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Using 51 models of the AMIP and historical experiments of CMIP6, we investigate the inter‐model diversity of atmospheric and coupled models in the strength of the Indian Summer Monsoon Rainfall (ISMR)–El Niño‐Southern Oscillation (ENSO) relationship. In atmospheric models, the Walker Circulation (WC) intensity associated with the western Pacific convective activity is most responsible for the inter‐model diversity. Models with strong WC have a strong ISMR–ENSO relationship via enhancing ENSO‐induced anomalies of the WC and monsoon circulation. The secondary source is the monsoon circulation differences associated with meridional rainfall contrast over the Indian monsoon region. In coupled models, the primary (secondary) source is the ENSO amplitude (WC intensity). In observation, the decadal variation of WC can also explain the changes in the ISMR–ENSO relationship. This study provides a basis for improving the model performance and advances our understanding of the observed ISMR–ENSO relationship changes. Plain Language Summary Numerical simulation using climate models is an important method in climate research. The Indian Summer Monsoon Rainfall (ISMR) prediction is based primarily on the El Niño‐Southern Oscillation (ENSO). However, the strength of the ISMR–ENSO relationship simulated by the current climate models is too diverse, which restricts the overall simulation and prediction of the ISMR by models. This study explores the main factors leading to the model diversity in the strength of the ISMR–ENSO relationship and finds that the simulated intensity of the mean state of the convective activity over the western Pacific is most responsible for the model diversity in the strength of the ISMR–ENSO relationship. Atmospheric models with more vigorous convection over the western Pacific tend to simulate a stronger ISMR–ENSO relationship. These results suggest that improving the simulation of the western Pacific convection in atmospheric models is key to improving the model performance for the ISMR–ENSO relationship simulation and ISMR prediction. Key Points In atmospheric models, the primary source of model diversity is the intensity of convective activity in the western Pacific The secondary source of atmospheric model diversity is the strength of monsoon circulation related to meridional rainfall contrast In coupled models, the primary (secondary) source of model diversity is the ENSO amplitude (Walker circulation)

The meridional teleconnection over East Asia (EA-MT) is one of the major features of East Asian summer monsoon (EASM), and it is also the important pathway for the impacts from both tropical and extratropical middle-high latitudes on the EASM. To reveal the temporal-spatial structure of summer EA-MT, multivariate EOF is applied to the latitude-pressure cross section of combined summer precipitation and zonal wind anomalies over East Asia, using GPCP precipitation and NCEP/NCAR reanalysis dataset during the period 1979–2016. Two leading modes of summer EA-MT are obtained and identified as the tropical and extratropical-origin EA-MT in terms of their specific characteristics and major sources, named “EA-TMT” and “EA-XTMT”, respectively. Both of them show strong interannual variabilities, and they demonstrate a quasi-barotropic structure of westerly wind anomalies that slightly tilts northward with height in the mid-high latitudes, and accordingly significant precipitation anomalies are constrained right underneath the anomalous zonal wind around the Yangtze River valley (YRV), which in turn helps to establish and maintain the summer EA-MT. The EA-TMT is triggered by anomalous convective activities in the western North Pacific and propagates northward in the mid-low troposphere, it has close relationship with the anomalies of East Asian summer westerly jet (EASWJ) intensity and the YRV precipitation, which is superior over the East Asia/Pacific and Pacific-Japan teleconnection patterns in representing the tropical-origin EA-MT. The EA-XTMT is however mainly initiated in the southeast of Kara Sea and propagating southeastward in the whole troposphere, it is dominated by the North Asian dipole mode and mainly related to the EASWJ position anomaly, favoring a “South Flood North Drought” pattern of precipitation anomalies over East China. Meanwhile, the EA-TMT is closely related to the summer SST anomalies in the tropical Pacific-Indian ocean and partly correlated with ENSO, whereas the EA-XTMT is possibly linked to the spring sea ice concentration anomalies in the western Arctic and Barents Sea. Furthermore, the joint contributions of EA-TMT and EA-XTMT are essential for the major variability of EASM, wherein the EA-TMT plays a primary role.

