The Tibetan Plateau Westerly Jet Stream During July–August and Its Linkage With Precipitation in the Tibetan Plateau

Abstract

Using gridded and station-observed precipitation datasets from the China National Meteorological Information Center, GPCC precipitation data, and ERA5 reanalysis data from 1980 to 2021, this paper identifies a westerly jet to the north of the Tibetan Plateau (TP) during July–August, which differs from the typical East Asian westerly jet and is named the TP jet (TPJ). The relationship between the meridional location of the TPJ and precipitation in the TP and the associated mechanism are investigated. The results show that the TP precipitation is closely related to the meridional location of the TPJ. When the TPJ is located farther north, more-than-normal precipitation occurs in the central-western TP, and less-than-normal precipitation occurs in the southern part of eastern TP, thereby constituting an east–west antiphase mode. This mode is reversed when the TPJ is located farther south. The four-quadrant conceptual model of the jet stream can explain the link between the location of the TPJ and the mode of TP precipitation. When the TPJ is farther north, an anomalous meridional-vertical circulation cell appears at the entrance of the TPJ, with the central-western TP located at the upward branch of this cell. The upward motion is conducive to the convergence of water vapour and the increase in total cloud cover and produces more-than-normal precipitation in the central-western TP. Meanwhile, an anomalous meridional-vertical circulation cell appears at the exit of the TPJ, which is opposite to that at the TPJ entrance. The downward branch of this anomalous cell governs the southern part of eastern TP, causing water vapour divergence and suppressing total cloud cover and precipitation. The results suggest that the TPJ should be considered a special system when exploring the cause of TP summer precipitation.