Ocean dynamics are often sidelined in exoplanet climate studies due to the high computational cost of fully coupled atmosphere-ocean general circulation models (GCMs). However, ocean heat transport (OHT) can play a critical role in shaping the climate and observables of terrestrial planets. As a compromise, most exoplanet GCMs rely on slab ocean models without OHT. Here, we present an improved compromise - a fast and physically grounded dynamical slab ocean model, implemented in the Generic Planetary Climate Model (Generic-PCM). The model extends previous frameworks by incorporating a Sverdrup balance formulation for wind-driven Ekman transport, the first application of the Gent-McWilliams parameterisation of mesoscale eddies in a slab ocean model, and a spectrally and thickness-dependent treatment of sea ice and snow albedo. In aquaplanet simulations, enabling OHT produces substantial changes in both surface climate and atmospheric circulation, including cooler tropical sea surface temperatures, reduced sea ice, and the emergence of a double-banded equatorial precipitation pattern driven by Ekman-induced upwelling. The resulting OHT profiles show first-order agreement with fully coupled atmosphere-ocean GCMs. Applied to modern Earth, the model reproduces key large-scale climate properties, including a global mean surface temperature of 13°C (within 1°C of observations), planetary albedo of 0.32 (within 0.01), and sea ice extent with significantly reduced seasonal biases relative to simulations without OHT. Due to model parallelisation, these improvements are achieved at almost no additional computation cost compared to OHT-disabled simulations run over the same number of model years. This enables long integrations, making the model particularly well suited for exoplanet and paleoclimate studies where broad parameter exploration is essential.

We present an improved dynamical slab ocean model implemented in a 3-D General Circulation Model (GCM) called the Generic Planetary Climate Model (Generic-PCM; formerly the LMD-Generic GCM). Earlier two-layer slab ocean models featured wind-driven Ekman transport, horizontal diffusion and convective adjustment. Building upon this, our updated parallelised model introduces a Sverdrup balance scheme for Ekman transport, the first application of the Gent-McWilliams (GM) parameterisation of mesoscale eddies in a slab ocean model, and a spectrally and thickness dependent formulation of sea ice and snow albedo. We validate this model in an idealised aquaplanet setting under various OHT configurations. We show that enabling OHT transforms not only surface features - such as cooler tropical sea surface temperatures (SSTs) and reduced sea ice coverage - but also atmospheric structures, notably producing a double-banded precipitation pattern across the equator driven by Ekman-induced upwelling. Our modelled meridional OHT profiles show first-order agreement with fully coupled atmosphere-ocean GCMs, with Ekman transport dominating in the tropics (enhanced by GM-induced restratification), and diffusive plus GM contributions peaking near the ice edge. When applied to modern Earth, the OHT-enabled configuration yields an annual global average surface temperature of 13 degrees C, within 1 degrees C of reanalysis estimates, and improves extrapolar SSTs and sea ice coverage relative to the OHT-disabled baseline. Seasonal SST and sea ice biases relative to observations are also significantly reduced to within 0.6 degrees C and 3 million km2, respectively. We obtain a planetary bond albedo of around 0.32, in close agreement with observations. Together, the aquaplanet and modern Earth benchmarks demonstrate that our developments represent a clear improvement over earlier two-layer implementations. We further show that GM-induced restratification reduces the need for explicit convective adjustment, while also strengthening Ekman transport. In addition to improving equatorial dynamics, the inclusion of the Sverdrup balance also reduces hemispheric asymmetries. Notably, due to model parallelisation, these improvements are achieved at almost no additional computational cost compared to OHT-disabled simulations run over the same number of model years. This enables long integrations and large ensemble studies, making the model particularly well suited for exoplanet and paleoclimate studies where broad parameter exploration is essential.

