赤道地区纬向风系与ENSO事件的联系

EQUATORIAL ZONAL WIND SYSTEM AND ITS CONNECTION WITH ENSO

摘要:

利用Atuona MarquesasIs(9.48°S,139.2°W)站对流层最大西风层(150hPa)和最大东风层(850hPa)纬向风异常值的差值,构造了赤道中、东太平洋Walker环流强度指数I_d.并对Id、平流层下部QBO西风位相的长度和起始季节与ENSO事件的联系进行了研究。分析发现:I_d指数与南方涛动指数(SOI)具有显着的正相关关系;Walker环流圈在ElNiño(LaNina)事件期间减速(加速);ElNiño事件前20个月Walker环流圈开始加速、上层西风加速早且稳定;强ElNiño事件均出现在30hPaQBO西风位相持续期在5个季节以上,起始月在11～1月(北半球冬季)的过程结束之后。从而进一步提出西风动量自平流层中部向下传播,诱发赤道中、东太平洋Walker环流圈加速,导致海洋异变ENSO循环起始过程的”高层影响“构想

Abstract:

Constructed in the context of the difference in zonal wind anomaly (150 maximum westerly minus 850 hPa maximum easterly) over Atuona Marquesas Is. (9 48°S,139 2°W) is the equatorial central/eastern Pacific Walker circulation intensity index I_d, alongside the study of the relation of I_d and the length and starting season of lower-stratospheric QBO westerly phase to an ENSO event. It turns out that I_d is positively correlated, to high degree, with Southern Oscillation Index (SOI); the Walker circulation cell decelerates (accelerates) during the El Niño (La Nina) episode; the acceleration begins 20 months prior to the El Niño occurrence with upper westerly accelerated earlier and steadily; intense El Niño events happen when 30 hPa QBO westerly phase is maintained for more than 5 seasons and after the starting season (November to January, for northern winter) ends. Accordingly, we propose the “upper-level influence” concept stating that westerly momentum propagates downward from the mid stratosphere, inducing the acceleration of the Walker circulation cell over the central/eastern Pacific equatorially, thus leading to the beginning of the SSTA-related ENSO cycle.