Explore the vast range of titles available.

This study investigates the specific circulation anomalies that have sustained the low Antarctic sea ice state since 2016. Firstly, we find a significant strengthening and southward shift in the Ferrel Cell (FC) during 2016–2022, resulting in a marked increase in southward transport of heat and moisture. Secondly, this enhanced FC is closely associated with a stronger mid‐latitude wave pattern. This pattern is zonally asymmetric and greatly amplifies the poleward advections of heat and moisture, leading to the increased downward longwave radiation, more liquid precipitation and sea ice retreat in specific regions, including the western Pacific and Indian Ocean sectors, Ross and northern Weddell Seas. The mechanism deduced from the short‐term period is further supported by the results of 40 ensemble members of simulations. The southward expansion of the FC and sea ice decline are closely linked to La Niña‐like conditions but may also be driven by anthropogenic global warming. Plain Language Summary Following the sudden decline in 2016, the Antarctic sea ice extent has persisted at historically low levels. In 2023, it reached unprecedented record lows. However, the specific atmospheric circulation anomalies that have sustained the Antarctic sea ice at low levels are still unknown. It is well‐established that the Ferrel Cell, a mid‐latitude atmospheric meridional circulation, plays a pivotal role in the energy exchange between the high‐ and mid‐latitudes. Our findings indicate that the enhanced Ferrel Cell zonally intensified southward transport of heat and moisture over the sea ice regions, which sustains the overall low Antarctic sea ice state. Additionally, in the horizontal plane, the enhanced mid‐latitude wave pattern is responsible for the regional sea ice retreat over the western Pacific sector, Ross Sea, Indian Ocean sector, and northern Weddell Sea, and is also closely associated with the enhanced Ferrel Cell. The effects of the enhanced Ferrel Cell on Antarctic sea ice decline are further supported by the results of large ensemble simulations. Therefore, this study suggests that concurrent with the southward shifting of the Ferrel Cell, the stronger warm and moist air intrusions, and the increased liquid precipitation, restrict the Antarctic sea ice expansion following its sudden decline. Key Points Since 2016, the low Antarctic sea ice extent has persisted, consistent with heat and moisture accumulation over the sea ice edges The Ferrel Cell was enhanced and shifted southward, leading to the increased southward heat/moisture advection, and liquid precipitation The effects of the enhanced Ferrel Cell on Antarctic sea ice decline are further supported by the results of large ensemble simulations

In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the EastAsian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key region where the June sea-icevariability exerts the most significant impacts on the East Asian August tripole rainfall pattern, and explores the teleconnectionmechanisms involved. The results reveal that a reduction in June sea ice excites anomalous upward air motion due to strongnear-surface thermal forcing, which further triggers a meridionalAnomalous downward motion therefore forms over the Caspianoverturning wave-like pattern extending to midlatitudes.Sea, which in turn induces zonally oriented overturningcirculation along the subtropical jet stream, exhibiting the east-west Rossby wave train known as the Silk Road pattern. It issuggested that the Bonin high, a subtropical anticyclone predominant near South Korea, shows a significant anomaly due tothe eastward extension of the Silk Road pattern to East Asia. As a possible descending branch of the Hadley cell, the Boninhigh anomaly ultimately triggers a meridional overturning, establishing the Pacific-Japan pattern. This in turn induces ananomalous anticyclone and cyclone pair over East Asia, and a tripole vertical convection anomaly meridionally oriented overEast Asia. Consequently, a tripole rainfall anomaly pattern is observed over East Asia. Results from numerical experimentsusing version 5 of the Community Atmosphere Model support the interpretation of this chain of events.

Previous studies have indicated the modulation of the Madden–Julian oscillation (MJO) by the Quasi-Biennial Oscillation (QBO) and the influence of the MJO on surface temperature over Eurasia during boreal winter. The present study reveals that the MJO-related circulation anomalies are different in easterly and westerly QBO years, leading to distinct surface temperature anomaly patterns over Eurasia. During the easterly QBO years, the surface air temperature anomalies over Eurasia display a meridional dipole pattern in MJO phase 2 associated with the mid-latitude surface anticyclonic anomalies. The development of surface anomalous anticyclone is attributed to a combined effect of negative North Atlantic Oscillation (NAO)-related mid-latitude wave train and stronger MJO convection triggered poleward propagation of Rossby wave train. The negative NAO is related to the easterly QBO through the Holton–Tan relationship. The anomalous overturning circulation excited by the stronger MJO convection in easterly QBO years also contributes to the development and eastward extension of anomalous anticyclone. The anticyclonic anomalies induce the meridional temperature anomaly pattern by horizontal advection. During the westerly QBO years, the surface air temperature anomalies over Eurasia show a zonal alternating pattern in MJO phase 3, which corresponds to the development of mid-latitude Rossby wave train associated with positive NAO with a stronger MJO–NAO connection in westerly QBO years. The MJO convection induces upper-level divergent wind anomalies, contributing partially to the development of the Rossby wave source and helping the building of the mid-latitude wave train. The zonal temperature anomalies over Eurasia are also contributed by the horizontal advection associated with surface cyclonic anomalies.