The past four decades have witnessed a strengthening of the winter anticyclonic circulation over the Barents-Kara Sea (BKS), a change that has contributed substantially to amplified local warming and sea ice loss, as well as to Eurasian cooling. However, the cause of this trend in the BKS atmospheric circulation remains unknown. Here we show that anthropogenic greenhouse gases are the primary driver of the strengthening of the BKS anticyclonic circulation, with anthropogenic aerosols playing a secondary role, both together accounting for about 86% of the observed circulation trend. Both forcings induce an amplified BKS low-tropospheric warming through coupling with strong sea ice loss. This amplified warming raises geopotential height aloft through thermal expansion, causing an anomalous anticyclonic anomaly, which in turn enhances warming and sea ice loss, forming a positive feedback loop. Our work provides a theoretical framework for understanding Arctic atmospheric circulation responses to anthropogenic warming and may have implications for climate and environment in the Arctic and beyond.

In many regions, extreme temperatures increase faster than background global warming due to complex atmospheric circulation changes. This has been overlooked in Antarctica. Here, we examine extreme temperatures recorded at 16 weather stations since 1950, and identify their changes and drivers. Over the Antarctic Peninsula and the South Pole, 10-year return level temperatures increased by up to 1.19°C per decade since 1980, outpacing mean temperature trends. Most extreme events, including statistically implausible or black swan events, were driven by intense atmospheric rivers linked to Rossby wave trains forced by tropical Pacific convection. In contrast, 10-year return level temperature decreased over most of East Antarctica, despite increasing atmospheric river activity, as the mean cooling muted the impacts of warm intrusion until recently. Our results highlight how the entire continent could become vulnerable in a warmer climate or enhanced tropical convective activity, as illustrated by the March 2022 heatwave.

Antarctic atmospheric rivers (ARs) are a form of extreme weather that transport heat and moisture from the Southern Hemisphere subtropics and/or mid-latitudes to the Antarctic continent. Present-day AR events generally have a positive influence on the Antarctic ice-sheet mass balance by producing heavy snowfall, yet they also cause melt of sea ice and coastal ice sheet areas, as well as ice shelf destabilization. In this Review, we explore the atmospheric dynamics and impacts of Antarctic ARs over their life cycle to better understand their net contributions to ice-sheet mass balance. ARs occur in high-amplitude pressure couplets, and those strong enough to reach the Antarctic are often formed within Rossby waves initiated by tropical convection. Antarctic ARs are rare events (~3 days per year per location) but have been responsible for 50–70% of extreme snowfall events in East Antarctica since the 1980s. However, they can also trigger extensive surface melting events, such as the final ice shelf collapse of Larsen A in 1995 and Larsen B in 2002. Climate change will likely cause stronger ARs as anthropogenic warming increases atmospheric water vapour. Future research must determine how these climate change impacts will alter the relationship among Antarctic ARs, net ice-sheet mass balance and future sea-level rise. Atmospheric rivers provide the majority of water vapour transport to the high latitudes. This Review summarizes Antarctic atmospheric river dynamics and climatology and discusses their impacts on the mass balance of the Antarctic ice sheet.

Despite their relative rarity, atmospheric rivers are key contributors to the surface mass balance of Antarctica. However, the future role of atmospheric rivers in modulating Antarctic sea-level contributions is a major area of uncertainty. Here, we leverage high-resolution climate simulations to show that Antarctic atmospheric rivers are highly sensitive to future increases in atmospheric moisture, leading to a doubling of atmospheric river frequencies and 2.5 × increase in precipitation from 2066-2100 under present-day thresholds for atmospheric river detection. However, future precipitation impacts are critically dependent on the detection threshold: accounting for moisture increases in the threshold produces smaller, regional changes in atmospheric river frequency, primarily resulting from an eastward shift in the polar jet maximum wind speeds. Our results underscore the importance of using large ensembles to quantify Antarctic atmospheric river responses to variability in projected moisture, which may not be captured when using only a few ensemble members.

