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Under global warming, the convective heating over the western Pacific (WP) has exhibited a significantly intensifying trend during the boreal spring, while the surface air temperatures in the Middle East (ME) have increased more rapidly than those in other tropical regions. Are these climate phenomena of the two regions physically connected? If yes, what are the responsible dynamical mechanisms involved? Utilizing the ERA5 reanalysis data and model simulations, this study reveals a significant seesaw variation in the convection and temperature trends between WP and ME. When convective heating intensifies over the WP, the ME tends to be drier and hotter during the spring, and vice versa. A further investigation indicates that the enhanced WP convective heating can induce anticyclonic circulation anomalies in the upper and middle troposphere over the Iranian and Tibetan plateaus. These anomalous high pressures extend westward, exhibiting a barotropic structure, which leads to stronger sinking motions, reduced cloud cover, and increased surface solar radiation over the ME. Consequently, these conditions result in drier and hotter soils and an increase in heatwave days in the ME. This study provides useful information for enhancing our understanding of the role of tropical WP climate change in influencing the upstream climate conditions with a focus on the ME. Plain Language Summary: Under global warming, the western Pacific (WP) has experienced a significant increase in convective heating during the spring, while the Middle East (ME) is seeing a faster rise in surface temperatures compared to other tropical regions. This study investigates whether these climate changes in WP and ME are interconnected and what mechanisms may be involved. The results show that when convective heating intensifies over the WP, the ME tends to become drier and hotter in the spring. The findings suggest that increased heating over the WP can lead to anomalous high pressures over the Iranian and Tibetan plateaus, which result in reduced precipitation, decreased cloud cover, and increased solar radiation, causing higher temperatures in the ME. This study enhances our understanding of how climate changes in the tropical WP can influence weather and climate conditions in the ME. Key Points: The convection in the western Pacific (WP) has been intensifying during spring in 1979–2022Surface air temperatures have been rising faster in the Middle East (ME) than in other tropical regionsThe intensified WP convection likely contributes to the increase in heatwave days over the ME [ABSTRACT FROM AUTHOR]

The changes in the intensity of the southern tropical Indian Ocean dipole mode (STIOD) are investigated using observations and the Community Earth System Model Large Ensemble (CESM-LE) project in this study. The positive STIOD is characterized as cold SST anomalies over the tropical southeastern Indian Ocean (SEIO) and warm SST anomalies over the southcentral Indian Ocean (SCIO), which peak in boreal summer. It is suggested that the intensity of interannual variability in the STIOD experienced prominent interdecadal changes from 1970 to the present. The STIOD was relatively weak before the late 1980s, while it is enhanced significantly during the late 1980s to early-2000s and displayed some decrease in the intensity after the early-2000s. As an important generation mechanism, changes in the strengths of the Bjerknes feedback between the SCIO and SEIO mainly contribute to the variations of the STIOD intensity. The changes in Bjerknes feedback are associated with the variations in climatological mean states over the tropical Indian Ocean. The warmer climatological SST strengthens the efficiency of the SEIO SST in driving wind. On the other hand, the combined effects of the Indonesian Throughflow and surface climatological zonal winds alter the mean thermocline depth over the SEIO, contributing to the variations in the relationship between the thermocline depth and SST anomalies in situ. Two sets of historical and RCP8.5 simulations from CESM1-LE with 35 ensemble members are analyzed to confirm the roles of mean state changes on the intensity of interannual variability of STIOD. [ABSTRACT FROM AUTHOR]

An unprecedented marine heatwave (MHW) event occurred in the middle-high latitudes of the western North Pacific during the summer of 2022. We demonstrate that excessive precipitation thousands of kilometers away fuels this extreme MHW event in July 2022. In the upper atmosphere, a persistent atmospheric blocking system, forming over the MHW region, reduces cloud cover and increases shortwave radiation at the ocean surface, leading to high sea surface temperatures. Atmospheric perturbations induced by latent heat release from the extreme precipitation in the Indian summer monsoon region enhance this atmospheric blocking through the propagation of quasi-stationary Rossby waves. Our hypothesis is verified by using a numerical model that is forced with the observed atmospheric anomalous diabatic heating. This study sheds light on how a subtropical extreme event can fuel another extreme event at middle-high latitudes through an atmospheric teleconnection. [ABSTRACT FROM AUTHOR]

