北太平洋副热带高压年际变异与ENSO循环之间的选择性相互作用

Selective interaction between interannual variability of North Pacific Subtropical High and ENSO cycle

利用NCEP/NCAR大气再分析资料以及Hadley中心海表温度资料,针对北太平洋副热带高压(简称副高)的完整系统,通过分析超前于ENSO事件的海平面副高年际异常特征及其对ENSO事件的触发作用以及ENSO事件对500 hPa副高和海平面副高的滞后影响,结果表明了北太平洋副热带高压年际变异和ENSO循环之间存在选择性相互作用.即在大多数情况下,一方面,前期海平面副高减弱会导致热带西太平洋表面西风异常,通过海洋平流过程触发El Nino事件在夏季发生发展,在秋冬季成熟;而另一方面,El Nino事件在秋冬季发展成熟后,增强了赤道中太平洋的对流性热源,通过对异常热源的动力响应,同期和次年夏季500 hPa副高增强,又通过增强的Hadley环流作用,副热带地区下沉运动增强,从而使得次年夏季海平面副高增强,增强的海平面副高又有利于触发下一个La Nina事件.副高年际变异和ENSO循环之间相互作用的选择性主要取决于副高异常是否接近于赤道以及ENSO事件本身的持续性.这种相互作用有利于在热带太平洋海气系统产生准两年振荡.

With NCEP/NCAR atmospheric reanalysis data and Hadley Center sea surface temperature data, this study investigates possible interaction between the North Pacific Subtropical High （NPSH） and the ENSO cycle, with emphasis on the role of the surface subtropical high anomaly in triggering an ENSO event and the impact of the ENSO event on both the 500 hPa and the surface subtropieal highs on the interannual timescale. Results exhibit that the interaction between the NPSH and ENSO is selective. In most cases, the preceding weakened surface subtropical high causes anomalous surface westerly in the tropical western Pacific whichtends to trigger an E1 Nino event to develop in summer and mature in autumn and winter mainly through oceanic advection process. On the other hand, the convectional heating strengthens over the central tropical Pacific when the E1 Nino event matures in autumn and winter. The simultaneous and subsequent summertime 500 hPa subtropical high intensifies as a dynamical response to the anomalous heating associated with the E1 Nino event. The subsequent summertime surface subtropical high also intensifies due to the enhancement of Hadley cell. Resultantly, the enhanced surface subtropical high tends to trigger next La Nina event. Therefore, the interaction between the NPSH and ENSO is in favor of generating a quasi-biennial oscillation. However, such an interaction is selective, which depends on if the NPSH anomaly is close to the equator and on the life cycle of ENSO itself.