Abstract North China frequently experiences devastating extreme precipitation events (EPEs). Upstream spatiotemporal propagation characteristics of EPEs can provide useful precursors for forecasting North China EPEs but remains poorly understood. Using climate network analysis, two dominant EPEs propagation pathways, that is, a northwestern pathway from West Siberian Plain (6‐day lead) and a southwestern pathway from Tibetan Plateau (TP) (3‐day lead), are identified during the warm season. The northwestern pathway is driven by an eastward‐propagating mid‐latitude wave train coupled with Arctic cyclone. The cyclone in the wave train drives the southeastward‐propagating EPEs, and when it merges with the Arctic cyclone, its downstream anticyclone is enhanced, ultimately inducing North China EPEs. The southwestern pathway stems from quasi‐stationary waves coupled with Arctic anticyclone. Interactions between anticyclone in the wave train and Arctic anticyclone generate a TP cyclone, whose intensification and eastward expansion propel EPEs northeastward and strengthen the Northeast Asian anticyclone, ultimately causing North China EPEs.

Half-metallic multifunctionality induced by electron doping in twisted bilayer perovskite with polar vortex patterns

Context . Jupiter’s polar upper troposphere and stratosphere host a persistent cold vortex poleward of 65°N, but its detailed structure and dynamics have remained difficult to resolve. Aims . The goal is to characterize the thermal structure and dynamics of the polar vortex using new and complementary remote sensing techniques. Methods . We used a combination of high-resolution vertical profiles derived from Juno’s recent radio occultation measurements and mid-infrared imaging from the VLT/VISIR instrument. The former provided direct retrievals of temperature and density near and within the vortex, while VISIR imaging revealed spatial thermal contrasts across the region. Results . Our analysis confirms the presence of a steep meridional temperature jump at 65°N, of about 7±1 K at 100 mbar, which is consistent with a strong vertical wind shear and a prograde polar stratospheric jet reaching up to 80 ms −1 at the 10 mbar level. We find the atmosphere to be thermally stable above 0.55 bar, reaching a Brunt-Väisälä frequency of 0.025 s −1 in the mid-stratosphere. Thermal contrasts observed in the infrared data align with the vertical structures inferred from radio occultations, which validates the presence and extent of the cold vortex. Conclusions . These findings offer a quantitative analysis of the thermal structure and the dynamical behavior of Jupiter’s polar atmosphere and demonstrate the diagnostic power of combining radio occultation and thermal infrared techniques in planetary atmospheric studies.

The distinct polar vortex dynamics observed on Jupiter and Saturn may provide insights into their interiors. In this study, we examine how the number and structure of polar vortices vary with forcing strength, dissipation rate, and interior stratification using a 1.5-layer quasi-geostrophic model. This simplified setup enables a broad exploration of the parameter space, revealing that vortex characteristics are determined by the sequence in which three key length scales-the deformation radius [Formula: see text], the zonostrophic scale [Formula: see text], and the dissipative scale [Formula: see text]-are encountered as energy cascades from small to large scales. Four distinct vortex patterns are identified, including a vortex crystal resembling Jupiter's polar vortices and a single-vortex state akin to that of Saturn. The conditions under which these patterns emerge provide constraints on the stratification of Jupiter and Saturn.

Abstract. To predict the future state of the Earth system on multiyear timescales, it is crucial to understand the response to changing external radiative forcing (CO2 and Ozone). Analyzing the Northern Hemisphere (NH) winter stratospheric polar vortex temperature, we found a general temperature decrease in the reanalysis data (1982–2020), the expected trend with increasing CO2, except for a sharp warming during the period 1992–2000. Results from 1° GEOS-MITgcm coupled general circulation model simulations of past decades show a similar increase in the NH polar stratospheric temperature during 1992–2000 and a decrease during 2000–2020. To isolate the influence of external forcing, we conducted a series of 30-year-long “perpetual” time-slice experiments in which the external forcing for a particular year is held fixed at its values for 1992, 2000, and 2020. Each simulated year of these perpetual experiments is forced with the CO2, Ozone, anthropogenic aerosol emissions, and trace gases of that year, but none of the simulations include any explosive volcanic forcing. The increasing and then decreasing temperature trend is also manifest in the CMIP6 historical simulations performed with models that include a well-resolved stratosphere. The configuration of the perpetual experiments rules out a direct response to volcanic emissions or a change in the phase of decadal modes of variability as explanations for the warming rather than the expected cooling behavior. Analysis of the temperature budget showed (only significant terms are discussed) that the polar stratospheric temperature behavior is dictated by meridional eddy transport of heat resulting from changes in CO2 and Ozone over the past decades.

