Preliminary Study on the structures of Line-Echo Wave Pattern over the Ocean in the Subtropics

A line-echo wave pattern (LEWP) embedded within a mesoscale convective system (MCS) moved and passed southern Taiwan area on 7 June 2003. Part of such system captured by the scanning coverage of Chiku and Kenting Doppler weather radar where constructed a portion of Doppler radar network in Taiwan. Dual-Doppler wind synthesis from both radars thus could deduce the circulation and flow pattern accompanying with the system. It is believed that the present study was the first bow-shaped pattern that has been documented in East Asia.

The apparent differences between LEWPs observed in East Asia and the United States are their environments. A LEWP usually initiate and develop over a plain area in the US, with a value of CAPE greater than 2000 J kg^-1 and moderate to strong low-level vertical wind shear. However, the LEWP investigated by this study was triggered and organized over the ocean in the subtropical area. The value of CAPE was lower (less than 1000 J kg^-1) and fair vertical wind shear (~7.5 m s^-1). Preliminary results illustrated that the northern segment of LEWP resembled a comma echo, which is a feature near the declining stage of a bow echo. The vertical vorticity field revealed that an intense positive area existed at the northern end, and a weaker negative area was positioned behind the southern end. The vertical vorticity pair was more comparable to bookend vortices.