Precursor synoptic‐scale disturbances associated with tropical cyclogenesis in the South China Sea during 2000–2011

Abstract

Precursor synoptic disturbance characteristics associated with 35 tropical cyclone (TC) genesis events in the South China Sea (SCS) during 2000–2011 were examined. All genesis events occurred between May and December. Six types of precursor synoptic disturbances are identified, and their low-level composite patterns are constructed. They are synoptic-scale wave train (29%), TC energy dispersion (14%), Pacific easterly wave (9%), Borneo vortex (11%), TC southwesterly shear induced vortex (23%), and others (14%). In 13 (22) of 35 genesis cases, precursor perturbations originated within (outside of) the SCS. The satellite IR image data are used to analyse mesoscale convective activity prior to TC genesis. It is found that mesoscale convective systems were observed at 83% of the genesis cases, whereas 54% of the genesis cases experienced multiple mesoscale convective system development at a single time. Most of synoptic disturbances associated with the tropical cyclogenesis occurred in the region where atmospheric quasi-biweekly oscillation (QBW) and Madden-Julian oscillation (MJO) modes are in an active phase. The synoptic disturbances-associated TC genesis events in the SCS are strongly modulated by atmospheric low-frequency oscillations (especially the MJO). Meanwhile, favourable precursor sea surface temperature signals are observed, primarily on the 10- to 20-day and 20- to 90-day timescales.