Are stratospheric polar vortex disruptions what they seem? An alternative metric excludes tropospheric influences

Abstract In mid‐winter 2024, extraordinary stratospheric warming occurred over the sub‐Antarctic region with two distinctive warming maxima in mid‐July to early August, followed by record negative anomalies in the southern annular mode (SAM) during late July to early August. However, the causality between these stratospheric and tropospheric extreme events remains unclear due to the rarity of such downward coupling during Southern Hemisphere (SH) winter—previous Antarctic stratospheric warmings and their associated downward coupling have largely occurred during SH spring. Here we provide insights into the dynamics and climate impacts of wintertime Antarctic vortex variability during 1979–2023 and compare the climatological behavior of wintertime SH stratosphere‐troposphere coupling with that observed during mid‐winter 2024. During 1979–2023, compared to the springtime stratospheric polar vortex variability in the SH, which is characterized by variations in vortex strength and breakdown timing and its robust signature in surface climate, wintertime variability in the SH stratospheric circulation is marked by expansion and contraction of the vortex with generally weak linkages to surface circulation. The 2024 mid‐winter event mirrored many historical features of wintertime variability at stratospheric levels but had a much stronger signature in surface climate. It was unique with a record contraction of the vortex accompanied by record increases in polar stratospheric temperatures for July. These unusual stratospheric conditions atypically led to substantially higher‐than‐normal Antarctic ozone concentrations in July and August, delaying the development of the ozone hole, and record negative values in the SAM and extraordinary warmth over the Antarctic continent in early August 2024.

Abstract The mechanism driving the lower thermospheric meridional circulation is analyzed using the high‐resolution Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension (WACCM‐X). In the winter lower thermosphere, eastward forcing is dominant around z =120 km, consistent with equatorward circulation. Following previous studies, the vertical flux of the zonal momentum is examined for small‐scale waves with zonal scales smaller than 2,000 km through the depth of the middle atmosphere. Wave decomposition analysis reveals that eastward waves with a wide range of phase speeds are generated around the polar vortex height. This result differs from the conventional understanding in gravity wave parameterizations, which states that eastward waves slower than the strong mesospheric wind cannot propagate to higher altitudes. Quasi‐stationary and westward waves are also active in the mesosphere, some of which originate in the troposphere. However, these waves more often dissipate in the upper mesosphere at critical levels and easterly shear, which results in the dominance of eastward waves in the lower thermosphere. The horizontal and temporal variations of gravity wave activity in the lower thermosphere are associated with the structure of the mesospheric jet. These results suggest a possible method for diagnosing wave generation that could improve gravity wave parameterizations. In the summer hemisphere, westward forcing is expressed by the semidiurnal tide, as well as by filtered gravity waves. Thus, the driving mechanisms of the lower thermospheric circulation are the contribution of gravity waves, mainly generated in the mesosphere and selectively filtered in the upper mesosphere, and the semidiurnal tide.

Oxide-based moiré superlattice is an emerging field for its exotic properties and abundant design freedom. However, due to the dangling bond and much stronger interlayer adhesion with the supporting substrate, fabricating twisted complex oxide is challenging, and an oxide moiré lattice with a clean interface remains elusive. Here, square moiré superlattices in twisted SrTiO3 (STO) bilayer are constructed using a 2D like "tear-and-stack" method, achieving unprecedent control resolution and superior interface quality. Through depth-dependent atomic-scale analysis and electronic reconstruction, the upper and lower STO layers are found near the twisted interface exhibit opposite shear strain, evidencing a strong coupling confined within 2 unit cells (±0.8nm) from the interface. The strain gradient of twisted bilayer STO gives rise to alternating clockwise and counter-clockwise polarization originating from the flexoelectric effect, leading to a large-scale array of polar vortex. This motivates to fabricate twisted STO bilayers with a freestanding parent layer as thin as 0.8nm, in which a polar vortex is also confirmed. The "tear-and-stack" method is generic to create twisted moiré superlattices in a wide range of oxide material systems, and it demonstrates the feasibility of "2D-like" oxide twistronics.

