Structure of Subtropical Mesoscale Convective Vortex during SoWMEX/TiMREX

The joint U.S.-Taiwan field experiment SoWMEX (Southwest Monsoon Experiment)/ TiMREX (Terrain-influenced Monsoon Rainfall Experiment) 2008 was held during the period of May 15 to June 30, 2008. During the intensive observation period (IOP) #6, a weak quasi-stationary mei-yu front lay across middle Taiwan and Taiwan Strait. Mesoscale convective systems were active over the southern area ahead of the front. A distinct mesoscale convective vortex (MCV) related with the MCS was observed. The dropsonde data of 2 flight missions (around 0000UTC and 0600 UTC 5 Jun) and the soundings over land are used to examine the kinematic and thermodynamic structure of the MCV.

The vortex was concentrated below 6km with maximum tangential winds between the boundary layer and 700hPa. The vertical wind shear was relatively small, less then 5 ms^-1 between 925-500hPa, and the vortex was upright and demonstrated downshear left precipitation. Dry air advection and sinking in the mid-troposphere over the north and northwest portions of vortex were present. Positive virtual potential temperature anomalies in the center and rear of vortex were associated with convective core and rear dry air entrainment, respectively. A lower-tropospheric meso-low beneath the rearward dry air was exhibited over the northwest periphery of the vortex. The estimated maximum vorticity was about 4x10^-4 s^-1 and occurred at 800hPa at 0000UTC, and 2x10^-4 s^-1 at 925hPa 6hrs later.