and central Pacific is found around 70 hPa. Unlike the dominant wavenumber-1 pattern near 10 hPa, the structure at 70 hPa exhibits more localized variations. Longitudinal differences in the QBO zonal wind at 70 hPa reach up to 30%, indicating that the descent of the QBO into the lower stratosphere and upper troposphere exhibits pronounced longitudinal variation. The asymmetry results were confirmed in five additional reanalysis datasets. Similar zonal variation of QBO amplitudes is also identified in radiosonde observations and in both CMIP6 and QBOi models that explicitly simulate the QBO. These results demonstrate that the longitudinal structure of the 70-hPa QBO amplitude is a robust feature across observations, reanalyses, and climate models.

Abstract. This study uses an ensemble of climate model experiments coordinated by the Quasi-Biennial Oscillation initiative (QBOi) to analyze the Madden-Julian Oscillation (MJO) in the presence of either perpetual El Niño or La Niña sea surface temperatures during boreal winter. In addition to the prescribed El Niño Southern Oscillation (ENSO) conditions, the nine models internally generate QBOs, meaning each may influence the MJO. Objectives of our analyses are to assess the response of the MJO to strong idealized ENSO forcing and look for evidence of a QBO influence on the MJO in a multi-model context. The diagnostics used include wavenumber-frequency spectra of tropical convective and dynamical fields, measures of MJO lifetime, an evaluation of MJO diversity and visualization of MJO vertical structure, as well as an assessment of QBO morphology and the QBO's impact on tropical convection. Kelvin wave spectral power increases in the El Niño simulations whereas equatorial Rossby waves power is stronger in the La Niña simulations. All models simulate faster MJO propagation under El Niño conditions. This change in speed is corroborated by the MJO diversity analysis, which reveals that models better reproduce the observed “fast propagating” and “standing” MJO archetypes given perpetual El Niño and La Niña, respectively. Regardless of ENSO, QBO descent into the lower stratosphere is underestimated and we detect little QBO influence on tropical tropopause stability and MJO activity. With little influence from the QBO on the MJO activity in these runs, we can be confident that the aforementioned changes in the MJO indeed arise from the different ENSO boundary conditions.

Abstract The long-term occurrence of mesospheric inversion layers (MILs) was analyzed using 22 years (2002–23) of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature data. The two types of MILs considered are those caused by dissipating waves and those caused by nondissipating waves. We examined MIL occurrence near-globally, monthly, and latitudinally, applying multiple linear regression (MLR) to assess trends and responses to El Niño–Southern Oscillation (ENSO), quasi-biennial oscillation (QBO), and solar flux ( F 10.7cm ). MIL parameters (top/base heights and temperatures, height/temperature variations) exhibit clear hemispherical asymmetry. In general, MIL occurrences peak during equinoxes and decline during solstices. Latitudinally, tropical regions (30°N–30°S) show the highest MIL occurrences during equinoxes and the lowest ML occurrences during solstices. In midlatitudes and polar regions (30°–83°N/S), MILs peak in autumn and winter, with a minimum in spring and summer. Periodicities in MIL occurrences vary near-globally and by latitude. The tropics feature not only the smallest mean thickness variation (∼0.61 km) but also the largest mean temperature amplitude variation (∼23.72 K). The latitudinal patterns may reflect seasonal variations in dynamics that have a stronger influence on temperature inversions than on the vertical distributions in the mesosphere. Over 22 years, the analysis revealed a near-global MIL occurrence ratio increase of approximately 0.055% ± 0.016% yr −1 , with the 11-yr solar cycle exerting significant control. The observed negative correlation with ENSO and positive correlation with QBO likely reflect their influence on atmospheric wave propagation and circulation, which indirectly modulates MIL formation.

The stratospheric quasi-biennial oscillation (QBO) is a key modulator of interannual variability in global weather and climate. Over recent decades, the amplitude of the lower-stratospheric QBO has weakened, and in recent years the QBO has experienced unprecedented disruptions. However, the longer-term evolution of the QBO and its impact on tropospheric circulation remain uncertain. Here, based on CMIP6 models with extended projections beyond 2100 and targeted sensitivity experiments, we show that under ongoing global warming, the QBO exhibits a progressively weaker amplitude and shorter period, eventually risking complete disappearance. This is projected to reduce the predictability of 2-3-year climate forecasts in the troposphere. The weakening of the QBO amplitude arises from enhanced tropical upwelling, whereas the shortening of its period results from the combined influence of strengthened upwelling and intensified wave activity. The potential disappearance of the QBO poses new challenges for climate change under high emission.