Abstract. Under climate change driven by increased carbon dioxide (CO2) concentrations, stratospheric ozone will respond to temperature and circulation changes, leading to chemistry–climate feedback by modulating large-scale atmospheric circulation and Earth's energy budget. However, there is significant model uncertainty since many processes are involved and few models have a detailed chemistry scheme. This work employs the latest data from Coupled Model Intercomparison Project Phase 6 (CMIP6) to investigate the ozone response to increased CO2. We find that in most models, ozone increases in the upper stratosphere (US) and extratropical lower stratosphere (LS) and decreases in the tropical LS; thus, the total column ozone (TCO) response is small in the tropics. The ozone response is mainly driven by slower chemical destruction cycles in the US and enhanced upwelling in the LS, with a highly model-dependent Arctic ozone response to polar vortex strength changes. We then explore the ozone–climate feedback by combining offline calculations and comparisons between models with (“chem”) and without (“no-chem”) interactive chemistry. We find that the stratospheric temperature response is substantial, with a global negative radiative forcing ranging from −0.03 to −0.19 W m−2. We find that chem models consistently simulate less tropospheric warming and a stronger weakening of the polar stratospheric vortex, which result in a larger increase in sudden stratospheric warming (SSW) frequency than in most no-chem models. Our findings show that ozone–climate feedback is essential for the climate system and should be considered in the development of Earth system models.

Abstract Surface warming in the polar regions has important consequences for the stability of the lowest layers of the atmosphere and for atmospheric vertical movement. Here, using ERA5 reanalysis data and in-situ measurements, we quantify the evolving static stability of the lowest 1km of the Antarctic atmosphere and show that the Brunt-Väisälä frequency, a measure of atmospheric stability, has been steadily decreasing since the 1950s. Using satellite observations, reanalysis and targeted climate simulations, we find that this reduced stability has prompted a shift in prevailing flow regimes over the Antarctic Peninsula by altering regional wind flow and enhancing the generation of orographic gravity waves. Increased gravity wave forcing from the Antarctic Peninsula can have important implications for global-scale circulations, polar vortex strength, ozone depletion and mid-latitude weather.

The influence of tropical oscillations on the thermodynamics of the middle and upper atmosphere at high latitudes was studied using a nonlinear model of the general circulation of the middle and upper atmosphere (MUAM). The observed oscillations include the quasi-biennial oscillation of the zonal wind in the equatorial stratosphere (QBO) and the El Niño–Southern Oscillation (ENSO). The main focus of this work is to study the influence of these oscillations on the strength and persistence of the stratospheric polar vortex. Four ensemble calculations were carried out (10 runs for each QBO and ENSO phase combination) for January–February. It was shown that the polar vortex and Eliassen–Palm (EP) flux divergence were especially strong under La Niña and the westerly QBO phase (wQBO). This was accompanied by a strengthening of the residual mean circulation (RMC) from the summer to the winter hemisphere, causing positive temperature anomalies in the polar mesosphere and negative anomalies in the stratosphere. The greatest RMC weakening and the weakest and warmest polar vortex occurred during El Niño and eQBO conditions in January and during El Niño and wQBO conditions in February. Such diverse manifestations of tropical oscillations via teleconnections can provide valuable information for predicting the frequency and intensity of sudden stratospheric warmings (SSWs) and subsequent extreme cold wave events in the troposphere. Specifically, SSWs are the least probable during La Niña and wQBO conditions in both January and February. The QBO phase most significantly influences the polar vortex during El Niño events in both months. We conclude that SSW development is more favorable during eQBO in January and wQBO in February under El Niño conditions.

Abstract Atmospheric flow underpins virtually all meteorological and climatological phenomena, yet extracting meaningful features from its dynamics remains a major scientific challenge due to its high dimensionality, multi-scale behaviour, and inherent nonlinearity. In this study, we investigate the potential of a network-based framework to reveal the relationships between distinct flow structures. Specifically, we apply three techniques, independent of any particular phenomenon or model, to explore patterns of coherence and information transfer, vortical interactions, and Lagrangian coherent structures. We assess their utility using a rotating shallow-water model of the stratospheric polar vortex, which reproduces key aspects of wintertime dynamics, including sudden stratospheric warming split events. Our results support three central claims. First, the transformation of fluid flow data into a network representation preserves essential dynamical information. Second, this representation enables a more accessible and structured analysis of the underlying dynamical structures. Third, multiple types of networks can be constructed from atmospheric flow data, each offering distinct yet complementary insights into the system’s collective behaviour. Together, these findings highlight the potential of network-based approaches as valuable tools in atmospheric research.

