2014年赤道东太平洋ElNiño事件发展以及停滞过程的成因

Abstract

The El Nino event in 2014 starts with the substantial warm sea surface temperature anomaly (SSTA) in the equatorial eastern Pacific, following the westerly wind event (WWE) over equatorial western Pacific from February to March 2014. But it is suspended from June to August after the warm SSTA in equatorial eastern Pacific weakening in April when the WWE disappears. Results show that the 2014 El Nino event is triggered by the WWE, which is induced by the wet phase of MJO propagating eastward from the equatorial Indian Ocean in February. In early March the dry phase of MJO arrives at equatorial western Pacific to weaken the WWE. And the MJO is decayed evidently after mid March. Afterwards the anomalous easterly over equatorial western Pacific is determined by the zonal SSTA gradient in equatorial western-central Pacific. After the MJO disappearance, the anomalous surface easterly could warm the local SST via the wind-evaporation feedback to enhance the sea surface depression in situ . Thus the evident cold advection anomalies are formed in the mixed layer of equatorial central Pacific, where the continuous warming is prevented to increase the local sea surface pressure. As a result, a negative zonal gradient of sea surface pressure anomalies is enhanced over the equatorial western-central Pacific, developing the anomalous easterly over the equatorial western Pacific. Such positive feedback between the easterly anomalies over equatorial western Pacific and the zonal SSTA gradient in equatorial western–central Pacific maintains from June to August 2014, when the El Nino event is suspended with the absence of WWE.