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The Tibetan Plateau (TP) exerts significant influences on Earth's climate, and it is commonly accepted that the plateau enhances the intensity of the Asian summer monsoon (ASM). However, since the TP is located in the subtropics and its climate responses consist of both tropical and extratropical characteristics, a natural question to ask is how the TP would affect the ASM if it were shifted to different latitudes. A series of experiments with a state-of-the-art Earth system model demonstrates that the current location of the TP is not optimal for intensifying the ASM. When the TP is moved southward, the tropical South Asian monsoon (SAM) intensifies, associated with strengthened thermally driven atmospheric circulation, while the subtropical East Asian monsoon (EAM) weakens. When the TP is located in higher-than-current latitudes, on the other hand, the SAM weakens and the EAM intensifies. In particular, when the TP shifts northward by 8° of latitude, the Asian continent witnesses the heaviest summer monsoon rainfall. Changes in the meridional location of the plateau cause substantial differences in atmospheric circulation and water vapor transport, and thus in monsoon rainfall. Significance Statement: The existence of the Tibetan Plateau (TP) enhances the Asian summer monsoon; however, the optimal positions of the TP for affecting the monsoon and its various components are unknown. This study shows that the different TP locations exert different influences on the monsoon. When the TP is shifted southward, the South Asian monsoon intensifies while the East and Southeast Asian monsoons weaken. When the TP is shifted northward, the South Asian monsoon weakens constantly while the East and Southeast Asian monsoons strengthen before they become weaker when the plateau is shifted by 12° of latitude. Much of the Asian continent would witness the heaviest monsoon rainfall when the TP is shifted northward by 8° of latitude. [ABSTRACT FROM AUTHOR]

The Maritime Continent (MC) is regarded as an important heat source region and the impact of MC heating on the West Antarctic climate which is largely controlled by the Amundsen Sea Low (ASL) is unknown. This study is focused on the impact of intensified convective heating over the MC on the variation of the ASL in the austral fall. It is observed that enhanced MC heating is linked to deepening of the eastern ASL, a feature reproduced successfully by a model experiment in which additional heating is introduced to the MC. The intensified MC heating generates anticyclonic anomalies that result in a Rossby wave source in the upper troposphere to the south of MC. Then the Rossby wave originated from the new source propagates southeastward and deepens the eastern ASL. Additional model experiments prove that the response of ASL to MC heating is stronger than that to central Pacific cooling. Plain Language Summary: West Antarctica has experienced the strongest atmospheric warming in the Southern Hemisphere and the atmospheric circulation here is largely controlled by the Amundsen Sea Low (ASL) that resides along most of the western Antarctic Peninsula coast. Tropical heating is important for modulating the variations of ASL but the complicated mechanism between the tropics and the Antarctica is still unclear. Recent studies found that the atmospheric circulation over West Antarctica is affected by anomalous heating over the central Pacific (CP) that usually occurs simultaneously with the heating over the Maritime Continent (MC), and the impact of the MC heating on West Antarctic climate is unknown. This study is focused on the impact of intensified heating over the MC on the variation of ASL in austral fall. Both observations and model experiments prove that MC heating influences the ASL through Rossby wave trains while the CP cooling exerts an impact on the ASL through the westerly jet stream. The response of ASL to MC heating is stronger than that to CP cooling in austral fall in model simulations. This study enhances our understanding of how tropical heatings in different locations influence the West Antarctic climate. Key Points: Maritime Continent (MC) variability replaces the dominant role of central Pacific (CP) variability in modulating the variations of Amundsen Sea Low (ASL) in March‐April‐MayMC heating influences the ASL through Rossby wave trains while the CP cooling exerts an impact on the ASL through the westerly jet streamThe response of ASL to MC heating is stronger than that to CP cooling [ABSTRACT FROM AUTHOR]

Atmospheric diabatic heating, a major driving force of atmospheric circulation over the tropics, is strongly confined to the tropical western North Pacific (TWNP) region, with the global warmest sea surface temperature (SST). The changes in diabatic heating over the TWNP, which exert great impacts on the global climate system, have recently exhibited a noticeable seasonal dependence with a remarkable increase in boreal spring. In this study, we applied observations, reanalysis data, and numerical experiments to investigate the causes of the seasonality in heating changes. Results show that in boreal spring convection is more sensitive to the TWNP SST, leading to a more significant enhancement of deep convection, although the increase in the SST is nearly the same as that in the other seasons. In the non-spring seasons, the enhanced convection due to increased local SST is suppressed by the anomalous anticyclonic wind shear over the TWNP, generated by the easterly wind anomalies induced by the tropical Indian Ocean (TIO) warming via the Kevin waves. However, the TIO warming does not show any suppressing effect in spring because it is much weaker than that in the other seasons and thus the warming itself cannot induce sufficient convective heating anomalies to excite the Kelvin waves. [ABSTRACT FROM AUTHOR]

