Observational Analysis of Long-Term Changes of the Summertime South Asia High and Its Impacts on Tropical Cyclones over the Western North Pacific

Assessment of the impacts of global warming is complicated by the internally generated multidecadal variability since longer-term externally forced trends are embedded in the background of the multidecadal variability. Using the reanalysis datasets during 1958-2015, this study investigates the changes of the summertime South Asia high (SAH) on the climate change and interdecadal scales. It is found that the two centers of the SAH are associated with different patterns of the linear trends over the period 1958-2015, with an anomalous cyclonic circulation over the Iranian Plateau and an anomalous anticyclonic circulation to the north of the Tibetan Plateau. While the anticyclonic circulation over the Iranian Plateau was weakening, there has been little intensity change over the Tibetan Plateau in the background of global warming. The spatial pattern of the SAH on the interdecadal scale is similar to that of the long-term trend. The long-term and interdecadal variations of the SAH over the Tibetan Plateau are associated with different warming patterns. The upper-tropospheric anomalous anticyclone in the long-term trend is an atmospheric response to the greater warming rate over the central Asia. On the interdecadal time scale, the anomalous anticyclone is associated with the mid-level warming over the Tibetan Plateau. The interdecadal variations of the SAH are statistically correlated with the Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation (AMO). It is interesting that the shift of the tropical cyclone (TC) genesis over the western North Pacific shows similar changes during last 60 years.