The cause of the rapid weakening of Typhoon“Bebinca”was analyzed in this paper,by using the NCEP FNL(Final)Operational Global Analysis data on 1°×1°grids and the Tropical Cyclone(TC)Annual Report.The result shows that during the middle to late stage of its life cycle,the meteorological environments did not sustain“Bebinca”to maintain its intensity:the water vapor transport at low level decreased significantly;cold air intruded from north at low to middle level;both the divergence at high level and the convergence at low level reduced at the same time in the late stage.All these above factors restrained the development of“Bebinca”.In particular,the rapid reduction of sea surface temperature(SST)was the main factor that induced the rapid weakening of the Typhoon,which occurred about 6 hour ahead of its weakening.Compared to the 500-850 hPa vertical wind shear,which shows a relatively high correlation with the weakening,the impact of the 200-850 hPa vertical wind shear on the intensity change was not significant.Therefore,the Typhoons in the South China Sea would possibly weaken and disappear rapidly in fall and winter.So we have to pay more attention to the time effectiveness of the forecasting and correct the results in time.
In this paper,the observational data from Marine and Meteorological Observation Platform(MMOP)at Bohe,Maoming and buoys located in Shanwei and Maoming are used to study the characteristics of air-sea temperature and specific humidity difference and the relationship between wind and wave with the tropical cyclones over the South China Sea(SCS).The heat and momentum fluxes from eddy covariance measurement(EC)are compared with these fluxes calculated by the COARE 3.0 algorithm for Typhoon Koppu.The results show that at the developing and weakening stages of Koppu,both these differences between the sea surface and the near-surface atmosphere from the MMOP are negative,and data from the buoys also indicate that the differences are negative between the sea surface and near-surface atmosphere on the right rear portion of tropical cyclones(TCs)Molave and Chanthu.However,the differences are positive on the left front portion of Molave and Chanthu.These positive differences suggest that the heat flux is transferred from the ocean to the atmosphere,thus intensifying and maintaining the two TCs.The negative differences indicate that the ocean removes heat fluxes from the atmosphere,thus weakening the TCs.The wind-wave curves of TCs Molave and Chanthu show that significant wave height increases linearly with 2-min wind speed at 10-m height when the wind speed is less than 25 m/s,but when the wind speed is greater than 25 m/s,the significant wave height increases slightly with the wind speed.By comparing the observed sensible heat,latent heat,and friction velocity from EC with these variables from COARE 3.0 algorithm,a great bias between the observed and calculated sensible heat and latent heat fluxes is revealed,and the observed friction velocity is found to be almost the same as the calculated friction velocity.