The Indian Ocean Basin (IOB) mode is believed to favor the decay of El Niño via modulating the zonal wind anomalies in the western equatorial Pacific, while the contribution of the Indian Ocean Dipole (IOD) mode to the following year's El Niño remains highly controversial. In this study, we use the evolution of fast and slow decaying El Niño events during 1950–2020 to demonstrate that the positive IOD with a strong western pole prompts the termination of El Niño, whereas a weak western pole has no significant effect. The strong western pole of a positive IOD leads to a strong IOB pattern peaking in the late winter (earlier than normal), enhancing local convection and causing anomalous rising motions over the tropical Indian Ocean and sinking motions over the western tropical Pacific. The surface equatorial easterly wind anomalies on the western flank of the sinking motions stimulate oceanic equatorial upwelling Kelvin waves, which shoal the thermocline in the eastern equatorial Pacific and rapidly terminate the equatorial warming during El Niño. However, a weak western pole of the IOD induces a weak IOB mode that peaks in the late spring, and the above-mentioned cross-basin physical processes do not occur. [ABSTRACT FROM AUTHOR]

The seasonal phase-locking feature of the Indian Ocean Dipole (IOD) is well documented. However, the seasonality tendency of sea surface temperature anomalies (SSTAs) during the development of the IOD has not been widely investigated. The SSTA tendencies over the two centers of the IOD peak in September-October-November are of different monthly amplitudes. The SSTA tendency over the west pole is small before June–July–August but dramatically increases in July–August–September. Meanwhile, the SSTA tendency over the east pole gradually increases before June-July-August and decreases since then. The growth rate attribution of the SSTAs is achieved by examining the roles of radiative and non-radiative air-sea coupled thermodynamic processes through the climate feedback-response analysis method (CFRAM). The CFRAM results indicate that oceanic dynamic processes largely contribute to the total SSTA tendency for initiating and fueling the IOD SSTAs, similar to previous studies. However, these results cannot explain the monthly amplitudes of SSTA tendency. Four negative feedback processes (cloud radiative feedback, atmospheric dynamic processes, surface sensible, and latent heat flux) together play a damping role opposite to the SSTA tendency. Nevertheless, the sea surface temperature-water vapor feedback shows positive feedback. Specifically, variations in SSTAs can change water vapor concentrations through evaporation, resulting in anomalous longwave radiation that amplifies the initial SSTAs through positive feedback. The effect of water vapor feedback is well in-phase with the monthly amplitudes of SSTA tendency, suggesting that the water vapor feedback might modulate the seasonally dependent SSTA tendency during the development of the IOD. [ABSTRACT FROM AUTHOR]

This study investigates the physical mechanisms responsible for the impacts of the Indian summer monsoon (ISM) on the evolution of El Niño–Southern Oscillation (ENSO), with a focus on understanding the monsoon-induced Pacific air–sea interactive processes. An observational analysis displays that a weaker-than-normal ISM can strengthen an ongoing El Niño event and weaken a La Niña event, and conversely for a stronger-than-normal ISM. A 1000-yr output from the Community Earth System Model version 2 is capable of reproducing this observed feature and is therefore used to explore the responsible ocean–atmosphere interactive processes involved. Results show that a weak ISM can cause a cyclonic circulation over the western North Pacific via stimulating atmospheric cold Kelvin waves, and conversely for a strong ISM. The westerly (easterly) wind anomalies on the southern flank of the anomalous cyclone (anticyclone) generate eastward (westward) current anomalies in the mixed layer and thus induce anomalous warm (cold) zonal advection. Furthermore, the wind anomalies excite oceanic downwelling (upwelling) Kelvin waves, which deepen (shoal) the thermocline in the equatorial eastern Pacific and result in anomalous warm (cold) vertical advection. A quantitative mixed layer heat budget analysis demonstrates that the influence of the monsoon-induced Pacific wind anomalies on ENSO is mainly achieved by changing the zonal advective feedback and thermocline feedback. This result is confirmed by model sensitivity experiments in which additional monsoon heating or cooling anomalies are imposed over the Indian region during the developing summer of an ENSO event. Significance Statement: While previous studies have reported that the Indian summer monsoon (ISM) could influence the evolution of El Niño–Southern Oscillation (ENSO), this study is aimed at understanding the physical mechanisms for the Pacific air–sea interactive processes induced by the monsoon and their impact on ENSO. It is found that a weak and strong ISM can respectively induce an anomalous cyclonic and anticyclonic circulation over the western North Pacific. The wind anomalies on the southern flank of the anomalous circulation mainly change the zonal advective feedback and the thermocline feedback to affect ENSO development. This study provides a detailed physical explanation of how the ISM influences ENSO evolution. [ABSTRACT FROM AUTHOR]

