Analysis and Comparison of Air-Sea Flux in the Northern South China Sea (SCS) During the Monsoon Onset in 2002
CHEN Yi-De~1, JIANG Guo-Rong~1, ZHANG Ren~1, YAN Jun-Yue~2, YAO Hua-Dong~2, and TANG Zhi-Yi~21 Meteorologica College, PLA University of Science and Technology, Nanjing 211101 2 National Climate Center, China Meteorological Administration, Beijing 100081
From 24 April to 22 June 2002, before and after the South China Sea (SCS) monsoon onset, the 3rd experiment of air-sea flux observation was carried out at Xisha Qundao(16~o50′N, 112~o20′E) which is located in the northern part of South China Sea.A series of high quality and high frequency (1 time/min) data were gained in the experiment.Based on the datasets and the NCEP data at the same time, firstly this paper suggests that the summer monsoon onset firstly in the northern part of the SCS on 14 May and it onset in the whole SCS on 16 May by diagnosing the 850 hPa wind field.Secondly the momentum flux, sensible heat flux, latent heat flux and some other correlated factors are calculated and analyzed by flux-profile method.Thirdly the air-sea fluxes between the western Pacific and the South China Sea are compared in the past years to find their common and different characteristics.The three main results are shown as follows: (1) In the experiment, the mean momentum flux was 0.0458 W·m~-2, the mean latent heat flux was 94.06 W·m~-2, and the mean sensible heat flux was 4.07 W·m~-2.The three fluxes were smaller than those in the western Pacific.(2) The air-sea fluxes in the northern part of the SCS and their correlated factors were remarkably different before and after the SCS monsoon onset, and they also varied greatly under different weather conditions.Every factor evolved stably besides the daily variation before the monsoon onset.But after the monsoon onset, the daily variation enhanced, the high frequency turbulence increased, and every flux varied greatly in a short time, especially in the raining phase, which reflected that the meso-scale and microscale strong turbulence occurred in the acute weather background after the monsoon onset.(3) The northern part of the SCS had the oceanic common characteristics as well as the western Pacific.Its sensible heat flux is far smaller than its latent heat flux.But the northern part of the SCS might play a less important role in the global air-sea interaction than the western Pacific.The air-sea fluxes in the northern part of the SCS changed little from May to June according to the average of the three experiments.Moreover, there was a stable ratio of the sensible heat flux to the latent heat flux.The latent heat flux was about twenty times as much as the sensible heat flux, in other words, the Bowen ratio was about 0.05.