Analysis on the Mechanism of the Heavy Snow Process in the Northeast of Tarim Basin, Xinjiang, in 2018

Abstract

An analysis was made on the routine data of meteorological stations, high-resolution satellite cloud images and the NCEP/NCA R 1°×1° reanalysis data during one instance of heavy snow precipitation that took place in northern Bazhou, Xinjiang on October 18, 2018, followed by a diagnostic analysis of physical quantities, including the large-scale circulation anomalies, upper and lower-level circulation conditions and water vapor transport. The following are the results: (1) the heavy snow precipitation process in northern Bazhou, Xinjiang is a heavy precipitation process largely caused by a convergence of severely cold air carried from Siberia by an upper vortex, and a strong, warm and humid air current from southwest China. During this weather process, the upper layer was dry and cold, while the lower layer was warm and humid; an obvious wind shear and convergence center appeared at 700hPa, 850hPa in the lower layer over northern Bazhou; the heavy precipitation area was located in the front of the trough bottom at 500hPa, on the left side of the lower-level shear line. 2) The secondary circulation formed on the right side of the upper-level jet stream entrance area at 200hpa and 300hpa enlarged the ascending motion of the heavy snowfall area, while the low-level easterly jet stream played a critical role in transporting and accumulating water vapor at 850hpa. 3) The variations of temperature at 850hpa and on the ground layer were of certain indicative significance to the forecast of the precipitation phase state, and the temperature field at 850hpa well-indicated the change from rain to snow. When the air temperature fell to 0.5°C or so, and the ground temperature fell below 0°C given T700hpa<-10°C and T850hpa<-2°C, it could be used as a criterion for the judgment of rain changing to snow. 4) The vapor condition, lifting force condition and unstable stratification condition in the numerically-forecasted physical quantity field, all had a good guiding effect on the heavy precipitation process that took place in the Yanqi Reclamation Area.