The Pacific Meridional Mode (PMM) plays a critical role in affecting El Niño‐Southern Oscillation (ENSO). This study examines the phase asymmetry of PMM events triggered by tropical and extratropical forcings, namely successive and stochastic events, respectively. It is shown that successive events exhibit negative asymmetry due to stronger trigger in the negative phase, while stochastic events display positive asymmetry due to stronger growth in the positive phase. The opposite phase asymmetry of two types of events respectively results in more frequent persistent La Niña events than El Niño events and more frequent episodic El Niño events than La Niña events, which increase ENSO transition complexity. This research provides a comprehensive understanding of PMM asymmetry and reconciles conflicting perspectives from previous studies. Additionally, the newly proposed contribution of positively asymmetric stochastic PMM events to more frequent episodic El Niño events in this study may enhance our comprehension of ENSO transition complexity. Plain Language Summary: In this study, we investigated the influences of the Pacific Meridional Mode (PMM), an important modulator of El Niño‐Southern Oscillation (ENSO), on the diverse transition preference of ENSO events (ENSO transition complexity). We first divided PMM events into two types that are respectively triggered by tropical and extratropical forcing, and named them as successive and stochastic PMM events. Successive PMM events tend to enhance persistency of ENSO events, whereas stochastic PMM events incline to initiate ENSO events from a neutral state. We found that the successive PMM events are negatively asymmetric because the triggering effect of tropical forcing is stronger in the negative phase. This negative asymmetry leads to longer persistency of La Niña events than El Niño events. On the contrary, the stochastic PMM events are positively asymmetric because the growth rate of PMM is stronger in the positive phase. This positive phase asymmetry of stochastic PMM events results in more frequent episodic El Niño events than La Niña events. This study is the first to show the contribution of positively asymmetric stochastic PMM events to higher frequency of episodic El Niño events, which may supplement our understanding of ENSO transition complexity. Key Points: Pacific Meridional Mode (PMM) events can be divided into tropical‐forced successive events and extratropical‐forced stochastic eventsSuccessive PMM events are negatively asymmetric, whereas stochastic ones are positively asymmetricOpposite asymmetry of two types of PMM events, respectively, is conducive to more frequent persistent La Niñas and episodic El Niños [ABSTRACT FROM AUTHOR]

Typhoons can cause massive casualties and economic damage, and accurately predicting typhoon intensity has always been a hot topic both in theory and practice. In consideration with the spatial and temporal complexity of typhoons, machine learning methods have recently been applied in typhoon forecasting. In this paper, we attempt to improve typhoon intensity forecasting by treating it as a spatio-temporal problem in the deep learning field. In particular, we propose a novel typhoon intensity forecasting model named the Typhoon Intensity Spatio-temporal Prediction Network (TITP-Net). The proposed model takes multidimensional environmental variables and physical factors of typhoons into account and fully extracts the information from the datasets by capturing spatio-temporal dependencies with a spatial attention module, which includes two-dimensional and three-dimensional convolutional operations. A series of experiments with a comprehensive framework by using TITP-Net are conducted. The MAEs of the forecasts with 18, 24, 36 and 48 h lead time obtain a significant improvement by 7.02%, 6.53%, 6.25% and 5.37% compared with some existing deep learning models and dynamical models from official agencies. [ABSTRACT FROM AUTHOR]

Climate models predict that East Asia (EA) will be substantially warmer than the present despite large inter-model uncertainty. This study investigated the major sources of the climate projections and the inter-model uncertainty. Particularly, we decomposed the differences in surface temperatures between the historical and RCP8.5 runs from 26 CMIP5 into partial surface temperature changes due to individual radiative and non-radiative processes through the climate feedback-response analysis method. Results show that anthropogenic greenhouse forcing and subsequent water vapor feedback processes are primarily responsible for the surface warming over EA. Relatively more rapid warming over the snow/ice-covered area and southern China is due to feedback processes associated with surface albedo and cloud, respectively. The regional warming is, however, compensated by the surface non-radiative (sensible and latent heat) cooling. The inter-model projection uncertainty is substantially large over high latitudes and the Tibetan Plateau mainly due to surface albedo feedback. Again, this large uncertainty is partly suppressed by surface non-radiative cooling. Water vapor and cloud feedbacks are the secondary important sources of the projection uncertainty. Moreover, the contributions of greenhouse forcing and atmospheric dynamics to the projection uncertainty are found to be minor. [ABSTRACT FROM AUTHOR]

