ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Formation of Boundary Layer Convergence Lines in Hetao Area and Their Convection Triggering Effect
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Abstract:
Based on dense ball sound data, dense field surface observation, ERA5 and the Linhe New Generation Weather Radar data, detailed analysis is conducted on the boundary layer convergence lines (BLCL) formed by the surface differences between the Hetao irrigation area and the Kubuqi Desert in Hetao Area of the Yellow River in July and August 2022, and also on the role of BLCL in convection triggering. The results indicate that the BLCL in the Hetao Area was formed by the combined influence of surface differences, boundary layer atmospheric circulation and complex terrain, and mainly occurred in the Kubuqi Desert which lies in the southeast of the Hetao irrigation area, and the length of BLCL ranged from 100 to 200 km. The BLCL was a shallow system with vertical thickness of approximately 1000 to 1100 m. The daily variation of BLCL was significant, with a high incidence from 12:00 BT to 17:00 BT, accounting for 80%. The probability of BLCL formation in July and August was as high as 60%, and 39% of BLCL could trigger convection. The prediction indicators about the formation of BLCL are as follows.The temperature in Hangjinhou Banner in Hetao irrigation area is 2.5 ℃ lower than that in Habailaigeng in Kubuqi Desert, with dew point temperature higher than 6℃ and relative humidity higher than 20%. Continuous strong southerly winds blow in the Kubuqi Desert and Mu Us Sandy Land in Hetao Area, with maximum wind of 10 m above the surface being stronger than 4 m·s-1. The sea level pressure is low in the west and high in the east. A dense isobaric zone is in the curved section of Yellow River and the pressure gradient is 3-4 hPa·100 km-1. The formation of BLCL is of great significance to the convection triggering in this area, which is manifested in convection triggering, strengthening, and organization. Under different environmental conditions and weather system superposition configurations, the BLCL could trigger local convection, organized severe convection, torrential rain in Hetao Area. The generation and convective triggering of Hetao BLCL in this specific area are closely related to the distribution characteristics of rapid increase in precipitation from west to east in Hetao Area.
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