|覃皓,农孟松,翟丽萍,李佳颖,张惠景,蓝盈,黄晴,邱滋,黄明华. 2024. 广西沿海一次弱热带低压破纪录暴雨过程的诊断分析[J]. 气象学报, (0):-, doi:[doi]
|Diagnosis and analysis of a record-breaking rainstorm process caused by weak tropical depression in Guangxi coastal
|英文关键词:Record-breaking rainstorm,Tropical depression,Boundary layer jet,Kinetic energy,Aageostrophic wind
| Based on the atmospheric thermal and dynamic diagnostic equation, the cause of the record-breaking tropical depression rainstorm process in the coastal area of Guangxi and the possible mechanism of the maintenance of the depression in 7－9 June 2023 are analyzed by using multi-source observation data and ERA5 reanalysis data. The results showed that: (1) Under the background of the interaction between the mid-high latitude and low latitude weather systems, the tropical depression moves slowly and circles over Guangxi, which contributes to the occurrence of the heavy precipitation process. The atmospheric thermal and water vapor factors have significant anomalies during the process. The normalized anomalies of the vertical integral of vapor flux divergence, precipitable water and K index reach -5.5, 3.2 and 1.3, respectively. (2) The precipitation is strongest from night to early morning, and the quasi-stationary mesoscale cloud clusters and the convective system "echo training" caused continuous local accumulation of precipitation, resulting in record-breaking rainfall. (3) From the night of the 7th (8th) to the early morning of the 8th (9th), the warm shear line (boundary layer jet) on the southeast (eastern) side of the tropical depression and the land surface friction provided the dynamic conditions for the occurrence and development of heavy precipitation. The convergence of the boundary layer jet on the 9th was stronger than that of the shear line on the 8th, and the frontogenic forcing was stronger. The increase of pressure gradient force caused by the strengthening of tropical depression system and the meridional advection of potential height which corresponding the pressure gradient force doing work process promote the growth of local kinetic energy, which is the reason for the development of boundary layer jet. (4) The tropical depression circulation continuously sucked water vapor from the South China Sea, and the convergence and vertical transport of water vapor made the wet layer thicker, which is conducive to the increase of precipitation efficiency. Continuous warm and humid transport is conducive to the maintenance of unstable stratification, which makes the convective unstable structure at lower atmosphere run through the whole process. Among them, the favorable configuration of vertical wind shear and atmospheric baroclinicity make the stratification more instability on the 9th than that on the 8th, which combined with the dynamic conditions led to more intense precipitation on the 9th. (5) The maintenance of the tropical depression system is mainly supported by the convergence effect of the horizontal wind. The contribution of geostrophic wind component is relatively weak in the whole process, while the horizontal divergence term of the ageostrophic wind component leads the change of local vorticity, which is related to the convergence of the tropical depression center after the inertia rotation of the ageostrophic wind.