Abstract
We used observational data and the results from a high-resolution numerical simulation model to analyze the occurrence and development of an extreme precipitation event in the Ili Valley, Xinjiang, China on 26 June 2015. We analyzed the horizontal wavelength, period, speed, ducting, energy propagation and feedback mechanism of inertial gravity waves. A low-level convergence line was formed in the valley by the northerly and westerly winds as a result of Central Asian vortices and the trumpet-shaped topography of the Ili Valley. There was sufficient water vapor in the valley for the precipitation event to develop. A mesoscale vortex formed and developed on the low-level convergence line and the rainfall was distributed either near the convergence line or the mesoscale vortex. The low-level convergence line and the uplift caused by the terrain triggered convection, and then the convection triggered waves at lower levels. The combination of ascending motion induced by the lower level waves and the mesoscale vortex led to the development of convection, causing the precipitation to intensify. When the convection moved eastward to Gongliu County, it was coupled with the ascending phase of upper level waves, causing both the convection and precipitation to intensify again. We applied spectral analysis methods to verify that the waves were inertial gravity waves. The upper level inertial gravity waves propagated westward at a mean speed of −12 m s−1 with periods of 73–179 min and horizontal wavelengths of 50–55 km. The lower level inertial gravity waves propagated eastward at a mean speed of 8 m s−1 with periods of 73–200 min and a horizontal wavelength of 85 km. The more (less) favorable waveguide conditions determined whether the gravity waves persisted for a long (short) time and propagated for a longer (shorter) distance. Based on the mesoscale Eliassen–Palm flux theory, the wave energy of inertial gravity waves had an important effect on the maintenance and development of convection and precipitation by affecting wind strength and wind divergence. Feedback was mainly through the meridional and vertical transport of zonal momentum and the meridional transport of heat.
Highlights
Xinjiang is located in an arid and semiarid region of northwestern China
The shape and extent of the center of the precipitation were consistent with the observations, reproducing the center of extreme precipitation simulated precipitation were consistent with the observations, reproducing the center of extreme with an east–west orientation in the center of the Ili Valley and an area of relatively heavy rain with a precipitation with an east–west orientation in theThe center of theof
The Eliassen–Palm flux divergence at mid-levels in the east of the precipitation event that occurred in the Ili Valley on 26 June 2015
Summary
Xinjiang is located in an arid and semiarid region of northwestern China. Previous studies in this region have focused on drought disasters and there has been little research on extreme precipitation events, rainstorms and floods often occur during the summer and can have serious impacts on both the economy and peoples’ lives [1,2,3]. Atmosphere 2020, 11, 752 different from the monsoon regions in eastern and southern China and show a strong locality and variability. Research on precipitation in the arid and semiarid regions of northwestern China is clearly lagging behind that in the monsoon regions of China [1]. Further work is required into the mechanisms of precipitation in this area, especially extreme precipitation events
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