Abstract. The quasi-biennial oscillation (QBO) is the main mode of variability in the tropical stratosphere, influencing the predictability of other regions in the atmosphere through its teleconnections to the stratospheric polar vortices and coupling to surface tropical and extratropical variability. However, climate and forecasting models consistently underestimate QBO amplitudes in the lower stratosphere, likely contributing to their failure to simulate these teleconnections. One underexplored contributor to model biases is missing representation of ozone-radiative feedbacks, which enhance temperature variability in the lower stratosphere, particularly at periods at and greater than the QBO (>28 months). While previous studies suggest that ozone-radiative feedbacks can impact QBO periods, amplitudes and the associated secondary circulation in the lower stratosphere, the reported impacts differ widely among models and are hard to interpret due to differences in methodology. To this end, here we propose a coordinated experimental protocol – held joint between the Atmospheric Processes and their Role in Climate (APARC) Quasi-Biennial Oscillation Initiative (QBOi) and Chemistry Climate Modeling Initiative (CCMI) activities – which is aimed at assessing the coupling between stratospheric ozone, temperature and the circulation. We use the proposed experiments to define the ozone feedback on the QBO in both present-day and idealized (abrupt quadrupling of carbon dioxide) climates. While primary focus is on the QBO, the proposed protocol also enables analysis of other aspects of ozone-radiative-dynamical coupling in the atmosphere, including impacts on the Brewer-Dobson Circulation and tropospheric eddy-driven jet responses to future climate change. Here we document the scientific rationale and design of the QUOCA Phase 1 experiments, summarize the data request, and give a brief overview of participating models. Preliminary results using the NASA Goddard Institute for Space Studies E2-2 climate model are used to illustrate sensitivities to certain methodological choices.

Abstract. Polar stratospheric clouds (PSCs) play a critical role in stratospheric ozone depletion. Previous studies have shown that the quasi-biennial oscillation (QBO) influences the Arctic stratospheric polar vortex and ozone, yet few studies have thoroughly analyzed the impact of the QBO on Arctic PSC occurrence. This study examines this impact using CALIPSO observations from 2006 to 2021 and SLIMCAT simulations from 1979 to 2022. The results show that the winter PSC coverage area is significantly larger during the westerly QBO (WQBO) phase than during the easterly QBO (EQBO) phase, with a zonal asymmetry in PSC occurrence frequency anomalies. The QBO influences the temperature, water vapour (H2O), and nitric acid (HNO3) in the Arctic stratosphere, which are key factors affecting PSC formation. During the WQBO phase, Arctic stratospheric temperatures show negative anomalies, with the centre of this anomaly biased towards North America. In addition, H2O shows positive anomalies in the Arctic lower stratosphere, mainly due to the stronger polar vortex preventing the transport of high-moisture air at high latitudes to mid-latitudes, causing H2O to accumulate inside the polar vortex. HNO3 shows negative anomalies, primarily caused by denitrification through nitric acid trihydrate (NAT) sedimentation. Sensitivity analyses further indicate that QBO-induced temperature anomalies are the dominant driver of PSC variability, while the direct effect of H2O anomalies on PSCs is relatively small. The reduction of HNO3 mainly affects PSCs in February and March. This work implies that future changes in the QBO may influence ozone by affecting PSCs.

Abstract The traditional view posits that vertically propagating mixed Rossby‐gravity (MRG) waves generated in the troposphere partly contribute to driving the Quasi‐Biennial Oscillation (QBO) in the tropical lower stratosphere. However, recent studies suggest that MRG waves may be generated locally within the QBO region, potentially via barotropic instability. This study supports this alternative mechanism by showing that the tropical zonal mean flow at 30 hPa in ERA5 reanalysis satisfies the necessary conditions for barotropic instability approximately in 60% of cases, increasing to about 80% during the westerly QBO phase twice as frequent as during the easterly phase. Additionally, the MRG wave kinetic energy spectra at 30 hPa show increased energy at zonal wavenumbers in the westerly QBO phase compared to the easterly phase. The linear analysis within the QBO region reveals that MRG waves contribute between 4 and 14 times more to the total energy of the unstable modes during the westerly QBO phase, for zonal wavenumbers . Idealized numerical simulations of the QBO flow demonstrate that the enhanced MRG wave spectral power at synoptic and sub‐synoptic scales during the westerly QBO phase results from barotropic instability development. Together, these results suggest that the stronger MRG wave generation observed during the westerly QBO arises from both the greater frequency of unstable flow conditions and the higher MRG wave energy in the unstable modes.