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Spring tripole sea surface temperature (SST) anomalies over the North Atlantic are an outstanding regional mode of interannual climate variability in association with spring North Atlantic Oscillation. Based on the observed and reanalyzed datasets during 1960–2020, this study investigates the relationship between the spring tripole North Atlantic SST (TNAT) anomalies and the following peak summer (July–August) western North Pacific subtropical high (WNPSH). The results show that the ‘+ − +’ TNAT anomalies in spring could induce a strengthened WNPSH in the following peak summer. However, such a climatic effect of spring TNAT anomalies on WNPSH is unstable, exhibiting an evident interdecadal strengthening since the middle 1990s. This is due to a strengthened intensity of spring TNAT anomalies in recent decades. Compared to the early epoch (1960–1995), stronger spring TNAT anomalies in the post epoch (1996–2020) could cause a stronger pan-tropical climate response until the following peak summer through a series of ocean–atmosphere interactions, with the prominent cooling over the central Pacific and warming over the Maritime Continent in response to the ‘+ − +’ TNAT anomalies. This helps maintain an anomalous anticyclone over the Northwest Pacific via the Walker circulation adjustment and Rossby wave response. As a result, the WNPSH is significantly enhanced since the middle 1990s. By contrast, in the early epoch, spring TNAT anomalies are relatively weaker, inducing weaker pan-tropical ocean–atmosphere interactions and thus less change in the WNPSH. Our results highlight a strengthened lagged effect of spring TNAT anomalies on the following peak summer WNPSH.

Global models comprising the sixth-generation Coupled Climate Model Intercomparison Project (CMIP6) are downscaled using a very high-resolution but simplified coupled atmosphere–ocean tropical cyclone model, as a means of estimating the response of global tropical cyclone activity to increasing greenhouse gases. As with a previous downscaling of CMIP5 models, the results show an increase in both the frequency and severity of tropical cyclones, robust across the models downscaled, in response to increasing greenhouse gases. The increase is strongly weighted to the Northern Hemisphere, and especially noteworthy is a large increase in the higher latitudes of the North Atlantic. Changes are insignificant in the South Pacific across metrics. Although the largest increases in track density are far from land, substantial increases in global landfalling power dissipation are indicated. The incidence of rapid intensification increases rapidly with warming, as predicted by existing theory. Measures of robustness across downscaled climate models are presented, and comparisons to tropical cyclones explicitly simulated in climate models are discussed.

The summer Asian westerly jet (AWJ)’s shifting in latitudes is one important characteristic of its variability and has great impact on the East Asian summer climate. Based on the observed and reanalyzed datasets from the Hadley Center Sea Ice and Sea Surface Temperature dataset (HadISST), the Japanese 55-year reanalysis (JRA-55), and the fifth generation of the European Centre for Medium-Range Weather Forecasts atmospheric reanalysis (ERA5), this study investigates the relationship between the spring tripole North Atlantic SST (TNAT) anomalies and the summer meridional shift of the AWJ (MSJ) for the period of 1958–2020. Through the method of correlation analysis and regression analysis, we show that the ‘+ - +’ TNAT anomalies in spring could induce a northward shift of the AWJ in the following summer. However, such a climatic effect of the spring TNAT anomalies on the MSJ is unstable, exhibiting an evident interdecadal strengthening since the early 1990s. Further analysis reveals that this is related to a strengthened intensity of the spring TNAT anomalies in the most recent three decades. Compared to the early epoch (1958–1993), the stronger spring TNAT anomalies in the post epoch (1994–2020) could cause a stronger pan-tropical climate response until the following summer through a series of ocean–atmosphere interactions. Through Gill responses, the resultant more prominent cooling in the central Pacific in response to the ‘+ - +’ TNAT anomalies induces a pan-tropical cooling in the upper troposphere, which weakens the poleward gradient of the tropospheric temperature over subtropical Asia. As a result, the AWJ shifts northward via a thermal wind effect. By contrast, in the early epoch, the spring TNAT anomalies are relatively weaker, inducing weaker pan-tropical ocean–atmosphere interactions and thus less change in the meridional shit of the summer AWJ. Our results highlight a strengthened lagged effect of the spring TNAT anomalies on the following summer MSJ and have important implications for the seasonal climate predictability over Asia.

