冬季东太平洋峡谷风的季节内变化及相联系的海气特征

Sub-seasonal variation of gap winds over the eastern Pacific and its associated air-sea interaction

基于高分辨的卫星资料和再分析资料,本文采用合成分析、相关分析和带通滤波等方法研究了季节内时间尺度上东太平洋峡谷风的变化,并首先发现冬季东太平洋峡谷风存在4~16 d的季节内变化周期。进一步分析表明在该时间尺度上峡谷风异常与局地海温异常之间的关系存在由负相关到正相关的明显转变,在峡谷风强度达到最大之前及最大时,峡谷风异常与局地海温异常之间的关系主要表现为大气对海洋的强迫作用,北风分量的加强使中高纬度干冷空气进入峡谷风地区,海表面的净热通量损失使得海温降低。在峡谷风强度达到最大之后其与局地海温异常的关系则转变为海洋对大气的强迫作用,冷海温异常可一直持续到峡谷风强度达到最大后的第六天。冷海温异常的维持使得湍流混合受到抑制,导致其上的海表面风速减小。此外,峡谷风的季节内变化可能与东太平洋至北美上空的大气环流异常及其演变有关。在湾区峡谷风达到最大之前,北太平洋海平面气压正异常逐渐东移南下并在其最大时到达墨西哥湾上空,使得北美高压增强,湾区两侧气压差增大,对应湾区峡谷风达到最大。

Based on high-resolution satellite observations and NCEP-CFSR reanalysis results,this study investigates the sub-seasonal variation of the winter gap wind over the eastern Pacific and its associated air-sea interaction.It is observed that gap wind displays a significant sub-seasonal cycle during the period of 4-16 days.In the sub-seasonal cycle,the relationship between the gap wind anomaly and its underlying sea surface temperature( SST) anomaly undergoes a significant transition when the gap wind reaches its peak phase.Before the peak phase,their relationship is negative,indicating an atmospheric-to-oceanic forcing. During this period,the increasing northerly winds blowtoward the Gulfs with a dry and cold air flow,enhancing the surface net heat fluxes loss,in turn leading to the SST decreased.After the peak phase ends,the relationship between gap wind anomaly and its underlying SST anomaly turns positive,corresponding to an oceanic-to-atmospheric forcing,and particularly worth noting is that the negative SST anomalies can last for 6 days.The associated cold SST anomaly in turn suppresses the turbulent mixing,causing the sea surface wind speed to decrease.In addition,the atmospheric circulation anomalies over the eastern Pacific toward North America may exert an influence on the sub-seasonal variation of the gap wind.Positive sea level pressure anomalies over the North Pacific move southeastward as the gap wind increases,and reach Mexico Bay when the gap wind reaching its peak.The sea level pressure anomalies over Mexico Bay enhance the North American High,so as to enlarge the pressure differences between the east and west side of the Gulfs,thereby contributing to the gap wind peak.