Unprecedented abnormal cold weather with snowfall in eastern Southern Africa associated with a disturbed stratospheric south polar vortex: 21 September 2024 storm

Abstract Compound dry–hot conditions increasingly threaten South and Southeast Asia, highlighting the need to understand drivers. Observations and numerical simulations reveal a robust polar–low‐latitude teleconnection: the March Arctic stratospheric polar vortex (ASPV) strongly modulates March–April compound dry–hot conditions across the region. When the March ASPV weakens, anomalous easterlies in the lower Arctic stratosphere induce corresponding tropospheric easterlies and persist through April, cooling Siberia and accelerating the mid‐latitude westerlies. The resulting anticyclonic shear drives an anomalous anticyclone over northern South and Southeast Asia. Combined with the region's climatologically dry–hot season, these processes promote compound dry–hot conditions further amplified by positive soil moisture–atmosphere feedback. Moreover, the March ASPV outweighs the preceding winter tropical sea surface temperature in shaping compound dry–hot variability in this northern sector. Our results highlight the critical role of the Arctic stratospheric anomalies in driving low‐latitude climate, helping improve risk mitigation.

Abstract Rapid extreme temperature swings, termed “temperature whiplashes”, can lead to significant socioeconomic impacts. Few studies have considered temperature whiplashes over continental or global domains, but regional characteristics of temperature whiplash events and the potential for long-range predictions of such events remain to be studied. This study focuses on defining and characterizing temperature whiplash events in the United States Southern Plains during the winter. Two types of whiplashes are defined: (1) hot-to-cold and (2) cold-to-hot. Using the European Centre for Medium-Range Weather Forecasts Fifth Reanalysis from 1950–2023 during December to February, temperature whiplash events are defined using a Temperature Swing Index (TSI), a measure of day-to-day changes in temperature, area-averaged across the Southern Plains. Days where the TSI exceeds the 90 th percentile are labeled “high swing days” (HSD). Temperature whiplash events occur when a HSD coincides with a highly negative (hot-to-cold) or positive (cold-to-high) shift in temperatures. Lagged geopotential height composites of hot-to-cold whiplashes illustrate an amplifying Rossby wavetrain and atmospheric blocking pattern in the North Pacific in the mid-troposphere, coinciding with an increasingly distorted and “stretched” stratospheric polar vortex at 50 hPa. Coinciding with a statistically significant upward flux over eastern Siberia/western Alaska and downward flux over Canada, our results suggest possible stratospheric wave reflection prior to the HSD. These characteristics present particular forecasts of opportunity that may improve predictions of these extreme temperature events on a subseasonal-to-seasonal scale.

Sudden Stratospheric Warmings (SSWs) are extreme polar atmospheric disturbances that significantly impact mid-latitude cold surges, but their early prediction remains a challenge for conventional numerical models. In this study, we propose a video prediction framework for SSW forecasting and introduce a Decoupled Spatiotemporal Memory Flow Network (DSMF-Net) to more effectively capture the dynamic evolution of stratospheric polar vortices. DSMF-Net separates spatial and temporal dependencies using specialized memory flow modules, enabling fine-grained modeling of vortex morphology and dynamic transitions. Experiments on representative SSW events from 2018 to 2021 show that DSMF-Net can reliably predict SSW occurrences up to 20 days in advance while accurately replicating the evolution of polar vortex structures. Compared to baseline models such as the Predictive Recurrent Neural Network (PredRNN) and Motion Recurrent Neural Network (MotionRNN), our method achieves consistent improvements across various metrics, with average gains of 10.5% in Mean Squared Error (MSE) and 6.4% in Mean Absolute Error (MAE) and a 0.7% increase in the Structural Similarity Index Measure (SSIM). These findings underscore the potential of deep video prediction frameworks to improve medium-range stratospheric forecasts and bridge the gap between data-driven models and atmospheric dynamics.