Atmospheric Rivers (AR) are extreme hydrological events that have strong impacts on the different components of the Antarctic ice sheet surface mass balance (SMB), through both snow accumulation and surface melt due to heating and rain. Their evolving characteristics are therefore important to understand for an accurate prediction of future SMB changes. We use here an ensemble of simulations of the mid-21st century climate using the IPSL-CM6 model. The future Antarctic ARs are identified using a detection algorithm adapted to the region, and taking into account in the detection threshold (based on moisture fluxes) the rising background moisture in a warmer climate. While a constant detection threshold leads to a continuous increase of the number of ARs detected, the use of this adaptative threshold leads instead to a relatively stable frequency of occurence, but with a larger penetration over Antarctica (+5% occurence over the continent). In addition, a wave number 3 component appears in the future change in frequency, as well as in AR-related snowfall. While the number of ARs does not change much, their intensity, as measured by the associated water vapor transport, increases in line with the Clausius-Clapeyron relation. Their different impacts on the SMB also become larger, with both increasing snowfall, and surface melt and rainfall in the coastal regions. The direct effect on the SMB is however dominated by the increase in snow accumulation.

Ocean modelling is often sidelined by exoclimate modellers, mostly due to the associated computational expense of spinning up dynamic oceans. However, oceanic heat transport can critically impact the climate and observables for M-planets in the middle of their habitable zones (e.g., [1]) like TRAPPIST-1e. The oceanic description can also affect the number of final stable climatic states of the planet ([2]). Short of using a fully dynamic ocean model, a compromise used in most exoplanet General Circulation Models (GCMs) is a slab ocean model without oceanic heat transport.Here, we will first present our improved compromise - the new dynamical slab ocean model integrated into the Generic-PCM ([3]), previously known as the LMD Generic GCM (e.g., [4]). Our parallelisable ocean model not only accounts for sea-ice/snow evolution, but also features wind-driven ocean transport (Ekman transport), horizontal eddy diffusion and convective adjustment between oceanic layers. When coupled with the atmosphere, it effectively reproduces critical attributes observed on modern Earth, including the major oceanic heat flows, an annually averaged surface temperature of 13 C, planetary albedo of 0.32 and sea ice coverage spanning 18 million sq. km.Further, we will delve into the implications of a dynamical slab ocean model for TRAPPIST-1e. Despite recent JWST observations indicating the lack of a (thick) atmosphere for TRAPPIST-1b ([5]) and 1c ([6]), the planets farther away from the star, like 1e, may have retained moderately thick atmospheres. Assuming this, and if 1e formed with a substantial water reservoir ([7]), it could have sustained liquid water oceans ([8]). In general, the presence of oceanic heat transport can give rise to distinct oceanic patterns, as illustrated by the “lobster” pattern observed for Proxima Centauri b by [9], in contrast to the “eyeball” pattern in [4], observed in its absence. Moreover, studies suggest that the climates of Proxima Centauri b and TRAPPIST-1e may share similarities ([4], [8]). In this context, we will present findings from our new dynamical slab ocean within the Generic-PCM for TRAPPIST-1e. These results will then be systematically compared with those of [9], which used ROCKE-3D ([10]) with a dynamic ocean model. We believe that this will help in strengthening our understanding of the climate of TRAPPIST-1e and also offer insights into comparative exoplanetary climate research. Finally, we will discuss our findings in the context of habitability, particularly emphasising the role of a dynamical ocean model in informing our understanding of habitable conditions. References:[1] Yang et al. (2019b)[2] Brunetti et al. (2019)[3] Forget et al. (in prep)[4] Turbet et al. (2016)[5] Greene et al. (2023)[6] Zieba et al. (2023)[7] Tian & Ida (2015)[8] Turbet et al. (2018)[9] Del-Genio et al. (2019)[10] Way et al. (2017)

