1.Key Laboratory of Cloud-Precipitation Physics and Severe Storms,Institute of Atmospheric Physics,Chinese Academy of Sciences;2.Shanghai Typhoon Institute,China Meteorological Administration
According to the change rate of the gale-force wind radius (R17) of tropical cyclones (TC) in the Western North Pacific (WNP), they were divided into size rapid expansion (RE) events and size rapid contraction (RC) events. This work studied the evolution characteristics of precipitation cloud systems in the outer core regions of TC in RE events and RC events as well as the physical mechanism responsible for the R17 change. The satellite data of Tropical Rainfall Measurement Missions (TRMM) and Global Precipitation Measurement (GPM), the International Best Track Archive for Climate Stewardship dataset (IBTrACS) and Multiplatform Tropical Cyclone Surface Winds Analysis (MTCSWA) from 2007 to 2016 were used. The results show that: (1) the precipitation intensity in the TC outer core region of RE events is significantly higher than that in the RC events, indicating that the precipitation intensity in the outer core region of TC plays an important role in the expansion of R17. The distribution of heavy precipitation in RE events is looser than that in RC events during before period, which can act as a precursory signal to distinguish two kinds of the events. (2) The common characteristics of precipitation in the outer core region of TC in the RE and RC events include the stratiform (convective) precipitation with low (high) precipitation intensity and large (small) precipitation area, and dominant diabatic heating in the middle and upper (middle and lower) atmosphere. The standardized rainfall rates of stratiform precipitation and convective precipitation are similar. However, the precipitation area, precipitation intensity and standardized precipitation rate in the outer core region of RE events are higher than those in RC events. (3) The outer core region of TC in RE events features high inertial stability and high diabatic heating, so that the wind field has high kinetic energy, which is favorable for size expansion of TC. In addition, the enhancement of kinetic energy is also conducive to develop low-level inflow, promoting the expansion of R17 and the development of convective cells.