Numerical Experiments on the Impact of Spring North Pacific SSTA on NPO and Unusually Cool Summers in Northeast China

摘要

A set of numerical experiments designed to analyze the oceanic forcing in spring show that the combined forcing of cold(warm) El Nino(La Nina) phases in the Nino4 region and sea surface temperature anomalies(SSTA) in the westerly drifts region would result in abnormally enhanced NorthEast Cold Vortex(NECV) activities in early summer. In spring, the central equatorial Pacific El Nino phase and westerly drift SSTA forcing would lead to the retreat of non-adiabatic waves,inducing elliptic low-frequency anomalies of tropical air flows. This would enhance the anomalous cyclone–anticyclone–cyclone–anticyclone low-frequency wave train that propagates from the tropics to the extratropics and further to the mid-high latitudes, constituting a major physical mechanism that contributes to the early summer circulation anomalies in the subtropics and in the North Pacific mid-high latitudes. The central equatorial Pacific La Nina forcing in the spring would, on the one hand, induce teleconnection anomalies of high pressure from the Sea of Okhotsk to the Sea of Japan in early summer, and on the other hand indirectly trigger a positive low-frequency East Asia–Pacific teleconnection(EAP) wave train in the lower troposphere.