In this paper, the important role played by the local air-sea heat exchange in the east–west oscillation of the Western Pacific subtropical high (WPSH) on the sub-seasonal scale is revealed. First, the east–west oscillation index is defined for the WPSH using the relative vorticity field. The index can well characterize the sub-seasonal east–west oscillation of the WPSH, and it has a significant sub-seasonal cycle of 10–30 days. During the westward events, there is a cold sea surface temperature (SST) anomaly in the WPSH and its west side at the early stage of westward WPSH extension, and the cold SST anomaly makes the low-level atmosphere relatively stable, which is conducive to the generation of abnormal anticyclone, and then leads to the westward extension of the WPSH. During the westward WPSH extension, the convective activity is further suppressed; therefore, the water vapor evaporation and the cloud cover are reduced, and the net heat flux received by the ocean surface increases, eventually leading to the rise of SST. At the late stage of the westward extension, the continually enhanced warm SST causes instability of the low-level atmosphere, weakens the abnormal anticyclone, and then leads to the eastward retreat of the WPSH. Thereafter, the enhanced convective activities causes the increase of latent flux and cloud cover in the atmosphere, as well as the decrease of solar radiation flux. As a result, the warm SST anomaly weakens. The situation is the opposite for the eastward events. During the eastward or westward movement of the WPSH, beside the influence of the air-sea interaction in the WPSH region, the northward and northwestward propagation of the OLR anomaly in the tropical Indian Ocean and the Western Pacific respectively, and the SST anomaly in the equatorial western Pacific also have some influence on the WPSH east–west movement. The process of air-sea interaction is similar in the early and late summer, but the intensity of each meteorological factor is stronger in the early summer than that in late summer, which indicates that the air-sea interaction is more obvious in the early summer.

The anomalous characteristics of summer precipitation and atmospheric circulation in the East Asia–West Pacific Region (EA–WP) associated with the co-action of East Asia/Pacific teleconnection–Silk Road teleconnection (EAP–SR) are investigated in this study. The compositions of EAP–SR phase anomalies can be expressed as pattern I (+ +), pattern II (+ −), pattern III (− −), and pattern IV (− +) using EAP and SR indices. It is found that the spatial distribution of summer precipitation anomalies in EA–WP corresponding to pattern I (III) shows a tripole structure in the meridional direction and a zonal dipole structure in the subtropical region, while pattern II (IV) presents a tripole pattern in meridional direction with compressed and continuous anomalies in the zonal direction over the subtropical region. The similar meridional and zonal structures are also found in the geopotential height anomalies at 500-hPa, as well as wind anomalies and moisture convergence at 850-hPa. Finally, a schematic mechanism for the EAP–SR co-action upon the summer precipitation in EA–WP is built: (1) Pattern I (III) exhibits that the negative (positive) sea surface temperature (SST) anomalies over tropical East Pacific may cause the enhanced (weakened) convective activity dominating the West Pacific, trigger the positive (negative) EAP teleconnection and produce more (less) precipitation. Besides, the negative (positive) SST anomalies over the Indonesia Maritime Continent (IMC) may further weaken (strengthen) anomalous downward (upward) motion over the South China Sea (SCS), cause negative (positive) geopotential height anomalies at the middle troposphere and surrounding regions through the function of the tropical Hadley circulation. Then the negative (positive) geopotential height anomalies could motivate the positive (negative) EAP teleconnection through the northward propagation of wave-activity perturbation. Meanwhile, a positive (negative) geopotential height anomalous pattern over Eastern Europe motivates a Rossby wave train propagation from Western Europe to west-central Asia. This circumstance can cause suppressed (enhanced) convection and less (more) precipitation over northwestern India and Pakistan, which could strengthen the negative (positive) geopotential height and positive (negative) vorticity anomalies over central East Asia, resulting in a negative (positive) SR teleconnection along the Asian jet stream. A positive (negative) lobe over the Korean Peninsula and Japan corresponding to SR overlaps with a positive (negative) lobe of EAP, which strengthens the anomalous phase contrast on both sides of 120°E. Accordingly, summer precipitation anomalies in EA–WP exhibit the meridional tripole pattern and the zonal dipole pattern. (2) Pattern II (IV) indicates that the normal SST anomalies over the tropical East Pacific cause the weak tele-impact on the tropical West Pacific, while the positive (negative) SST anomalies over the IMC will lead to a negative (positive) lobe of EAP over the subtropical region. This circumstance can weaken the positive (negative) lobe of SR over subtropical region, causing compressed and continuous negative (positive) anomalies of 500-hPa geopotential height and positive (negative) surface precipitation anomalies from central East China to Japan.

The association of the biweekly intraseasonal (BWI) oscillation in the Sea Surface Temperature (SST) over the South China Sea (SCS) and the Western North Pacific Summer Monsoon is authenticated using version 4 the Tropical Rainfall Measuring Mission Microwave Imager data (SST and rain) and heat fluxes from Ocean Atmosphere Flux project data during 1998–2012. The results suggest that the SCS involves ocean–atmosphere coupling on biweekly timescales. The positive biweekly SST anomalies lead the rain anomalies over the SCS by 3 days, with a significant correlation coefficient ( r  = 0.6, at 99 % significance levels) between the SST-rain anomalies. It is evident from lead/lag correlation between biweekly SST and zonal wind shear that warm ocean surface induced by wind shear may contribute to a favorable condition of the convective activity over the SCS. The present study suggests that ocean–to-atmospheric processes induced by the BWI oscillation in the SCS SST results in enhanced sea level pressure and surface shortwave radiation flux during the summer monsoon. Besides, it is observed that the SCS BWI oscillation in the changes of SST causes a feedback in the atmosphere by modifying the atmospheric instability. This suggests that the active/break biweekly cycle of the SST over the SCS is related by sea level pressure, surface heat fluxes and atmospheric instability. The potential findings here indicate that the biweekly SST over the SCS play an important role in the eastward and the southward propagation of the biweekly anomalies in the Western North Pacific.

