Temporospatial Distribution and Trends of Thunderstorm, Hail, Gale, and Heavy Precipitation Events over the Tibetan Plateau and Associated Mechanisms

Temporospatial distribution and trends of thunderstorm, hail, gale, and heavy precipitation events over the Tibetan Plateau (TP) as well as the associated mechanisms with observational data from 1979 to 2016 are investigated, which have not been fully studied under a changing climate. The results indicate that thunderstorm, hail, and gale events over the whole TP show significant decreasing trends, while heavy precipitation events have an insignificant increasing trend. The southeast and central south subregions have obvious significant decreasing trends in thunderstorm, hail, and gale events, while the northeast subregion has a significant increasing trend in heavy precipitation events. It is found that the atmospheric circulation anomaly caused by the northwestern Atlantic sea surface temperature (SST) anomaly associated with the North Atlantic Oscillation (NAO) should be responsible for these changes. A strong wave train triggered by the northwestern Atlantic SST anomaly propagates from the northern Atlantic to East Asia through Europe, and induces a more upper-level warming over the TP and an anomalous anticyclonic circulation near the Lake Baikal, resulting in a more stable atmosphere and blocking effect, which forces the midlatitude westerlies and associated cold air to shift poleward. The weakened cold-air advection over the TP decreases the baroclinic instability and convection initiation, and finally causes the significant decreasing trends in severe weather events. On the other hand, the enhanced easterly winds in the southern flank of the anticyclonic circulation can significantly increase the water vapor flux from the eastern boundary of the TP and heavy precipitation events in the northeast subregion.