Statistical Characteristics of Snowfall on the Tibetan Plateau Affected by TCs Over the Bay of Bengal: An Observational Analysis

Abstract

In this study, the characteristics of tropical cyclones (TCs) over the Bay of Bengal (BoB) that affect snowfall on the Tibetan Plateau (TP) and spatiotemporal distribution of snowfall related to BoB TCs are statistically analysed by using multi-sources data from 1981 to 2020, with partitioning TC-influenced snowfall by tracking cloud clusters. The results show that 141 TCs formed during the 40-year period of 1981–2020, of which about 35% (50 TCs) impacted snowfall at 83% of meteorological stations on the TP during their northward or westward movement, and the average distance between the TC centre and the snowfall stations is 1277 km. The proportion of snowfall-related TC frequency shows a significantly decreasing trend with a predominant cycle of 10a. The TC-influenced snowfall frequency (SF), precipitation amount (PA) on a snowfall day and snow depth (SD) during 1981–2020 all show a non-significant weak decreasing trend, while TC-influenced snowfall is significantly increased in the eastern and southern edges of Xizang, western Sichuan and the southern margin of Qinghai. PA and SD in December account for more than 75% and 55% of the monthly total, respectively. The spatial pattern of PA could be objectively categorised into west-type (24%) and southeast-type (76%). The moisture transported by the BoB TC and a southerly jet stream formed between the trough and the western Pacific subtropical high (WPSH), the convergence of cold air and warm–moist airstream over the TP and the change in position of the south Asian high in the upper troposphere are significant factors causing the different spatial distribution. The results can provide reference for TC-related snowfall, SD prediction and disaster assessment on the TP.