氣膠衝擊颱風之模擬 ─ 納莉颱風(2001)

Abstract

Many numerical studies have shown that cloud microphysical processes can have significant impact on the track, structure and precipitation of typhoon. However, few studies have investigated the effect of varying cloud condensation nuclei (CCN) concentration on typhoon’s evolution. It is therefore important to understand the role of aerosol during typhoon’s developing phase. To address this issue, Typhoon Nari (2001) is selected for investigation because of its slow translation speed and special track which stays close to the land and aerosol sources for an extended period of time. The WRF model incorporated with a semi-two-moment mixed-phase cloud microphysical scheme which can properly resolve aerosol-cloud microphysical interaction is used to study such effects. The simulations show that different CCN conditions lead to significant changes in the track, intensity and axisymmetric structure of Nari. Under more polluted aerosol situation, the main rainband becomes more convective and produces wider stratiform region as a result of weakened warm-rain processes and enhanced ice-phase processes. Furthermore, the squall-line-like structure of the rainband becomes more prominent, including a stronger upper-level latent heat release and below cloud evaporation which lead to enhanced rear inflow that brings in mid-level dry air. This leads to a stronger level-cold pool and the invigoration of convective inflow. The differential high-level heating and lower level cooling in the stratiform region of the rainband caused by aerosols may also alter the overall thermal structure and development of this typhoon.