中平流层环流转型日期气候及异常特征

The climate and anomalous characteristics of the transformation date of middle stratosphere circulation

利用NCEP/NCAR北半球1958—1997年40a中平流层(10～70 hPa)逐日位势高度场再分析资料,计算出其余弦球函数～YC20的系数A20。根据A20稳定由负转正的日期,确定了中平流层各层环流由气旋型转换为反气旋型的日期。结果表明:1)由冬入夏,20 hPa环流最先由气旋型转换为反气旋型,平均为4月24日;6月17日向下传播到70hPa,历时54d,此时整个中平流层进入盛夏。2)50、70hPa环流转型日期具有明显的年代际变化特征。分析表明,50、70hPa环流转型日期与低纬平流层纬向风准两年振荡存在显著正相关关系。

We calculated the coefficient（A02） of cosine Spherical harmonics by using the NCEP/NCAR middle stratosphere（10—70 hPa） reanalyzed daily height field data from 1958 to 1997.Then we derived the transformation date of middle stratosphere circulation from cyclone to anticyclone on the basis of the date when A02 converted steadily from negative to positive.The result shows that：1）The 20 hPa circulation first transformed from cyclone to anticyclone（averagely on April 24） and then the same occurred at 70 hPa 54 days later,thus the whole middle stratosphere was in summer;2）There is notable interdecadal variation in the transformation date at 50 hPa and 70 hPa.Our study shows that there exists remarkable correlation relationship between the transition date of circulations at 50 hPa and 70 hPa and the quasi-biennial oscillation（QBO） of the low-latitude stratosphere zonal wind.