西北太平洋海温增暖对热带气旋潜在破坏力的影响:高分辨模式个例分析

IMPACT OF WARMER OCEAN SURFACE TEMPERATURE ON THE TROPICAL CYCLONE DESTRUCTIVE POTENTIAL OVER WESTERN NORTH PACIFIC:ANALYSIS OF HIGH-RESOLUTION CASE SIMULATIONS

以三个西北太平洋热带气旋(TC)为例,利用WRF(Weather Research and Forecasting)模式进行了一系列海表温度(SST)敏感性数值试验,揭示了西北太平洋SST增暖对TC的强度、尺度及潜在破坏力的影响及其机理。结果表明,在距TC中心100 km以内区域的SST升高有利于TC强度增加,但会减小TC内核尺度;而在距TC中心100 km以外的SST升高并不会使TC强度明显增加甚至使TC强度减弱,但同时会增加TC内核尺度。伴随着低层向眼墙的入流,升高的外区SST会使TC区表层的大气温度和湿度升高,造成眼墙附近海气温差和湿度差及向内的气压梯度力减小,进而减少进入TC眼墙内的感热和潜热,不利于TC增强,但有利于眼墙向外移动,使TC内核尺度增加。内区SST升高与外区SST升高对TC强度及尺度变化的作用机理相反。因此,当TC移过冷或暖洋面时,TC的强度和尺度的变化不仅取决于局地洋面的冷或暖状况,还取决于TC内区和外区SST的差异。由于TC内区和外区SST对TC强度和内核尺度的不同作用,可能存在一个临界范围,当暖池范围在这个临界范围之内时TC潜在破坏力随暖池范围的扩大而增大,但当暖池范围超过这个临界范围时TC潜在破坏力便不会随着暖池范围的继续扩大而增大,甚至会有所减小。

To reveal the impact of increased sea surface temperature （SST） on TC destructive potential over the western North Pacific （WNP）, a series of SST sensitivity experiments with the Weather Research and Forecasting （WRF） model is conducted for three tropical cyclone （TC） cases in the WNP. The results show that, the SST increases over different radial extents play different roles in determining TC intensity, size, and potential destructiveness. The inner SST increase within approximately 100 km of TC center promotes TC intensification, but reduces TC inner-core size. In contrast, the outer SST beyond 100 km of the TC center contributes greatly to the growth of TC inner-core size, but reduces TC intensity. Further analysis indicates that, as the inflow air moves towards the eyewall, warmer outer SST can gradually increase the underlying surface air temperature and moisture, reduce the inward-directed pressure gradient near the eyewall, and thus decrease the air-sea temperature and moisture differences, which will lead to less sensible and latent heat fluxes entering the eyewaU and then decrease the TC intensity, but with an outward centrifugal displacement of eyewall and thus an increase in the TC inner-core size. The opposite happens as the inner SST increases. Therefore, when a TC moves across a warm/cold pool, the changes of TC intensity and size are determined by not only the conditions of local SST, but also the SST difference between the inner and outer TC regions. Due to the different effects of inner-SST and outer-SST on TC intensity and inner-core size, the TC potential destructiveness does not monotonically increase with the expansion of the ocean warm pool. There exists a critical range of the ocean warm pool. The TC potential destructiveness may not increase and may even decrease once the size of ocean warm pool exceeds the critical range.