An Analysis of the Eddy Kinetic Energy Budget of a Southwest Vortex during Heavy Rainfall over South China

Abstract

Based on the 6-hour-interval reanalysis data with 1°×1° resolution from the National Center for Environmental Prediction/the National Center for Atmospheric Research (NCEP/NCAR), the eddy kinetic energy (EKE) budget of a southwest vortex (SWV) that caused heavy rainfall in Guangxi over South China (from 1200 UTC 11 to 0000 UTC 13 June) is calculated. The results are as follows: (a) The SWV is a kind of subtropical vortex, with characteristics of both an extratropical vortex and a tropical vortex. (b) In the case examined, large-scale circulation and other perturbation fields contributed to the formation and development of the SWV. (c) When the SWV moved from weak large-scale circulation EKE areas to strong ones, the EKE of the SWV increased, and vice versa. (d) Sub-grid processes and frictional dissipation were the main sinks of the SWV EKE, which contributed to the decay of the SWV. (e) The residual term (RES) and the Total (composite effect of all right hand side (rhs) terms except the RES in the EKE equation) varied almost in the same tendency, which kept the EKE varying in a moderate way. (f) The EKE between 550 hPa and 850 hPa increased most intensively, corresponding to the vertical stretching of the SWV.

Key Words:

• SWV
• EKE
• barotropical transition
• baroclinic transition