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1. Ocean Circulation Change Modulates Tropical Atmospheric Circulation in a Warming Climate: The Role of Ocean Heat Uptake

   https://doi.org/10.1175/JCLI-D-24-0228.1  

   Thomas, Antony P; Liu, Wei (October 2025, Journal of Climate)

   Abstract Deep convection associated with large-scale tropical atmospheric circulations governs tropical precipitation. Under anthropogenic warming, the weakened Walker and Hadley circulations alter tropical rainfall. Ocean circulations are also expected to change due to global warming, impacting tropical atmospheric circulation systems. From the perspective of ocean heat uptake, we investigate how ocean circulation change modulates tropical atmospheric circulation and vertical motion under CO₂warming by comparing fully coupled and slab-ocean simulations. We find that the slowed South Equatorial Current and subtropical cells in the Pacific induce anomalous advective warming, reducing ocean heat uptake in the central-western tropical Pacific. This, combined with increased downward radiation at the top of atmosphere and horizontal moisture advection, escalates the moisture static energy in the air column and promotes ascent in this region, shifting the Pacific Walker circulation eastward and strengthening the Pacific Hadley circulation. Across the tropical Indian Ocean, ocean heat uptake shows a dipole-like change, increasing in the eastern Indian Ocean and seas surrounding marine continents while decreasing in the western Indian Ocean. The former ocean heat uptake increase is triggered by anomalous oceanic vertical advective cooling, which abates the moisture static energy in the air column and inhibits the ascent in the area. The latter ocean heat uptake decrease is prompted by anomalous oceanic advective warming from both horizontal and vertical directions, which enhances the moisture static energy in the air column, resulting in anomalous upward motions. Over most of the tropics, ocean dynamics help attenuate the strengthening of the gross moist stability due to CO₂increase, thereby promoting ascent or weakening descent in the atmosphere. Significance StatementLarge-scale tropical atmospheric circulations are expected to weaken as a result of global warming, having a significant impact on tropical precipitation. Because the atmosphere and oceans are inextricably linked, any subtle change in one can affect the other. For this reason, it is critical to understand the role of ocean circulation change in steering the response of large-scale tropical atmospheric circulation to anthropogenic warming. This study approaches the aforementioned scientific question from the novel perspective of ocean heat uptake. It demonstrates how changes in ocean circulation affect heat uptake over tropical oceans, modifying vertical motion and the Walker and Hadley cells in the tropical atmosphere in a warming climate. 

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2. Changing available energy for extratropical cyclones and associated convection in Northern Hemisphere summer

   https://doi.org/10.1073/pnas.1812312116  

   Gertler, Charles G.; O’Gorman, Paul A. (March 2019, Proceedings of the National Academy of Sciences)

   The circulation of the Northern Hemisphere extratropical troposphere has changed over recent decades, with marked decreases in extratropical cyclone activity and eddy kinetic energy (EKE) in summer and increases in the fraction of precipitation that is convective in all seasons. Decreasing EKE in summer is partly explained by a weakening meridional temperature gradient, but changes in vertical temperature gradients and increasing moisture also affect the mean available potential energy (MAPE), which is the energetic reservoir from which extratropical cyclones draw. Furthermore, the relation of changes in mean thermal structure and moisture to changes in convection associated with extratropical cyclones is poorly understood. Here we calculate trends in MAPE for the Northern extratropics in summer over the years 1979–2017, and we decompose MAPE into both convective and nonconvective components. Nonconvective MAPE decreased over this period, consistent with decreases in EKE and extratropical cyclone activity, but convective MAPE increased, implying an increase in the energy available to convection. Calculations with idealized atmospheres indicate that nonconvective and convective MAPE both increase with increasing mean surface temperature and decrease with decreasing meridional surface temperature gradient, but convective MAPE is relatively more sensitive to the increase in mean surface temperature. These results connect changes in the atmospheric mean state with changes in both large-scale and convective circulations, and they suggest that extratropical cyclones can weaken even as their associated convection becomes more energetic. 

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3. The Role of Tropical, Midlatitude, and Polar Cloud-Radiative Changes for the Midlatitude Circulation Response to Global Warming

   https://doi.org/10.1175/JCLI-D-20-0073.1  

   Albern, Nicole; Voigt, Aiko; Thompson, David W.; Pinto, Joaquim G. (September 2020, Journal of Climate)

   null (Ed.)

