Mesoscale features of tropical cyclone formations associated with the trade wind surges in the Western North Pacific

Observations have shown that during the late season some tropical cyclone (TC) formations in the western North Pacific are associated with strong trade winds located 5-15 degree to the north of the system center. Although the trade wind surges might play an important role during the formation process of these TCs, several aspects have yet to be studied, such as the mesoscale features and their roles on TC formation. This study attempts to study the evolution of the mesoscale features as well as the roles that the large-scale and the mesoscale processes play during the formation stage of these TCs.

To study the evolution of the mesoscale features, such as the activity of the mesoscale convective system (MCS), we have analyzed the high spatial resolution satellite data, including QuikSCAT 10-m wind and TMI/TRMM rainfall data. A conceptual model is proposed to describe the evolution of the mesoscale convections of the incipient disturbance due to the synoptic-scale trade wind surges. In addition, the formation of Typhoon Bolaven (2005) which is likely triggered by the trade wind surges is simulated using WRF (model resolutions of 60 km, 20 km and 4 km). Results show that WRF model can simulate reasonably well the evolution of the mesoscale convections and the development of the pre-TC disturbance. The external low-level forcing (associated with the trade wind surges) causes the MCSs of the disturbance to coil and lengthen. The merging of the strong vorticity patches (associated with the MCSs) results in the concentration and increase of low-level vorticity as well as the development of the disturbance. The vorticity and energy budgets will be analyzed using the model outputs to reveal the important processes of responsible for the formation of Bolaven.