Abstract
The Qaidam Basin (QB) locates over the northeast of the Tibetan Plateau (TP), where precipitation especially extreme precipitation possesses obvious local characteristics compared with that over the whole TP. This study tries to investigate cause of light (50% threshold) and extreme (95% threshold) precipitation in boreal summer in the QB, which is helpful to deepen understanding of the mechanism of precipitation formation in different regions of the TP. The extreme (light) precipitation thresholds in the eastern QB are greater than that in the western QB, with a value of 6~16mm (2mm) for most regions. There are two main moisture transport channels for light and extreme precipitation events. One is from the Eurasia and carried by the westerlies, which provides 48.2% and 55.8% of moisture for light and extreme precipitation events, respectively. The other moisture transport channel is from the Arabian Sea and the Bay of Bengal, which is transported toward the QB at the joint role of the South Asian summer monsoon and the plateau monsoon, contributing 51.8% and 44.2% of moisture for light and extreme precipitation events, respectively. The stronger moisture transport to precipitation mostly attributes to the enhanced moisture influxes from the western and southern boundaries. Additionally, the weaker moisture outflux across the eastern boundary is also responsible for the extreme precipitation. The circulation characteristics shows that, the precipitation in the QB has a closely relationship with the weak ridge over the Caspian Sea and Aral Sea, the enhanced South Asian summer monsoon and plateau monsoon, which are conducive to the moisture transport from the Eurasia and low-latitudes toward the QB. The meridional circulation enhances, meantime the westerly jet stream splits into east- and west-branch, and the south Asian high (SAH) strengthens, which are beneficial for the stronger convective motion. Especially, the trough in the northwest of the QB and the more significant east- and west-branch structure of westerly jet are the main circulation characteristics for the extreme precipitation events. Further analysis reveals that the apparent heat source over the QB is contributed to more synchronous moisture transport around the TP and its surrounding areas for light precipitation events, while the apparent heat source enhances 1 day prior to moisture transport from the east part region of the South Asian summer monsoon to around the eastern TP for extreme precipitation events. Meantime, the apparent heat source triggers an abnormal cyclone over the TP which can positively strength the local convective motion. Such abnormal configuration of atmospheric circulation and the influence of apparent heat source can explain the difference in cause of precipitation with different magnitude to a great extent in the QB.
Comparative Analysis of Internal Climate Variability and Model Uncertainty on Indian Summer Monsoon Extreme Precipitation