Between 15 and 19 March 2022, East Antarctica experienced an exceptional heat wave with widespread 30 degrees-40 degrees C temperature anomalies across the ice sheet. This record-shattering event saw numerous monthly temperature records being broken including a new all-time temperature record of -9.4 degrees C on 18 March at Concordia Station despite March typically being a transition month to the Antarctic coreless winter. The driver for these temperature extremes was an intense atmospheric river advecting subtropical/midlatitude heat and moisture deep into the Antarctic interior. The scope of the temperature records spurred a large, diverse collaborative effort to study the heat wave's meteorological drivers, impacts, and historical climate context. Here we focus on describing those temperature records along with the intricate meteorological drivers that led to the most intense atmospheric river observed over East Antarctica. These efforts describe the Rossby wave activity forced from intense tropical convection over the Indian Ocean. This led to an atmospheric river and warm conveyor belt intensification near the coastline, which reinforced atmospheric blocking deep into East Antarctica. The resulting moisture flux and upper-level warm-air advection eroded the typical surface temperature inversions over the ice sheet. At the peak of the heat wave, an area of 3.3 million km(2) in East Antarctica exceeded previous March monthly temperature records. Despite a temperature anomaly return time of about 100 years, a closer recurrence of such an event is possible under future climate projections. In Part II we describe the various impacts this extreme event had on the East Antarctic cryosphere. SIGNIFICANCE STATEMENT: In March 2022, a heat wave and atmospheric river caused some of the highest temperature anomalies ever observed globally and captured the attention of the Antarctic science community. Using our diverse collective expertise, we explored the causes of the event and have placed it within a historical climate context. One key takeaway is that Antarctic climate extremes are highly sensitive to perturbations in the midlatitudes and subtropics. This heat wave redefined our expectations of the Antarctic climate. Despite the rare chance of occurrence based on past climate, a future temperature extreme event of similar magnitude is possible, especially given anthropogenic climate change.

During atmospheric river (AR) landfalls on the Antarctic ice sheet, the high waviness of the circumpolar polar jet stream allows for sub-tropical air masses to be advected towards the Antarctic coastline. These rare but high-impact AR events are highly consequential for the Antarctic mass balance; yet little is known about the various atmospheric dynamical components determining their life cycle. By using an AR detection algorithm to retrieve AR landfalls at Dumont d’Urville and non-AR analogues based on 700 hPa geopotential height, we examined what makes AR landfalls unique and studied the complete life cycle of ARs to affect Dumont d’Urville. ARs form in the mid-latitudes/sub-tropics in areas of high surface evaporation, likely in response to tropical deep convection anomalies. These convection anomalies likely lead to Rossby wave trains that help amplify the upper-tropospheric flow pattern. As the AR approaches Antarctica, condensation of isentropically lifted moisture causes latent heat release that – in conjunction with poleward warm air advection – induces geopotential height rises and anticyclonic upper-level potential vorticity tendencies downstream. As evidenced by a blocking index, these tendencies lead to enhanced ridging/blocking that persist beyond the AR landfall time, sustaining warm air advection onto the ice sheet. Finally, we demonstrate a connection between tropopause polar vortices and mid-latitude cyclogenesis in an AR case study. Overall, the non-AR analogues reveal that the amplified jet pattern observed during AR landfalls is a result of enhanced poleward moisture transport and associated diabatic heating which is likely impossible to replicate without strong moisture transport.

Between 15 and 19 March 2022, East Antarctica experienced an exceptional heat wave with widespread 30 degrees-40 degrees C temperature anomalies across the ice sheet. In Part I, we assessed the meteorological drivers that generated an intense atmospheric river (AR) that caused these record-shattering temperature anomalies. Here, we continue our large collaborative study by analyzing the widespread and diverse impacts driven by the AR landfall. These impacts included widespread rain and surface melt that was recorded along coastal areas, but this was outweighed by widespread high snowfall accumulations resulting in a largely positive surface mass balance contribution to the East Antarctic region. An analysis of the surface energy budget indicated that widespread downward longwave radiation anomalies caused by large cloudliquid water contents along with some scattered solar radiation produced intense surface warming. Isotope measurements of the moisture were highly elevated, likely imprinting a strong signal for past climate reconstructions. The AR event attenuated cosmic ray measurements at Concordia, something previously never observed. Last, an extratropical cyclone west of the AR landfall likely triggered the final collapse of the critically unstable Conger Ice Shelf while further reducing an already record low sea ice extent.