Atmospheric rivers (ARs), tropical storms (TSs), and mesoscale convective systems (MCSs) are important weather phenomena that often threaten society through heavy precipitation and strong winds. Despite their potentially vital role in global and regional hydrological cycles, their contributions to long-term mean and extreme precipitation have not been systematically explored at the global scale. Using observational and reanalysis data, and NOAA’s Geophysical Fluid Dynamics Laboratory’s new high-resolution global climate model, we quantify that despite their occasional (13%) occurrence globally, AR, TS, and MCS days together account for ∼55% of global mean precipitation and ∼75% of extreme precipitation with daily rates exceeding its local 99th percentile. The model reproduces well the observed percentage of mean and extreme precipitation associated with AR, TS, and MCS days. In an idealized global warming simulation with a homogeneous SST increase of 4 K, the modeled changes in global mean and regional distribution of precipitation correspond well with changes in AR/TS/MCS precipitation. Globally, the frequency of AR days increases and migrates toward higher latitudes while the frequency of TS days increases over the central Pacific and part of the south Indian Ocean with a decrease elsewhere. The frequency of MCS days tends to increase over parts of the equatorial western and eastern Pacific warm pools and high latitudes and decreases over most part of the tropics and subtropics. The AR/TS/MCS mean precipitation intensity increases by ∼5% K−1 due primarily to precipitation increases in the top 25% of AR/TS/MCS days with the heaviest precipitation, which are dominated by the thermodynamic component with the dynamic and microphysical components playing a secondary role.

The record-breaking mei-yu in the Yangtze-Huaihe River valley (YHRV) in 2020 was characterized by an early onset, a delayed retreat, a long duration, a wide meridional rainbelt, abundant precipitation, and frequent heavy rainstorm processes. It is noted that the East Asian monsoon circulation system presented a significant quasi-biweekly oscillation (QBWO) during the mei-yu season of 2020 that was associated with the onset and retreat of mei-yu, a northward shift and stagnation of the rainbelt, and the occurrence and persistence of heavy rainstorm processes. Correspondingly, during the mei-yu season, the monsoon circulation subsystems, including the western Pacific subtropical high (WPSH), the upper-level East Asian westerly jet, and the low-level southwesterly jet, experienced periodic oscillations linked with the QBWO. Most notably, the repeated establishment of a large southerly center, with relatively stable latitude, led to moisture convergence and ascent which was observed to develop repeatedly. This was accompanied by a long-term duration of the mei-yu rainfall in the YHRV and frequent occurrences of rainstorm processes. Moreover, two blocking highs were present in the middle to high latitudes over Eurasia, and a trough along the East Asian coast was also active, which allowed cold air intrusions to move southward through the northwestern and/or northeastern paths. The cold air frequently merged with the warm and moist air from the low latitudes resulting in low-level convergence over the YHRV. The persistent warming in the tropical Indian Ocean is found to be an important external contributor to an EAP/PJ-like teleconnection pattern over East Asia along with an intensified and southerly displaced WPSH, which was observed to be favorable for excessive rainfall over YHRV.

Southern Hemispheric (SH) sudden stratospheric warmings (SSWs) are relatively rare compared to their Northern Hemisphere counterparts. No study has so far investigated the impacts of the SH minor SSWs on the tropical atmosphere and connection between the tropical and polar atmospheres. Here, we analyze the MERRA‐2 and ERA‐interim datasets, and Microwave Limb Sounder satellite temperature measurements to investigate the tropical and polar atmosphere tele‐connections during the SH minor SSW that occurred in 2010. Our analysis shows the strong anti‐correlation between the polar and tropical temperatures during the 2010 minor SSW in the stratosphere and mesosphere. This is the first observational study over the SH that reveals the tele‐connection between the tropical and polar middle atmospheres through the temperature during a minor SSW. We verified this tele‐connection, using simulations of the Ground‐to‐topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) model during the 2010 minor SSW. GAIA model simulations show the temperature anti‐correlation between the tropical and polar middle atmosphere and zonal wind variations. The feature of meridional circulation changes was also observed during the SSW period. Hence, the present study strongly suggests that even minor SSW in the SH can affect the meridional circulation in the middle atmosphere via planetary wave activity.

The Radiative‐Convective Equilibrium Model Intercomparison Project (RCEMIP) is an intercomparison of multiple types of numerical models configured in radiative‐convective equilibrium (RCE). RCE is an idealization of the tropical atmosphere that has long been used to study basic questions in climate science. Here, we employ RCE to investigate the role that clouds and convective activity play in determining cloud feedbacks, climate sensitivity, the state of convective aggregation, and the equilibrium climate. RCEMIP is unique among intercomparisons in its inclusion of a wide range of model types, including atmospheric general circulation models (GCMs), single column models (SCMs), cloud‐resolving models (CRMs), large eddy simulations (LES), and global cloud‐resolving models (GCRMs). The first results are presented from the RCEMIP ensemble of more than 30 models. While there are large differences across the RCEMIP ensemble in the representation of mean profiles of temperature, humidity, and cloudiness, in a majority of models anvil clouds rise, warm, and decrease in area coverage in response to an increase in sea surface temperature (SST). Nearly all models exhibit self‐aggregation in large domains and agree that self‐aggregation acts to dry and warm the troposphere, reduce high cloudiness, and increase cooling to space. The degree of self‐aggregation exhibits no clear tendency with warming. There is a wide range of climate sensitivities, but models with parameterized convection tend to have lower climate sensitivities than models with explicit convection. In models with parameterized convection, aggregated simulations have lower climate sensitivities than unaggregated simulations. Plain Language Summary This study investigates tropical clouds and climate using results from more than 30 different numerical models set up in a simplified framework. The data set of model simulations is unique in that it includes a wide range of model types configured in a consistent manner. We address some of the biggest open questions in climate science, including how cloud properties change with warming and the role that the tendency of clouds to form clusters plays in determining the average climate and how climate changes. While there are large differences in how the different models simulate average temperature, humidity, and cloudiness, in a majority of models, the amount of high clouds decreases as climate warms. Nearly all models simulate a tendency for clouds to cluster together. There is agreement that when the clouds are clustered, the atmosphere is drier with fewer clouds overall. We do not find a conclusive result for how cloud clustering changes as the climate warms. Key Points Temperature, humidity, and clouds in radiative‐convective equilibrium vary substantially across models Models agree that self‐aggregation dries the atmosphere and reduces high cloudiness There is no consistency in how self‐aggregation depends on warming