   Abstract Previous studies showed that global cloud-radiative changes contribute half or more to the midlatitude atmospheric circulation response to global warming. Here, we investigate the relative importance of tropical, midlatitude, and polar cloud-radiative changes for the annual-mean, wintertime, and summertime circulation response across regions in AMIP-like simulations. To this end, we study global warming simulations from the ICON model run with the cloud-locking method and prescribed sea surface temperatures, which isolate the impact of changes in atmospheric cloud-radiative heating. Tropical cloud changes dominate the global cloud impact on the 850 hPa zonal wind, jet strength, and storm track responses across most seasons and regions. For the jet shift, a more diverse picture is found. In the annual mean and DJF, tropical and midlatitude cloud changes contribute substantially to the poleward jet shift in all regions. The poleward jet shift is further supported by polar cloud changes across the Northern Hemisphere but not in the Southern Hemisphere. In JJA, the impact of regional cloud changes on the jet position is small, consistent with an overall small jet shift during this season. The jet shift can be largely understood via the anomalous atmospheric cloud-radiative heating in the tropical and midlatitude upper troposphere. The circulation changes are broadly consistent with the influence of cloud-radiative changes on upper-tropospheric baroclinicity and thus the mean potential energy available for conversion into eddy kinetic energy. Our results help to explain the jet response to global warming and highlight the importance of tropical and midlatitude cloud-radiative changes for this response. 

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4. A Process Model for ITCZ Narrowing under Warming Highlights Clear-Sky Water Vapor Feedbacks and Gross Moist Stability Changes in AMIP Models

   https://doi.org/10.1175/JCLI-D-22-0689.1  

   Ahmed, Fiaz; Neelin, J. David; Hill, Spencer A.; Schiro, Kathleen A.; Su, Hui (August 2023, Journal of Climate)

   Abstract Tropical areas with mean upward motion—and as such the zonal-mean intertropical convergence zone (ITCZ)—are projected to contract under global warming. To understand this process, a simple model based on dry static energy and moisture equations is introduced for zonally symmetric overturning driven by sea surface temperature (SST). Processes governing ascent area fraction and zonal mean precipitation are examined for insight into Atmospheric Model Intercomparison Project (AMIP) simulations. Bulk parameters governing radiative feedbacks and moist static energy transport in the simple model are estimated from the AMIP ensemble. Uniform warming in the simple model produces ascent area contraction and precipitation intensification—similar to observations and climate models. Contributing effects include stronger water vapor radiative feedbacks, weaker cloud-radiative feedbacks, stronger convection-circulation feedbacks, and greater poleward moisture export. The simple model identifies parameters consequential for the inter-AMIP-model spread; an ensemble generated by perturbing parameters governing shortwave water vapor feedbacks and gross moist stability changes under warming tracks inter-AMIP-model variations with a correlation coefficient ∼0.46. The simple model also predicts the multimodel mean changes in tropical ascent area and precipitation with reasonable accuracy. Furthermore, the simple model reproduces relationships among ascent area precipitation, ascent strength, and ascent area fraction observed in AMIP models. A substantial portion of the inter-AMIP-model spread is traced to the spread in how moist static energy and vertical velocity profiles change under warming, which in turn impact the gross moist stability in deep convective regions—highlighting the need for observational constraints on these quantities. Significance Statement A large rainband straddles Earth’s tropics. Most, but not all, climate models predict that this rainband will shrink under global warming; a few models predict an expansion of the rainband. To mitigate some of this uncertainty among climate models, we build a simpler model that only contains the essential physics of rainband narrowing. We find several interconnected processes that are important. For climate models, the most important process is the efficiency with which clouds move heat and humidity out of rainy regions. This efficiency varies among climate models and appears to be a primary reason for why climate models do not agree on the rate of rainband narrowing. 

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5. The Response of Tropical Cyclone Inner Core and Outer Rainband Precipitation to Warming in Idealized Convection‐Permitting WRF

   https://doi.org/10.1029/2024JD042217  

   Stansfield, Alyssa M; Rasmussen, Kristen L (February 2025, Journal of Geophysical Research: Atmospheres)

   Abstract Global mean and extreme tropical cyclone (TC) precipitation have been increasing over the past few decades and are expected to continue to increase into the future due to climate change. Most projections of future TC precipitation use climate models with grid spacings of 25–100 km, which are too coarse to resolve the convective structures and small‐scale precipitation processes within TCs. This work uses convection‐permitting Weather Research and Forecasting model simulations to investigate how precipitation and precipitation processes change in the inner core (IC) and outer rainbands (OR) of TCs in response to sea surface temperature (SST) warming. The simulations are idealized, with single TCs initialized from weak vortices over domain‐constant SSTs. In these simulations, TC intensity and IC precipitation greatly increase with SST warming while OR precipitation increases slightly. A greater area in the IC is occupied by deep convection more frequently in the warmer simulations, while the deep convective activity remains relatively constant with warming in the TC OR. Mixing ratios of hydrometeors and cloud ice increase with warming in both the IC and OR, while the TCs' vertical circulations deepen, melting levels rise, and mean upward velocities strengthen. This work demonstrates how analysis of three‐dimensional storm structures can provide insight into processes that change TC precipitation in different regions of the storm, and future work will include applying this analysis to more realistic convection‐permitting simulations. 

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