Based on the ridge line of the western Pacific subtropical high (WPSH) and the theory of gradient wind approximation, a dynamic index for the westward ridge point (WRPI) of the WPSH is defined. Owing to its definition, the new dynamic index can be used to analyze the evolution of the WPSH at various time scales over most isobaric surfaces. The WRPI comprises two dimensions labeled ZWRPI and MWRPI, which depict the zonal and meridional movement, respectively, of the westward ridge point of the WPSH. The rationality and reliability of the dynamic index were validated using reanalysis atmospheric circulation, outgoing longwave radiation, surface air temperature, and rainfall data. The WRPI series revealed that the westward ridge point of the WPSH generally advances poleward while withdrawing eastward. Furthermore, there were close relationships between the WRPI, atmospheric circulation, outgoing longwave radiation, and precipitation over East Asia and the western Pacific in summer. The significant correlation coefficients indicated that the ZWRPI and the MWRPI can reflect the impact of the zonal and meridional movement of the WPSH on the climate over East Asia and the western Pacific. The ZWRPI has no significant linear trend at the interdecadal time scale, indicating that the WPSH did not significantly extend westward in summer. The slight decrease of the MWRPI suggests that the WPSH moves southward but with an insignificant trend. Compared with indices proposed in previous studies, the WRPI showed advantages in objectivity, reliability, predictability, practicability, and therefore extensive potential for application.

This paper describes the study of the relationship between the thermal configuration of the Bay of Bengal (BOB)–Tibetan Plateau (TP) region and the precipitation anomaly in Yunnan, a province in China, in May using ERA-Interim data and precipitation data for May from 125 meteorological stations across Yunnan for 1979–2014. Results from the analysis indicate that the interannual variability of May precipitation in Yunnan is significantly modulated by the BOB–TP thermal configuration. Model runs with a linear baroclinic model suggest physical consistency. The thermal conditions over the BOB mainly impact the May precipitation anomaly in Yunnan via changes in water vapor transport from the eastern BOB northeastward to southwestern Yunnan. The second factor influencing precipitation anomalies relates to the characteristics and variability of cold air transport from the TP to northeastern Yunnan. When the BOB (the TP) is occupied by positive (negative) diabatic heating, a thermal gradient with a warmer (colder) center over the BOB and a colder (warmer) center over the TP is established, and more-than-normal (less than normal) precipitation in Yunnan will occur in May. This relationship can persist from April to the following May to some extent; therefore, the BOB–TP thermal configuration in April could be used to forecast May precipitation in Yunnan.

In this paper, we study the relationship between the covariability of the Indian summer monsoon (ISM) and East Asian summer monsoon (EASM) and the rainy season precipitation anomaly in the Mekong River basin (MRB) using ERA-Interim reanalysis data and precipitation from the Climate Hazards Group Infrared Precipitation station for 1981–2016. The results indicate that the interannual variability of the rainy season precipitation in the MRB is significantly modulated by the ISM and EASM covariability. Herein, the ISM mainly influences the rainy season precipitation west of the MRB, and the EASM mainly influences the rainy season precipitation over the southeastern MRB. When the Bay of Bengal (BOB) and South China Sea (SCS) are dominated by positive anomalies of diabatic heating associated with a stronger ISM and EASM, the anomalous westerly winds in the BOB and significantly anomalous easterly winds in the SCS, which carry more warm-wet air, induce a stronger than normal convergence and upward motion in the MRB. This results in much heavier rainy season precipitation in the MRB. Model runs with a linear baroclinic model confirm the observational analysis results.

Western North America (WNA) experienced an unprecedented heatwave from late June to early July 2021, which lies far outside the historical range. Based on the model outputs from Coupled Model Intercomparison Project Phase 6, we find that the likelihood of a heatwave over WNA similar to the 2021 one increases with global warming. Such a heatwave is projected to occur more frequently with increased extreme temperature and shortened return period. It means that a rare event in the current climate will be a more common event in a warmer climate, especially under a high‐emission scenario like the Shared Socioeconomic Pathways 585 (SSP5‐8.5). Moreover, we show a large expansion of areas over WNA that will break the 2021 record in the future with an increasing level of emission scenario. Nevertheless, some heatwave records west of the Rocky Mountains are still difficult to break, highlighting the specific extremity of the 2021 WNA heatwave.