This study examines the climate response to a sea surface temperature (SST) warming imposed over the southwest tropical Indian Ocean (TIO) in a coupled ocean–atmosphere model. The results indicate that the southwest TIO SST warming can remotely modulate the atmospheric circulation over the western North Pacific Ocean (WNP) via interbasin air–sea interaction during early boreal summer. The southwest TIO SST warming induces a "C shaped" wind response with northeasterly and northwesterly anomalies over the north and south TIO, respectively. The northeasterly wind anomalies contribute to the north TIO SST warming via a positive wind–evaporation–SST (WES) feedback after the Asian summer monsoon onset. In June, the easterly wind response extends into the WNP, inducing an SST cooling by WES feedback on the background trade winds. Both the north TIO SST warming and the WNP SST cooling contribute to an anomalous anticyclonic circulation (AAC) over the WNP. The north TIO SST warming, WNP SST cooling, and AAC constitute an interbasin coupled mode called the Indo-western Pacific Ocean capacitor (IPOC), and the southwest TIO SST warming could be a trigger for IPOC. While the summertime southwest TIO SST warming is often associated with antecedent El Niño, the warming in 2020 seems to be related to extreme Indian Ocean dipole during the autumn of 2019. The strong southwest TIO SST warming seems to partly explain the strong summer AAC of 2020 over the WNP even without a strong antecedent El Niño. [ABSTRACT FROM AUTHOR]

Changes in the tropical atmospheric overturning circulation can strongly influence the global weather pattern via affecting the location, extent, and strength of tropical convective heating. However, due to limitations in obtaining reliable global data before the satellite era, there are still uncertainties on long‐term changes in the tropical overturning features, such as the Walker Circulation. By analysing the 20th century reanalysis products, ship‐based observations and gauge‐based land precipitation data, robust intensification of convection is found over the western equatorial Pacific and Maritime Continent (WEP‐MC; 90°E–150°E/15°S–15°N), where rainfall and total cloud cover increased by 15–20% in boreal spring during 1901–2010. The signal is noticeably seasonally dependent, and both rainfall and cloud cover show consistent and significant increasing trends only in the boreal spring season. General circulation model (GCM) experiments were conducted using two different reconstructed SST data sets as forcing; results from both runs indicate springtime intensification of WEP‐MC convection, even with relatively uniform SST warming. Further, numerical experiments using a simplified model show that the Pacific trade wind can be accelerated by intensifying cumulus heating; however, this can be sensitive to the location of convection, and only occurs if the latter is within ±5° in latitude along the equator. Our findings suggest that the secular change in the Walker Circulation is potentially discovered from the current reanalysis and observational data sets if "regional‐up" approaches are applied. [ABSTRACT FROM AUTHOR]

In January of 2016, the Ross Sea sector of the West Antarctica ice sheet experienced a 3‐week‐long melting episode. Here we quantify the association of the large‐extent and long‐lasting melting event with the enhancement of the downward longwave (LW) radiative fluxes at surface due to water vapor, cloud, and atmospheric dynamic feedbacks using the ERA‐Interim data set. The abnormally long‐lasting temporal surges of atmospheric moisture, warm air, and low‐level clouds increase the downward LW radiative energy flux at the surface during the massive ice‐melting period. The concurrent timing and spatial overlap between poleward wind anomalies and positive downward LW radiative surface energy flux anomalies over West Antarctica due to warmer air temperature and increases in atmospheric water vapor and cloud coverage provide direct evidence that warm and moist air advection from lower latitudes to West Antarctica causes the rapid long‐lasting warming and vast ice mass loss in January of 2016. Plain Language Summary: The melting of the fringing ice shelves from below by warm ocean water is thought to be the leading factor responsible for the retreat of the West Antarctica ice sheet in the past several decades. The analysis presented here shows that atmospheric processes through the long‐range transport of heat and moisture from lower latitudes to West Antarctica by the atmospheric circulation can lead to temporal surges of downward longwave radiative fluxes at the surface, substantially warming the surface. Atmospheric poleward heat transport plays a key role for individual ice sheet melting events in West Antarctica, such as the ice sheet melting episode over Ross Sea sector of the West Antarctica Ice Sheet in January 2016. Key Points: Pronounced enhancement of downward longwave radiative energy fluxes results in massive melting of the West Antarctica Ice Sheet in January 2016Contributions to the enhancement of downward longwave radiative fluxes are quantified via a linearized radiative transfer modelAtmospheric poleward heat transport plays a key role for the enhancement of downward longwave radiative surface energy fluxes [ABSTRACT FROM AUTHOR]

The South China Sea (SCS) summer monsoon onset has been regarded as the beginning of the East Asian summer monsoon. In this study, we investigated the impacts of the SCS monsoon onset on the transition from the spring persistent rainfall to the summer Meiyu in the middle and lower reaches of the Yangtze River basin (MLYZB). It is found that rainfall in the MLYZB reduces after the SCS monsoon onset. This reduction in rainfall persists until the onset of the Meiyu and is accompanied by a weakening of southwesterlies to the south of the MLYZB. These features exist in both climatology and interannual variability. Rainfall increases significantly over the SCS and the subtropical western North Pacific after the SCS monsoon onset. The latent heating of the increased rainfall can excite an anomalous cyclone over the western North Pacific, which weakens the mean southwesterlies to the south of the MLYZB and decreases water vapor entering the MLYZB. It also generates descending motion over southeastern China. Thus, the SCS monsoon onset could suppress rainfall over the MLYZB by the latent heating induced changes in circulation. Compared to increased rainfall over the SCS, the latent heating of increase rainfall over the subtropical western North Pacific plays a more important role in the reduction of rainfall over the MLYZB. As the SCS monsoon onset affects the timing of the reduction of rainfall in the MLYZB, an early SCS monsoon onset is accompanied by below-normal May rainfall in the MLYZB, while a late SCS monsoon onset is accompanied by above-normal May rainfall. [ABSTRACT FROM AUTHOR]