Simulation of the Effects of SST Changes Induced by Tropical Cyclones on the Intensity of Tropical Cyclone Bilis (0604)

The effects of sea surface temperature (SST) changes induced by tropical cyclone (TC) Bilis (0604) and its preceding TC, TC Ewiniar (0603), on the intensity of TC Bilis were investigated by using numerical experiments. The observed SST changes induced by TCs Ewiniar (0603) and Bilis (0604) were first separated by using the smooth filtering and cylindrical filtering methods. The maximum SST cooling induced by TC Ewiniar (0603) exceeded 3℃, and that induced by the two TCs, Ewiniar (0603) and Bilis (0604), exceeded 6℃. The simulation results show that the SST cooling induced by TC Ewiniar (0603) and by two TCs reduced the intensity of TC Bilis (0604) by 6.2 m s^–1 and 7.6 m s^–1 within 60 h, respectively. Without the SST cooling induced by TC Ewiniar (0603), TC Bilis (0604) could have developed into a typhoon. The cold wake induced by TC Ewiniar (0603) was an important factor in inhibiting the intensity of TC Bilis (0604). Based on the analysis of the physical processes of the simulation results, a schematic diagram of the effects of SST changes induced by TCs on the intensity of TC Bilis (0604) was presented. The SST cooling reduced the upward heat flux and moisture flux at the surface of TC mainly within a radius of two latitudes, which in turn decreased the conditional instability and atmospheric moisture in the lower layer of TC, followed by weakening in TC precipitation, TC warm core, the upward vertical velocity of TC, and the inward radial wind in the lower layer of TC. The intensity of TC Bilis (0604) decreased accordingly.