The possible influence of Arctic Oscillation on South China Sea climate during boreal spring

Abstract

In this study, the possible influences of the springtime Arctic Oscillation (AO) on climate over South China Sea (SCS) has been studied, by employing monthly precipitation data (GPCP) and atmospheric circulation reanalysis data from NCEP-NCAR during the period of 1979-2013. Prior to analysis, the El Nino-Southern Oscillation (ENSO) signals have been linearly fitted and subtracted from the time series under consideration. To capture the major feature of the regional climate variability, multi-variable empirical orthogonal function (MV-EOF) analysis was performed, by taking into account sea surface temperature (SST), precipitation, and horizontal and vertical winds at 850 hPa over the domain of 3.75°S-23.75°N and 106.25°E-123.75°E. The first mode explains 27.8% of the total variance. The corresponding temporal variations of the first mode co-changes tightly with the spring AO. Their correlation coefficient is -0.4, being significant at the 0.05 level. Their out-of-phase relationship is even more dominant on the interannual time scales. During positive (negative) AO years, a cyclonic (anticyclonic) anomalous circulation is observed over the tropical Western Pacific in the mid- and lower troposphere. There are more (less) precipitation in the central SCS, corresponding to the circulation anomalies. There are two possible mechanisms linking AO and SCS climate. The first mechanism is the wave train along the westerly jet stream extending from northern Africa through mid-Asia to northern India. Along this route, there are two anomalous circulation centers in the upstream direction, one being located in the Bay of Bengal, and the other located in the Arabian Sea. The second mechanism seems to be related to the dipole-structure circulation anomalies over the North Pacific, which characterized by a dipole of anticyclone and cyclone located to the north and south of the northern Pacific storm tracks, respectively. Their phase and corresponding circulation center locations are crucial with regard to the AO-SCS links. In cases of a strong positive phase of southern Asian waves and negative phase of northern Pacific dipole, there is an enhanced anticyclone circulation over the SCS and reduced precipitation. In addition to the influences on the SCS climate from the atmosphere, positive feedback from the tropical western Pacific Ocean strengthens the anomalous north winds of SCS. Local SST of SCS mainly responds to (rather than affects) the atmospheric circulation.