Abstract:

By using monthly precipitation of 18 meteorological stations in Hainan, the NCEP/NCAR monthly reanalysis data and NOAA SST during 1966-2017, an index of long-cycle drought-flood abrupt alternation(LDFAI) in the post-flood period was defined, and based on the index, climatic characteristics of drought-flood abrupt alternation and corresponding atmosphere-ocean anomalous characteristics in Hainan Island were analyzed. The results were shown as follows: (1) The interannual variation of drought-flood abrupt alternation during the post-flood period in the past 52 years was great, and it presented a definite interdecadal characteristics with a significant period of 14 a. In spatial distribution, the frequency of alternation events was highest in Baoting, Danzhou and Baisha, and it was higher in the southeast coast and lowest in Ledong. The average intensity was stronger in northern part and central areas while it was weaker in the southwest areas. (2) In drought period in drought turning to flood years, the west Pacific subtropical high (WPSH) was abnormally eastward and weaker. Hainan was located at the central area of the anticyclonic field, and there were downward movement area and moisture divergence area over Hainan, which resulted in less rainfall and drought in Hainan Island. In flood period, the East Asian major trough got stronger, then the cold air and the easterly flow on the southern of WPSH converged in Hainan. With upward convergence motion in the lower level and moisture transport confluence in the whole layers, it resulted in vast precipitation in Hainan. It was the opposite situation in flood turning to drought years. (3) LDFAI in the post-flood period had significant negative correlation with the sea surface temperature of central tropical Pacific.

Key words: Hainan Island, the post-flood period, drought-flood abrupt alternation, atmosphere-ocean anomalies

摘要：

利用1966—2017年海南岛18个气象站逐月降水量、NCEP/NCAR逐月再分析资料及NOAA海表温度资料，定义了后汛期旱涝急转指数（LDFAI），据此分析了海南岛后汛期旱涝急转的气候特征及其海气异常特征。结果表明：（1）近52 a海南岛后汛期旱涝急转现象年际变化大，并呈现一定的年代际特征，存在14 a的强显著周期。空间上，保亭、儋州和白沙发生频率高，东南部沿海次之，乐东最少；北部部分地区和中部强度最强、西南部最弱。（2）旱转涝年，旱期西太平洋副热带高压（副高）异常偏东、强度偏弱，海南处于反气旋流场中心区，且其上空为下沉运动区和整层水汽辐散区；涝期东亚大槽偏强，冷空气和副高南侧偏东气流在海南附近交汇，伴随低层辐合上升运动和整层水汽输送汇合，海南降水形势有利。涝转旱年情况相反。（3）后汛期LDFAI与前期和同期热带中太平洋海温存在显著的负相关性。

关键词: 海南岛后汛期, 旱涝急转, 海气异常