Precipitation variability related to atmospheric circulation patterns over the Tibetan Plateau

Artikel i vetenskaplig tidskrift, 2024

Precipitation is affected by intricate atmospheric dynamic and thermodynamic processes. Horizontal winds are frequently used to represent the dynamic component as winds play a critical role in transporting moisture. Previous studies on precipitation over the Tibetan Plateau (TP) focused on the influence of summer monsoons and westerlies in isolation. However, the collective seasonal dynamics and their combined effects on the precipitation distribution remain less explored. This study aims to determine the seasonal evolutions of the wind patterns and the associated regional precipitation patterns over the TP using a neural network approach and focuses on their interannual variability and long-term trends. A self-organizing map (SOM) was used to classify the wind patterns based on 500 hPa winds and related precipitation from the ERA5 reanalysis. The classified wind patterns show seasonal shifts between the Asian summer monsoon circulations and the westerlies along with the westerly jets migrating between the north and south of the TP from summer to winter. The locations of abundant precipitation during the winter and transition seasons are mainly associated with variations in the intensity and locations of the strong westerlies. There is a significant positive trend in the occurrences of the summer-type wind pattern, which has likely led to a wetter TP, and an earlier-ended winter and advanced spring wind patterns. The interannual variability of westerlies is highly related to the variability of precipitation in the western TP during its wet season (January–April). In the eastern TP, the interannual variability of the precipitation is linked to the wind patterns associated with the westerly jets to the south of the TP, while precipitation variability in the central TP is controlled by thermodynamic components. This study reveals the spatial precipitation distributions according to the different wind patterns and identifies the contributions from atmospheric components to the regional precipitation over the TP.