高频瞬变涡动反馈强迫对东亚/太平洋事件演变过程的作用

本文通过位势倾向方程研究了高频瞬变涡动反馈强迫(TEFF)对东亚/太平洋型在低频时间尺度上(8天以上)的演变过程(EAP事件)的影响。一个重要的发现是,无论正位相还是负位相的EAP事件,在对流层中低层上,TEFF对其中、高纬度两个异常中心的演变均起着重要的作用。尤其是高纬度中心,在对流层中层,TEFF异常在盛期前可解释其增强部分的50%左右;盛期之后则起着减缓其减弱的作用。TEFF异常可分解为由高频涡动热量通量的辐合辐散引起的TEFF_heat异常和高频涡动涡度通量引起的TEFF_vor异常。两者在对流层上层相互抵消、下层相互叠加,导致TEFF异常在对流层上层(低层)的作用要弱(强)于对流层中层。就TEFF_heat和TEFF_vor的相对贡献而言,正位相的EAP事件中,TEFF_vor的贡献较大;但在负位相EAP事件中,TEFF_heat的贡献则增大至与TEFF_vor相当的程度。这种TEFF_heat作用在负事件中的增强可能是与贝加尔湖以东地区对流层低层上斜压性的加强有关。

Role of High-Frequency Transient Eddy Feedback Forcing in the Evolution of East Asia-Pacific Events

In this study, the dynamic features of East Asia-Pacific (EAP) events are investigated in terms of high-frequency transient eddy feedback forcing (TEFF) through the geopotential height tendency equation. One important finding is that the TEFF anomalies contribute greatly to the development and maintenance of the high-and mid-latitude centers of the EAP event during its evolution. In particular, in the mid-troposphere, the anomalous TEFF can account for approximately 50% of the amplification of the high-latitude center before the peak of EAP event, and then it counteracts the decay process to some extent. The feedback forcing anomalies could be decomposed into two components: one is associated with the divergence or convergence of the high-frequency transient eddy heat flux (TEFF_heat) and the other is associated with that of the vorticity flux (TEFF_vor). These two components usually reinforce each other in the lower troposphere but counteract each other in the upper troposphere. Thus, the total TEFF anomaly is less important in the upper troposphere than in the lower troposphere. It is evident that the TEFF_vor anomalies account for a predominant fraction of the total TEFF anomaly in positive EAP events; in contrast, in negative events, the contribution of the TEFF_heat anomalies increases to such an extent that they are at least comparable to the TEFF_vor anomalies. The increased importance of the TEFF_heat anomalies in the formation of negative EAP events might be related to the enhanced lower-tropospheric baroclinicity over the area east of Lake Baikal.