冬季海温异常影响北太平洋东部型风暴轴的数值试验

最强中心出现在160°W以东地区的北太平洋风暴轴定义为东部型风暴轴,针对这种短期气候异常现象,利用大气环流模式CAM 3.0对其可能的外部强迫机制进行探究,主要关注赤道中东部和黑潮海区正、负海温异常的影响。结果表明:赤道海区负海温异常对风暴轴东部型的出现有重要意义,当该海区海温为负(正)异常且黑潮海区海温正(负)异常时,风暴轴表现为东(西)部型。风暴轴在中、东太平洋地区低层斜压性的增强,是太平洋风暴轴中、东端天气尺度涡动活动增强的主要原因。当出现东部型时,北太平洋东部区域急流强度增强,涡动斜压增长偏强,涡动的热量和动量输送加强,风暴轴和急流的反馈也加强;反之亦然。冬季赤道海区引起的大气响应范围较广,而黑潮海区的影响较为局地,尤其是黑潮海区的负异常主要影响风暴轴入口区域,表现为关于海温异常强迫的符号非对称性。

A numerical simulation on effect of SSTA on North Pacific eastern-pattern storm track in winter

NCAR''s community atmospheric model v3.0(CAM3.0) is used to explore the possible external forcing mechanism of North Pacific eastern-pattern storm track(EPST) in winter,when the storm track often has its strongest center located east of 160°W.This paper mainly focuses on the effect of positive(P) and negative(N) sea surface temperature anomaly(SSTA) in the middle-east equatorial Pacific(EP) and the Kuroshio Current(KC).Results show that EP-N SSTA has significant meaning for the emergence of EPST.The EP-N(P) and KC-P(N) SSTA can lead to the eastern(western) pattern of the storm track.The activity of storm track in eastern North Pacific may be caused by the enhancement of low level baroclinicity.Specifically,when there is the eastern(western) pattern,the westerly jet in eastern North Pacific,as well as the eddy baroclinicity,the transportation of synoptic-scale heat and momentum,and the feedback between eddy waves and mean flow increase(decrease),and v.v..Compared with EP,the atmospheric responses to SSTA in KC are more local and asymmetric with respect to the sign of SSTA,and KC-N SSTA mainly influences the entrance area of the storm track.