Insensitivity of the Summer South Asian High Intensity to a Warming Tibetan Plateau in Modern Reanalysis Datasets

Abstract

The South Asia high (SAH) is a prominent circulation system of the Asian summer monsoon, exerting profound influences on the weather and climate in China and surrounding regions. Its formation and maintenance is closely associated with strong summertime continental heating in the form of surface sensible heat flux and the latent heat release in connection with the Asian monsoon. In this study, the possible response of the South Asian high intensity to the thermal condition change in the Tibetan Plateau is examined with four modern reanalysis datasets, including the Modern-Era Retrospective Analysis for Research and Applications (MERRA), MERRA version 2 (MERRA-2), the European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-Interim), and the Japanese 55-year Reanalysis (JRA-55). Despite the surface air warming in the four modern reanalysis datasets, reduced surface wind speed in three of the reanalysis datasets, and decreased surface sensible heat flux in the MERRA-2 dataset, there is no statistically significant trend in the SAH intensity over the period 1979–2015. One of the possible reasons is that the response of the upper-level circulation to the thermal condition change of the Tibetan Plateau occurs mainly in the 200-hPa subtropical westerly jet stream, which is located far away from the center of the South Asian high. Thus the South Asian high intensity is not particularly sensitive to the thermal condition change of the Tibetan Plateau, while the center of the South Asian high intensity over the plateau exhibits a northward trend over the period.