Atmospheric rivers (ARs) are extreme hydrological events that have strong impacts on the Antarctic surface mass balance (SMB), through both snow accumulation and surface melt due to heating and rain. To estimate their impacts on future SMB, we study Antarctic ARs in an ensemble of 21st century simulations. While the number of detected ARs increases continuously when using a constant detection threshold based on historical moisture fluxes, it remains stable with an adaptive threshold evolving with the rising background moisture. However, ARs penetrate further into Antarctica following a wave number 3 pattern. In addition, the intensity of Antarctic ARs, measured by moisture fluxes, is simulated to increase following the Clausius-Clapeyron relation. The opposing SMB impacts become larger, with both increasing snowfall, and coastal surface melt and rainfall. Yet, their overall influence on the SMB is dominated by increased snow accumulation.

The parameterization scheme that represents gravity waves due to convection in LMDz-6A, the atmospheric components of the IPSL coupled climate model (IPSLCM6), is directly compared to Strateole-2 balloon observations made in the lower tropical stratosphere from November 2019 to February 2020. The input meteorological fields necessary to run the parameterization offline are extracted from the ERA5 reanalysis and correspond to the instantaneous meteorological conditions found underneath the balloons. In general, we find a fair agreement between measurements of the momentum fluxes due to waves with periods less than 1 hr and the parameterization. The correlation of the daily values between the observations and the results of the parameterization is around 0.4, which is statistically elevated considering that we analyze around 600 days of data and surprisingly good considering that the parameterization has not been tuned: the scheme is just the standard one that helps producing a quasi-biennial oscillation (QBO) in the IPSLCM6 model. Online simulations also show that the measured values of momentum fluxes are well representative of the zonally and averaged values of momentum fluxes needed in LMDz-6A to simulate a QBO. The observations also show that longer waves with periods smaller than a day carry about twice as much flux as waves with periods smaller than an hour, which is a challenge since the low period waves that make the difference are potentially in the "gray zone " of most climate models.

The climate responses to Atlantic meridional overturning circulation (AMOC) fluctuations are investigated in a hierarchy of sensitivity experiments. We modify the baroclinic component of the North Atlantic Ocean currents online in an atmosphere-ocean general circulation model to reproduce typical AMOC multidecadal variability found in a preindustrial control simulation in the same model. An analogous experiment is also conducted using a slab-ocean experiment. The responses to a strong AMOC include a widespread warming in the Northern Hemisphere and a northward shift of the intertropical convergence zone over the Atlantic Ocean. The driving mechanism of climate responses is then investigated with the changes in the energy flows in the ocean and atmosphere. The large-scale atmospheric changes in the tropics are organized by an anomalous cross-equatorial Hadley circulation transporting energy southward and moisture and heat northward. Changes in the Indo-Pacific Ocean circulation and heat transport, driven by the wind stress associated with the abnormal Hadley cell, damp the atmospheric responses. The lack of Indo-Pacific transport and ocean heat storage leads to amplified atmospheric changes in the slab-ocean experiments, which are further amplified by a positive feedback due to the interhemispheric antisymmetric changes in low cloud cover.

ETIN-MIP is a community-wide effort to improve dynamical understanding of the linkages between tropical precipitation and radiative biases in various regions, with implications for anthropogenic climate change and geoengineering.

