Dominant Modes of Spring Precipitation Anomalies and Circulation Characteristics in Tarim Basin, Central Asia

In recent years, extreme precipitation has occurred frequently in Tarim Basin with fragile ecological environment, which has aroused widespread concern. Using the daily precipitation observations from 42 stations in Tarim Basin during the spring of 1980–2021 and the monthly circulation reanalysis data from the European Centre for Medium-Range Weather Forecasts Reanalysis v5 (ERA5) as well as the statistical analysis and physical diagnostic methods, this paper investigates the abnormal modes of spring precipitation in Tarim Basin and the evolution characteristics and differences of atmospheric circulation in the same period. The results show that the spring precipitation anomalies in the Tarim Basin can be divided into two independent precipitation modes: the first mode (EOF1) is a uniform precipitation pattern throughout the region, and the second mode (EOF2) is an east-west inverse pattern. Thus, there are distinct differences in the characteristics of atmospheric circulation responsible for the abnormal modes of spring precipitation in the basin. When the precipitation in the whole basin is consistently excessive, the 500 hPa geopotential height is affected by the negative phase of the North Atlantic Oscillation (NAO), and the 700 hPa wind field is under the control of abnormal southwesterly wind. The water vapor transport is mainly caused by the anomalous water vapor uplift along the terrain in the middle latitude west of the Atlantic Ocean and south of the Arabian Sea. The Tarim Basin water vapor is collected through its west and south borders and flows out through its east border, with the net water vapor budget and atmospheric precipitable water abnormally above normal. The situation is opposite when the precipitation in the whole basin is less than normal with one accord. When there is a west-to-east precipitation gradient, Rossby wave trains can be generated in the North Atlantic and split into two branches in Western Europe, and the two parts spread to Tarim Basin commonly. In the west of Tarim Basin, there is an upward motion while the eastern part has a predominance of downward motion, providing the dynamic conditions for the west-to-east precipitation gradient. Under the influence of anomalous water vapor transport from the southwest and water vapor convergence, favorable water vapor conditions can be given to precipitation. When there is a west-to-east precipitation gradient, the net water vapor in the basin also shows an abnormal west-to-east transport pattern. Moreover, the atmospheric precipitable water is featured with an inverse phase distribution when the atmospheric precipitation mode is west-east inversed during the spring precipitation in Tarim Basin.