A Case Study on the Convection Initiation Mechanisms of an Extreme Rainstorm over the Northern Slope of Kunlun Mountains, Xinjiang, Northwest China

Abstract

Extreme precipitation events have been occurring frequently worldwide, and their causative factors and convection initiation (CI) mechanisms have been attracting more and more attention in recent years. As a comprehensive study on the CI mechanisms of extreme rainstorms over the northern slope of the Kunlun Mountains (KLM), Xinjiang, based on both observational and high tempo-spatial numerical simulation, the major findings of this work are as follows: A cold pool (CP) was formed in the northwestern Tarim Basin under the influence of early precipitation evaporation, and it moved towards the northern slope of the KLM several hours before the CI. With the movement of the CP, a significant vertical temperature gradient was formed close to the leading edge of the CP, thereby enhancing local convective instability (up to ~10 PVU). In addition, the vertical shear of the horizontal winds at the leading edge of the CP led to a notable increase in the baroclinic component of moist potential vorticity, thus reinforcing the local conditional symmetric instability (up to ~8 PVU), providing another important unstable energy for the CI. In addition, the combined effect of the convergent lifting of a boundary layer jet (BLJ, the maximum wind speed below 1 km exceeding 10 m s−1) and the significant frontogenetical forcing (up to ~100 × 10−8 K m−1 s−1) at the leading edge of the CP were the causes of the release of the unstable energies. Further analysis of the frontogenetical forcing associated with the CP indicates that the convergence (up to ~2 × 10−3 s−1), diabatic heating and slantwise terms (indicates the baroclinicity and inhomogeneity of the vertical momentum in horizontal direction) were the major contributors, whereas the deformation term at the leading edge of the CP provided a relatively weaker contribution.

A Case Study on the Convection Initiation Mechanisms over the Northern Edge of Tarim Basin, Xinjiang, Northwest China

“…As can be seen from the corresponding simulation results (Figure 7b), the area of the simulated 6 h accumulated precipitation was biased by about 0.5 • to the south, which is consistent with the simulated composite reflectivity analyzed above. This kind of bias in the location of the accumulated precipitation often appeared in some similar studies [11][12][13][14], and it is probably due to some deficiencies of the reanalysis data providing the initial and boundary conditions for the simulation. The distribution of the precipitation rain band shows a similar orientation as the observed counterparts.…”

“…Severe convective weather is usually regarded as a serious and catastrophic weather phenomenon, which usually causes extreme weather events such as heavy rainfall, hail, destructive high winds, and sometimes tornadoes, leading to serious human casualties and economic losses [1][2][3][4][5]. In recent years, the frequency of such weather phenomena has further increased, with serious impacts on economic constructions, social development, and people's lives [6][7][8][9][10][11]. Despite significant improvements in weather forecasting techniques in recent decades, the accurate prediction and issuance of warnings for severe convective weather in a short period of time remain extremely difficult, and forecasting the convection initiation (CI) (i.e., the process whereby air parcels reach their level of free convection, then obtain and maintain positive buoyancy over a significant upward movement, and, finally, initiate a deep convective cloud), in particular, remains an important challenge in the field of weather forecasting [12][13][14][15][16][17][18].…”

Urbanization Effect on Changes in Extreme Climate Events in Urumqi, China, from 1976 to 2018

“…Urumqi, the provincial capital of Xinjiang, is the largest and the most-developed city in Xinjiang. It is located in the arid region of northwestern China, whose weather and climate are very sensitive to climate change [12,[37][38][39][40]. Therefore, it is important to study the UE on the local extreme climate events in Urumqi.…”