This study investigates the mechanisms behind the Pacific meridional mode (PMM) in influencing the development of El Niño–Southern Oscillation (ENSO) events and their seasonal predictability. To examine the relative importance of various factors that may modulate the efficiency of the PMM influence, a series of experiments is conducted for selected ENSO events with different intensity using the Community Earth System Model, in which ensemble predictions are made from slightly different ocean initial states but under a common prescribed PMM surface heat flux forcing. Overall, a PMM forcing matched to ENSO—that is, a positive or negative PMM prior to an El Niño or a La Niña, respectively—plays an enhancing role, whereas a mismatched PMM forcing plays a damping role. For the matched cases, a positive PMM event enhances an El Niño more strongly than a negative PMM event enhances a La Niña. This asymmetry in influencing ENSO largely originates from the asymmetry in intensity between the positive and negative PMM events in the tropics, which can be explained by the nonlinearity in the growth and equatorward propagation of the PMM-related anomalies of sea surface temperature (SST) and surface zonal wind through both wind–evaporation–SST feedback and summer deep convection response. Our model results also indicate that the PMM acts as a modulator rather than a trigger for the occurrence of ENSO event. Furthermore, the response of ENSO to an imposed PMM forcing is modulated by the preconditioning of the upper-ocean heat content, which provides the memory for the coupled low-frequency evolution in the tropical Pacific Ocean. [ABSTRACT FROM AUTHOR]

Westerly wind bursts play an important role in the development of El Niño-Southern Oscillation (ENSO) events. However, the impact of easterly wind bursts (EWBs) on the development of ENSO is still unclear. In particular, a series of strong EWBs in the summer of 2014 aroused arguments about their importance in suppressing the potential warming in the summer. In this study, we conduct a series of sensitivity experiments using the fully-coupled NCAR Community Earth System Model with prescribed strong EWBs to distinguish their impact on the development of the model El Niño events, as well as the seasonality of the potential impact. Model results indicate that wintertime warming is significantly suppressed by the EWBs in summer due to the strongest ocean–atmosphere interaction associated with the most unstable background coupled system. With stronger anomalous zonal SST gradient and relatively more stable background state, the EWB-induced cooling in autumn is smaller than the cooling induced by the summertime EWBs. In spring when the ocean–atmosphere interaction is relatively weaker, the impact of EWBs depends on the EWB-forced shift of the eastern edge of warm pool (EEWP), which is critical for the establishment of positive Bjerknes feedback. A mixed layer heat budget analysis further suggests that the seasonally-dependent impact of EWBs is mainly controlled by the zonal advective feedback process associated with the subsequent ocean–atmosphere interaction and to some extent related to the thermocline feedback as well. This study demonstrates that EWBs increase the uncertainty of the prediction of ENSO initialized in boreal spring and early summer even if the ocean subsurface precursors are strong. [ABSTRACT FROM AUTHOR]

Model warming projections, forced by increasing greenhouse gases, have a large inter-model spread in both their geographical warming patterns and global mean values. The inter-model warming pattern spread (WPS) limits our ability to foresee the severity of regional impacts on nature and society. This paper focuses on uncovering the feedbacks responsible for the WPS. Here, we identify two dominant WPS modes whose global mean values also explain 98.7% of the global warming spread (GWS). We show that the ice-albedo feedback spread explains uncertainties in polar regions while the water vapor feedback spread explains uncertainties elsewhere. Other processes, including the cloud feedback, contribute less to the WPS as their spreads tend to cancel each other out in a model-dependent manner. Our findings suggest that the WPS and GWS could be significantly reduced by narrowing the inter-model spreads of ice-albedo and water vapor feedbacks, and better understanding the spatial coupling between feedbacks. The spatial pattern and global mean values of warming differ between different climate models, an issue that needs to be better understood in order to obtain reliable regional projections. Here, the authors show that ice-albedo and water vapor feedbacks are the key processes that are responsible for this inter-model spread. [ABSTRACT FROM AUTHOR]