Abstract. The Svalbard Archipelago, highly sensitive to rapid environmental changes, offers an ideal physical laboratory to investigate how environmental drivers can shape the seasonal chemical composition of snow in a warming climate. From 2018 to 2021, sampling campaigns at the Gruvebadet Snow Research Site in Ny-Ålesund, in the North-West of the Svalbard Archipelago, captured the interannual variability in ionic and elemental impurities within surface snow, reflecting seasonal differences in atmospheric and oceanic conditions. Notably, warmer conditions prevailed in 2018–2019 and 2020–2021, contrasting with the relatively colder season of 2019–2020. Our findings suggest that impurity concentrations in the 2019–2020 colder season are impacted by enhanced sea spray aerosol production, likely driven by a larger extent of sea ice, and drier, windy conditions. This phenomenon was particularly evident in March 2020, when extensive sea ice was present in Kongsfjorden and around Spitsbergen due to an exceptionally strong, cold stratospheric polar vortex and unusual Arctic Oscillation (AO) index positive phase. This study provides a detailed characterization of how snow chemistry in this area responds to major environmental conditions, with particular attention to sea-ice extent, atmospheric circulation, synoptic conditions, and Arctic climate variability.

Abstract We present the long‐term trends of the Arctic stratospheric polar vortex (SPV) using the Modern Era Retrospective Research analysis for Research and Application‐2 (MERRA‐2) reanalysis data, and assess its impact on the mesosphere and lower thermosphere (MLT) using Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (SD‐WACCM‐X) simulations. Our findings reveal that the SPV showed a weakening trend from 1980 until the early 2000s, but a strengthening trend after the 2000s. This change is attributed to the weakening of the planetary wave (PW) activities, particularly the wavenumber‐1, which can be driven by long‐term Arctic surface changes. A strong link has been found between the observed PWs activity and the increasing sea surface temperature (SST) over/nearby the Barents‐Kara Sea before early 2000s and over the Central North Pacific region after the 2000s. Furthermore, we observe that the SPV trend influences the zonal mean zonal winds and migrating solar semidiurnal tide (SW2) in the MLT. The SW2 exhibits a ∼13%/decade positive trend from 1980 to the early 2000s and a ∼14%/decade negative trend after 2000s. These results provide evidence of the impact of Arctic surface variabilities, including sea‐ice, on the MLT dynamics, especially SW2 tide.

Abstract. This study investigates Quasi-Biennial Oscillation (QBO) teleconnections and their modulation by the El Niño–Southern Oscillation (ENSO) using a multi-model ensemble from the Atmospheric Processes And their Role in Climate (APARC) QBO initiative (QBOi). Analyzing observed QBO–ENSO teleconnections is challenging because it is difficult to separate the respective influences of QBO and ENSO outside the QBO region due to aliasing in the historical record. To isolate these signals, simulations were conducted with annually repeating prescribed sea-surface temperatures (SSTs) representing idealized El Niño and La Niña conditions (the QBOi EN and LN experiments, respectively), and results are compared with the QBOi control experiment (CTL) under ENSO-neutral conditions. The strength of the Holton-Tan relationship between the phase of the QBO and the strength of the polar vortex seen in observations is reproduced in fewer than three models in CTL and by one model in EN. In LN, three out of nine models reproduce the observed Holton–Tan relationship, but with less than half of the observed amplitude. In the Arctic winter climate, sudden stratospheric warmings (SSWs) occur more frequently in EN than in LN; however, unlike in observations, there is no discernible difference in SSW frequency between QBO westerly (QBO-W) and QBO easterly (QBO-E) phases. The Asia-Pacific subtropical jet (APJ) shifts significantly equatorward during QBO-W compared to QBO-E in observations, but this shift is not robust across models, regardless of ENSO phases. In the tropics, the sign and spatial pattern of the QBO precipitation response vary widely across models and experiments, indicating that any potential QBO signal is strongly modulated by the prevailing ENSO phases. Overall, the QBOi models exhibit unrealistically weak QBO wind amplitudes in the lower stratosphere, which may explain the weak polar vortex and APJ responses, as well as the weak precipitation signals in the tropics. In contrast, the QBO teleconnection with the Walker circulation during boreal summer and autumn shows consistent signals in both observations and most models. Specifically, the QBO-W phase is characterized by upper-level westerly and lower-level easterly anomalies over the Indian Ocean–Maritime Continent relative to QBO-E, although the amplitude and timing of these anomalies remain model-dependent. Notably, the influence of QBO phase on the Walker circulation appears insensitive to the ENSO phase.