热带气旋Haiyan(2013)快速增强过程内核涡度变化机制的数值模拟研究

选取西北太平洋热带气旋Haiyan(2013)为研究对象,利用中尺度数值模式WRF对其快速增强(RI)过程进行了高时空分辨率的数值模拟,推导出一个包含不同尺度系统相互作用的垂直涡度诊断方程来探究TC内核区域相对涡度的变化特征及其与RI的联系。诊断结果表明:涡旋尺度散度项(stre2)、倾斜项(tilt2)和垂直平流项(advv2)对涡度收支的影响最为重要。RI开始前,stre2在边界层内对涡度收支为正贡献,边界层之上则为负贡献;tilt2在低层促进涡度增加;advv2分布与stre2相反,在低层为负值,高层为正值。RI开始后,stre2在低层(高层)对涡度的正(负)贡献显著增强;tilt2在低层(高层)对涡度的促进(抑制)作用明显增强,但在中层出现正负贡献相互交替的情况;advv2在低层对涡度的正贡献也有所增强。

Numerical simulation on change mechanism of the inner-core vorticity in the rapid intensification of tropical cyclone Haiyan(2013)

Mesoscale numerical model WRF (Weather Research and Forecasting) was used to numerically simulate the Rapid Intensification (RI) process of Tropical Cyclone (TC) Haiyan (2013) over Northwest Pacific at high space-time resolution. A vertical vorticity diagnostic equation involving the interaction among systems with different scales was deduced to investigate the variation mechanism of inner-core vorticity of TC and its relation with RI process. Results show that vortex-scale stretching term (stre2), tilting term (tilt2) and vertical-advection term (advv2) play the most important role in vorticity tendency. Before the onset of RI process,the stre2 contributes to the generation of vorticity in the boundary layer, but it tends to suppress above the layer;the tilt2 promotes the vorticity tendency in lower atmosphere layers; the distribution of the advv2 is approximately contrary to that of the stre2. After the onset of RI process,the positive (negative) contribution of stre2 to vorticity tendency tends to strengthen at low (upper) levels;the tilt2 has more robust low-level upgrading influence as well as stronger upper-level reducing influence in company with the alternately positive effect and negative effect at mid-levels;the positive contribution of the advv2 is able to enhance at low levels.