The last two decades have seen a dramatic decline and strong year-to-year variability in Arctic winter sea ice, especially in the Barents-Kara Sea (BKS), changes that have been linked to extreme midlatitude weather and climate. It has been suggested that these changes in winter sea ice arise largely from a combined effect of oceanic and atmospheric processes, but the relative importance of these processes is not well established. Here, we explore the role of atmospheric circulation patterns on BKS winter sea ice variability and trends using observations and climate model simulations. We find that BKS winter sea ice variability is primarily driven by a strong anticyclonic anomaly over the region, which explains more than 50% of the interannual variability in BKS sea-ice concentration (SIC). Recent intensification of the anticyclonic anomaly has warmed and moistened the lower atmosphere in the BKS by poleward transport of moist-static energy and local processes, resulting in an increase in downwelling longwave radiation. Our results demonstrate that the observed BKS winter sea-ice variability is primarily driven by atmospheric, rather than oceanic, processes and suggest a persistent role of atmospheric forcing in future Arctic winter sea ice loss.

The disintegration of the ice shelves along the Antarctic Peninsula have spurred much discussion on the various processes leading to their eventual dramatic collapse, but without a consensus on an atmospheric forcing that could connect these processes. Here, using an atmospheric river detection algorithm along with a regional climate model and satellite observations, we show that the most intense atmospheric rivers induce extremes in temperature, surface melt, sea-ice disintegration, or large swells that destabilize the ice shelves with 40% probability. This was observed during the collapses of the Larsen A and B ice shelves during the summers of 1995 and 2002 respectively. Overall, 60% of calving events from 2000–2020 were triggered by atmospheric rivers. The loss of the buttressing effect from these ice shelves leads to further continental ice loss and subsequent sea-level rise. Under future warming projections, the Larsen C ice shelf will be at-risk from the same processes.

Sur une grande partie de l'Antarctique, le bilan de masse (c'est-à-dire de neige) de surface est dominé par quelques événements de précipitations extrêmes. Ces événements dépendent d'intrusions de masses d'air très humide associées à des phénomènes dénommés rivières atmosphériques en provenance de l'océan Austral. Ces rivières atmosphériques influencent fortement le climat ; pourtant, les caractéristiques, les mécanismes et les impacts associés restent mal connus en Antarctique. Nous résumons ici l'état des connaissances sur la mise en place de ces événements extrêmes et leurs impacts à la fois sur l'accumulation de neige, le réchauffement et la fonte en surface de la calotte. Over much of Antarctica, the surface mass balance (i.e. the resultant of snow fluxes at the surface of the ice sheet) is dominated by a few extreme precipitation events. It has recently been shown that these events are linked to intrusions of highly humid air masses related with atmospheric rivers traversing the Southern Ocean. These atmospheric rivers strongly influence the climate, yet their meteorological characterization and associated impacts remain poorly understood in Antarctica. We summarize here the latest research regarding the development of these extreme events and their impacts on snow accumulation, warming, and surface melt on the Antarctic ice sheet.

A pronounced multi-centennial variability of the Atlantic meridional overturning circulation (AMOC) is found to be regulated by the salinity exchanges between the Atlantic and Arctic ocean in the IPSL-CM6A-LR atmosphere-ocean coupled model. The AMOC variations are preceded by salinity-driven density anomalies in the main deep convection sites in the Labrador and Greenland seas. Associated with a strong AMOC, the Arctic sea ice export through the Fram Strait reduces due to the decreased sea ice volume and anomalous northward currents. Anomalous freshwater hence accumulates at the surface in the Central Arctic. Meanwhile, the enhanced Atlantic inflow enters the Arctic through the Barents Sea and leads to a positive salinity in the Eastern Arctic subsurface. The surface freshwater anomalies last for 4 to 5 decades before they eventually reach the Lincoln Sea north of Greenland. The associated oceanic currents around Greenland reorganize, favoring the anomalous Arctic freshwater export to the North Atlantic and intensifying the stratification in deep convection sites. The AMOC then weakens, and the Central Arctic presents a positive surface salinity anomaly in turn. The oscillation switches to the opposite phase. These AMOC and sea ice fluctuations modulate climate worldwide, with a strong AMOC leading to a warming of 0.4°C in the northern extratropics, reaching up to 1°C in the Arctic lower troposphere during winter. In all seasons, a northward displacement of the intertropical convergence zone is also simulated.