Preliminary analyses on characteristics of sea surface temperatures in Kuroshio and its extension and relations to atmospheric circulations

Abstract

A sea surface temperature (SST) based index, denoted as KI, is designed to characterize the holistic feature of Kuroshio east of the Tokara-kaikyo and its extension on the purpose of predict its SST trend. The KI is calculated on the base of the Hadley Center's monthly SSTs during the period 1941-2009. The wavelet analysis showed that the KI displays inter-annual and inter-decadal oscillations, dominated by quasi-triennial, quasi 7-yr and 20-yr time scales. In addition, the KI is shown to be phase-locking to seasonal cycles. It is found that there are significant temporally-lag correlations between the KI and the Pacific decadal oscillation (PDO) index as well as between the KI and the ENSO index. A set of composition analyses using the NCEP/NCAR reanalyses indicate that when the KI shows a positive anomaly, the SST becomes abnormally warm in the equatorial eastern. Pacific, the Hadley circulation is intensified, and consequently the transportation of the westerly momentum is enhanced. The enhanced Hadley circulation and transportation of the westerly momentum give rise to the deepened Aleutian low pressure, then cool the Kuroshio extension and the north Pacific basin and cause the KE extend east. The above " ENSO-PDO-Kuroshio" process need some response time, that is to say, we can forecast the SST variation on the Kuroshio on the basis of the ENSO and PDO, which is very significant to predict the climate in China.