Abstract:

Based on the daily precipitation and maximum temperature of 96 meteorological stations in Hu’nan Province, the NCEP/NCAR reanalysis data and SST data from NOAA, the abnormal characteristics and possible causes of Western Pacific Subtropical High (WPSH) in summer of 2013 and its impact on high temperature were analyzed. The results showed that WPSH in summer of 2013 was abnormal strong, and the position was continuously westward than normal, which led to strong descending airflow controlling Hu’nan, and then caused continuous high temperature and severe drought. The main causes of the WPSH anomaly are as follows: (1) From winter of 2012 to summer of 2013, the sea surface temperature (SST) in the eastern equatorial Pacific was consistently in a cold state and in the Indian ocean to western equatorial Pacific was persistently in a warm state, which strengthened the ascending and descending motion of the Walker circulation and Hadley circulation, and finally resulted in the WPSH to westward and strengthen.(2) The eastward extensions of South Asian high (SHA) again and again were accompanied with the northwestward development of WPSH. Dynamical forcing of the negative vorticity advection at the upper layer caused the descending airflow, which led to WPSH maintaining and then caused high temperature. (3) The anomalous northward movements of westerly jet and stronger of zonal circulation in summer of 2013 were favourable to the maintenance of WPSH. The convergence enhanced at 200 hPa upper layers, and the convergence center moved to the north of 30°N, which caused descending motion of WPSH on 500 hPa to strengthen and northward.

Key words: extreme high temperature and drought, western pacific subtropical high (WPSH), sea surface temperature (SST), south Asian high (SAH)

摘要：

利用湖南96个测站的逐日降水、日最高气温和NCEP/NCAR再分析资料、海温资料，分析了2013年夏季西太平洋副热带高压异常活动特征、成因及其对湖南高温干旱的影响。结果表明，2013年夏季西太平洋副高异常偏西、偏强，使得湖南一直处在高压下沉气流控制下，形成持续高温干旱天气。造成副高变异的原因主要有：（1）2012年冬季至2013年春季，赤道东太平洋海表温度持续偏低，印度洋—赤道西太平洋海表温度持续偏高，使得Walker环流和Hadley环流的上升和下沉运动得到加强，西太平洋副高西伸、加强；（2）南亚高压一次次东伸，通过强烈高空负涡度平流的动力强迫，造成西太平洋副高区内的下沉运动，导致副高稳定维持，天气晴热高温；（3）西风急流较常年偏北，纬向环流偏强，导致副热带高压在偏北位置稳定维持，200 hPa高空辐合增强，辐合中心位于30°N以北，造成500 hPa副高下沉运动区位置偏北、偏强。

关键词: 高温干旱, 西太平洋副高, 海温, 南亚高压