Hainan,an island province of China in the northern South China Sea,experienced two sustained rainstorms in October 2010,which were the most severe autumn rainstorms of the past 60 years.From August to October 2010,the most dominant signal of Hainan rainfall was the 10-20-day oscillation.This paper examines the roles of the 10-20-day oscillation in the convective activity and atmospheric circulation during the rainstorms of October 2010 over Hainan.During both rainstorms,Hainan was near the center of convective activity and under the influence of a lower-troposphere cyclonic circulation.The convective center was initiated in the west-central tropical Indian Ocean several days prior to the rainstorm in Hainan.The convective center first propagated eastward to the maritime continent,accompanied by the cyclonic circulation,and then moved northward to the northern South China Sea and South China,causing the rainstorms over Hainan.In addition,the westward propagation of convection from the tropical western Pacific to the southern South China Sea,as well as the propagation farther northward,intensified the convective activity over the northern South China Sea and South China during the first rainstorm.

Since the early or late onset of the South China Sea summer monsoon （SCSM） has a large impact on summer monsoon rainfall in East Asia, the mechanism and process of early or late onset of the SCSM are an worthy issue to study. In this paper, the results analyzed by using the observed data show that the onset date and process of the SCSM are closely associated with the thermal state of the tropical western Pacific in spring. When the tropical western Pacific is in a warming state in spring, the western Pacific subtropical high shifts eastward, and twin cyclones are early caused over the Bay of Bengal and Sumatra before the SCSM onset. In this case, the cyclonic circulation located over the Bay of Bengal can be early intensified and become into a strong trough. Thus, the westerly flow and convective activity can be intensified over Sumatra, the Indo-China Peninsula and the South China Sea （SCS） in mid-May. This leads to early onset of the SCSM. In contrast, when the tropical western Pacific is in a cooling state, the western Pacific subtropical high anomalously shifts westward, the twin cyclones located over the equatorial eastern Indian Ocean and Sumatra are weakened, and the twin anomaly anticyclones appear over these regions from late April to mid-May. Thus, the westerly flow and convective activity cannot be early intensified over the Indo-China Peninsula and the SCS. Only when the western Pacific subtropical high moves eastward, the weak trough located over the Bay of Bengal can be intensified and become into a strong trough, the strong southwesterly wind and convective activity can be intensified over the Indo-China Peninsula and the SCS in late May. Thus, this leads to late onset of the SCSM. Moreover, in this paper, the influencing mechanism of the thermal state of the tropical western Pacific on the SCSM onset is discussed further from the Walker circulation anomalies in the different thermal states of the tropical western Pacific.

The seasonality of the interaction between convection over the western Pacific and general circulation in the Northern Hemisphere (NH) is analyzed in the present paper with singular value decomposition (SVD) and empirical orthogonal function (EOF) analysis approaches, based on 500 hPa monthly mean geopotential height data and high-cloud amount data. The analyses demonstrate that coupled dominant patterns in the interaction between the convection over the western Pacific and the general circulation in NH are different in various seasons. In spring, the convection over the western Pacific is closely related with the western Atlantic (WA) and North Pacific (NP) like patterns of the general circulation in NH, and some associations between the WA and NP like patterns and the El Nino / Southern Oscillation (ENSO) cycle are also existed. The Pacific Japan (PJ) pattern is the dominant pattern in the interaction between the interannual variabilities of the convection over the western Pacific and the general circulation in NH summer. The WA like pattern and 3-4 year period oscillation are also relatively obvious for the summer case. In autumn, the convection over the western Pacific is closely linked with the Eurasian (EU) like pattern and the Atlantic oscillation in the general circulation in NH, it is suggested that in autumn the variation of convective activity over the western Pacific is largely affected by the general circulation anomaly (cold air from high latitudes) through EU like teleconnection pattern. Abrupt change happened by the end of 1980's in the autumn interaction. The strong interaction between the western Pacific (WP) and EU like patterns in the general circulation in NH and the convection over the western Pacific and a linear trend of increasing of this interaction are also suggested in winter. It is also demonstrated that the interaction in summer and winter is stronger than in the transition seasons (spring and autumn).[PUBLICATION ABSTRACT]