湖南主汛期旱涝与大气环流及春季海温的关系

Relations between Drought and Flood in Dominant Flood Season in Hunan and Circulation Characteristic and Sea Surface Temperature in Spring

利用1960-2006年NCEP/NCAR逐月再分析资料、NOAA月平均海表温度资料和湖南月降水资料等,在计算分析湖南主汛期旱涝变化特征的基础上,对湖南主汛期旱涝大气环流及其与春季海温的关系进行了分析。结果表明,湖南主汛期洪涝指数增大趋势显著,1990年代以来处于洪涝多发期。洪涝指数具有20年、9年和3-4年的周期;干旱指数存在22年、10年和2-4年周期。湖南主汛期旱涝与西太平洋副热带高压、中高纬度环流、南亚高压、低层流场、水汽输送等持续异常有关。当西太平洋副热带高压面积偏大,强度偏强,脊线偏南,西伸脊点偏西,鄂霍次克海地区多阻塞活动,南亚高压主体位置较常年偏西,来自南海的水汽输送较常年强,低层湖南大部分地区处于辐合气流控制之下,湖南主汛期易洪涝;反之,当西太平洋副热带高压面积偏小,强度偏弱,脊线偏北,西伸脊点偏东,鄂霍次克海地区少阻塞活动,南亚高压主体位置较常年偏东,来自南海的水汽输送较常年弱,低层湖南大部分地区为辐散气流控制,湖南主汛期易干旱。春季印度洋、赤道中东太平洋和黑潮海温是湖南主汛期旱涝变化的重要短期气候预测信号,春季印度洋和赤道中东太平洋海温偏高（低）有利于湖南主汛期降水偏多（少）,黑潮海温偏低湖南主汛期易少雨干旱。

Using the NCEP/NCAR reanalysis monthly data,NOAA monthly sea surface temperature data and monthly rainfall station data,drought and flood from 1961 to 2006 in dominant flood seasons in Hunan are analyzed by using %Z% index,and the variation characteristics of multi-scale drought and flood activities are analyzed by the wavelet analysis method.Meanwhile,relationships between the atmospheric circulation in drought and flood of dominant flood season and sea surface temperature in spring are alse studied.The results show that flood index significantly increases in the past 47 years,flood occur more frequently since 1990s.It is also found that there are significant periods of 20,9,3-4 years in the flood index,and 22,10,2-4 years in the drought index.The drought and flood in dominant flood seasons of Hunan has close relations with Western Pacific High（WPSH）,mid-high latitude atmospheric circulation,south Asia high,low-level stream field,water vapor transport and so on.The flood might occur in Hunan when the area of WPSH become bigger and stronger and extending southward of ridge line,westward of extending west ridge point,blocking activity of Okhotsk sea region is more,main position of South Asia high is westward than normal year,and meanwhile the water vapor transfer from South China sea is also stronger,the most of regions of Hunan in low-level is under the control of convergence.By contrast,when the area of WPSH become smaller and weaker,northward of ridge line,eastward of extending west ridge point,blocking activity of Okhotsk sea region is less,main position of south Asia high is eastward than normal year,and meanwhile the water vapor transfer from South China sea is also weaker,the most of regions of Hunan in low-level is under the control of divergence, and it could bring drought.The sea surface temperature in Indian,mid-east equatorial Pacific ocean and the Black Current in spring may be a prophase signal to predict the drought and flood in dominant flood season in Hunan.The sea surface temperature in Indian and mid-east equatorial Pacific ocean is higher（lower）,the precipitation in dominant flood season in Hunan will be more（less）.In addition,the sea surface temperature of Black Current in spring is lower,the rainfall in dominant flood season in Hunan will be less.