Extreme heat under global warming is a concerning issue for the growing tropical population. However, model projections of extreme temperatures, a widely used metric for extreme heat, are uncertain on regional scales. In addition, humidity needs to be taken into account to estimate the health impact of extreme heat. Here we show that an integrated temperature–humidity metric for the health impact of heat, namely, the extreme wet-bulb temperature (TW), is controlled by established atmospheric dynamics and thus can be robustly projected on regional scales. For each 1 °C of tropical mean warming, global climate models project extreme TW (the annual maximum of daily mean or 3-hourly values) to increase roughly uniformly between 20° S and 20° N latitude by about 1 °C. This projection is consistent with theoretical expectation based on tropical atmospheric dynamics, and observations over the past 40 years, which gives confidence to the model projection. For a 1.5 °C warmer world, the probable (66% confidence interval) increase of regional extreme TW is projected to be 1.33–1.49 °C, whereas the uncertainty of projected extreme temperatures is 3.7 times as large. These results suggest that limiting global warming to 1.5 °C will prevent most of the tropics from reaching a TW of 35 °C, the limit of human adaptation. Limiting global warming to 1.5 °C will prevent tropical regions from reaching the limit of human adaptability, according to robust dynamical constraints on projected heat stress.

Despite substantial global mean warming, surface cooling has occurred in both the tropical eastern Pacific Ocean and the Southern Ocean over the past 40 years, influencing both regional climates and estimates of Earth’s climate sensitivity to rising greenhouse gases. While a tropical influence on the extratropics has been extensively studied in the literature, here we demonstrate that the teleconnection works in the other direction as well, with the southeast Pacific sector of the Southern Ocean exerting a strong influence on the tropical eastern Pacific. Using a slab ocean model, we find that the tropical Pacific sea surface temperature (SST) response to an imposed Southern Ocean surface heat flux forcing is sensitive to the longitudinal location of that forcing, suggesting an atmospheric pathway associated with regional dynamics rather than reflecting a zonal-mean energetic constraint. The transient response shows that an imposed Southern Ocean cooling in the southeast Pacific sector first propagates into the tropics by mean-wind advection. Once tropical Pacific SSTs are perturbed, they then drive remote changes to atmospheric circulation in the extratropics that further enhance both Southern Ocean and tropical cooling. These results suggest a mutually interactive two-way teleconnection between the Southern Ocean and tropical Pacific through atmospheric circulations, and highlight potential impacts on the tropics from the extratropical climate changes over the instrumental record and in the future.

Errors of coupled general circulation models (CGCMs) limit their utility for climate prediction and projection. Origins of and feedback for tropical biases are investigated in the historical climate simulations of 18 CGCMs from phase 5 of the Coupled Model Intercomparison Project (CMIP5), together with the available Atmospheric Model Intercomparison Project (AMIP) simulations. Based on an intermodel empirical orthogonal function (EOF) analysis of tropical Pacific precipitation, the excessive equatorial Pacific cold tongue and double intertropical convergence zone (ITCZ) stand out as the most prominent errors of the current generation of CGCMs. The comparison of CMIP–AMIP pairs enables us to identify whether a given type of errors originates from atmospheric models. The equatorial Pacific cold tongue bias is associated with deficient precipitation and surface easterly wind biases in the western half of the basin in CGCMs, but these errors are absent in atmosphere-only models, indicating that the errors arise from the interaction with the ocean via Bjerknes feedback. For the double ITCZ problem, excessive precipitation south of the equator correlates well with excessive downward solar radiation in the Southern Hemisphere (SH) midlatitudes, an error traced back to atmospheric model simulations of cloud during austral spring and summer. This extratropical forcing of the ITCZ displacements is mediated by tropical ocean–atmosphere interaction and is consistent with recent studies of ocean–atmospheric energy transport balance.