Summer weather extremes are often associated with high‐amplitude atmospheric planetary waves (Petoukhov et al., 2013). Such conditions lead to stationary weather patterns, triggering heat waves and sometimes prolonged intense rainfall. These wave events, referred to as periods of Quasi‐Resonant Amplification (QRA), are relatively rare though and hence provide only a few data points in the meteorological record to analyse. Here, we use atmospheric models coupled to boundary conditions that have evolved slowly (i.e., climate), to supplement measurements. Specifically we assess altered probabilities of resonant episodes by employing a unique massive ensemble of atmosphere‐only climate simulations to populate statistical distributions of event occurrence. We focus on amplified waves during the two most extreme European heat waves on record, in years 2003 and 2015 (Russo et al., 2015). These years are compared with other modelled recent years (1987–2011), and critically against a modelled world without climate change. We find that there are differences in the statistical characteristics of wave event likelihood between years, suggesting a strong dependence on the known and prescribed Sea Surface Temperature (SST) patterns. The differences are larger than those projected to have occurred under climate change since the pre‐industrial period. However, this feature of small differences since pre‐industrial is based on single large ensembles, with members consisting of a range of estimates of SST adjustment from pre‐industrial to present. Such SST changes are from projections by a set of coupled atmosphere–ocean (AOGCM) climate models. When instead an ensemble for pre‐industrial estimates is subdivided into simulations according to which AOGCM the SST changes are based on, we find differences in QRA occurrence. These differences suggest that to reliably estimate changes to extremes associated with altered amplification of planetary waves, and under future raised greenhouse gas concentrations, likely requires reductions in any spread of future modelled SST patterns. Summer mid‐latitudes can experience the amplification of planetary waves, and such resonance effects may trigger heat waves. Using a very large ensemble of atmospheric climate simulations, we look to see if the risk of such events is increasing under global warming. Combining a range of CMIP5‐based estimates of forcing sea surface temperature changes (since pre‐industrial times) to drive an atmospheric model, we see little difference overall, although further analysis finds a dependence on any individual estimate of SST alteration.

In recent decades, Arctic summer sea ice extent (SIE) has shown a rapid decline overlaid with large interannual variations, both of which are influenced by geopotential height anomalies over Greenland (GL-high) and the central Arctic (CA-high). In this study, SIE along coastal Siberia (Sib-SIE) and Alaska (Ala-SIE) is found to account for about 65% and 21% of the Arctic SIE interannual variability, respectively. Variability in Ala-SIE is related to the GL-high, whereas variability in Sib-SIE is related to the CA-high. A decreased Ala-SIE is associated with decreased cloud cover and increased easterly winds along the Alaskan coast, promoting ice—albedo feedback. A decreased Sib-SIE is associated with a significant increase in water vapor and downward longwave radiation (DLR) along the Siberian coast. The years 2012 and 2020 with minimum recorded ASIE are used as examples. Compared to climatology, summer 2012 is characterized by a significantly enhanced GL-high with major sea ice loss along the Alaskan coast, while summer 2020 is characterized by an enhanced CA-high with sea ice loss focused along the Siberian coast. In 2012, the lack of cloud cover along the Alaskan coast contributed to an increase in incoming solar radiation, amplifying ice-albedo feedback there; while in 2020, the opposite occurs with an increase in cloud cover along the Alaskan coast, resulting in a slight increase in sea ice there. Along the Siberian coast, increased DLR in 2020 plays a dominant role in sea ice loss, and increased cloud cover and water vapor both contribute to the increased DLR.

This study explores the linkage between summertime temperature fluctuations over midlatitude Eurasia and the preceding Arctic sea ice concentration (SIC) by utilizing the squared norm of the temperature anomaly, the essential part of local eddy available potential energy, as a metric to quantify the temperature fluctuations with weather patterns on various timescales. By comparing groups of singular value decomposition (SVD) analysis, we suggest a significant linkage between strong (weak) August 10-to-30-day temperature fluctuations over mid-west Asia and enhanced (decreased) Barents-Kara Sea ice in the previous February. We find that when the February SIC increases in the Barents-Kara Sea, a zonal dipolar pattern of SST anomalies appears in the Atlantic subpolar region and lasts from February into the summer months. Evidence suggests that in such a background state, the atmospheric circulation changes evidently from July to August, so that the August is characterized by an amplified meridional circulation over Eurasia, weakened westerlies, and high-pressure anomalies along the Arctic coast. Moreover, the 10-to-30-day wave becomes more active in the North Atlantic–Barents-Kara Sea–Central Asia regions and manifests a more evident southward propagation from the Barents-Kara Sea into the Ural region, which is responsible for the enhanced 10-to-30-day wave activity and temperature fluctuations in the region.

Early studies suggested that the Aleutian-Icelandic low seesaw （AIS） features multidecadal variation. In this study, themultidecadal modulation of the AIS and associated surface climate by the Atlantic Multidecadal Oscillation （AMO） duringlate winter （February-March） is explored with observational data. It is shown that, in the cold phase of the AMO （AMOI-）,a clear AIS is established, while this is not the case in the warm phase of the AMO （AMO[＋）. The surface climate overEurasia is significantly influenced by the AMO＇s modulation of the Aleutian low （AL）. For example, the weak AL in AMOI-displays warmer surface temperatures over the entire Far East and along the Russian Arctic coast and into Northern Europe,but only over the Russian Far East in AMO{＋. Similarly, precipitation decreases over central Europe with the weak AL inAMOI-, but decreases over northern Europe and increases over southern Europe in AMOI＋.