A study of the turbulence structure and flux transfer at scs surface during the onset of southwest monsoon

Turbulent fluxes were measured on the Xisha air-sea flux research tower in May 14-June 22, 1998 and May 7-June 17, 2000.The observational period can be divided into some synoptic stages:prior to onset, onset period, monsoon break, cold air and southwesterly period.The observational results show that corresponding to the onset of SCS monsoon the air-sea fluxes indicate considerable changes.This paper presented the preliminary analysis results of fluctuation and gradient measurements of wind velocity, air temperature and moisture at the air-sea flux tower.The wind spectrum and some parameters including latent and sensible heat obtained from the eddy correlation or profile method are shown with various statistical quantities of scaling parameters such as intensities of turbulence and friction velocity u*.Intensities of turbulence are estimated to the values of u/u=0.096, v/u=0.066 and w/u=0.045 respectively at about 10 m high during the measured period in 1998.Momentum flux is about 0.1 N/m2.The drag coefficient CD of momentum transfer is approximated by the statistical relationship 103CD=0.003u102+0.020u10+0.836.Furthermore, the analyzed results of four synoptic stages are compared and the special characteristics of flux transfer during the different stages around onset of SCS monsoon are discussed.Finally, through comparison of the Xisha fluxes with those obtained from Indian Ocean and western Pacific Ocean, we can see their differences and a possible link between the moisture fluxes and rainfall in continent areas.