Impact of the North Atlantic Oscillation on the Dipole Oscillation of summer precipitation over the central and eastern Tibetan Plateau

Abstract

ABSTRACTAn analysis of the spatiotemporal variability in summer precipitation during the period 1961–2010 is presented based on monthly precipitation datasets from 66 meteorological stations in the central and eastern Tibetan Plateau (TP). By applying empirical orthogonal function (EOF) analysis, a strong reversal is found in the variability of summer precipitation between the northeastern and the southeastern TP on the inter‐annual timescale; this reversal is defined as the Dipole Oscillation in summer precipitation over the TP.Our analysis shows that the North Atlantic Oscillation (NAO) greatly controls the Dipole Oscillation in TP summer precipitation by modifying the atmospheric circulation over and around the TP. With the increased stationary wave activity spreading eastward from the North Atlantic to the TP, a pronounced wave train pattern bridges the North Atlantic Ocean and the TP. During the positive phase of the NAO, warm moist air from the oceans around Asia is transported by the southeastern flank of the anticyclonic anomaly over East Asia to the northeastern TP. This northward‐moving warm moist air encounters cold air masses transported by the northwestern flank of the cyclonic anomaly over the northeastern TP. The confluence of the cold and warm air masses subsequently strengthens cumulus convective activities and ultimately results in excessive precipitation over the northeastern TP. Meanwhile, as a cyclonic anomaly sets up over northwestern India and Pakistan, water vapour condenses into precipitation over northwestern India and Pakistan, inhibiting Arabian Sea moisture inflows into the southeastern TP and northeastern India. As a result, a precipitation deficit occurs over the southeastern TP. The opposite scenario occurs during the negative phase of the NAO.