Solar cycle modulation of the relationship between the boreal spring Northern Atlantic Oscillation and the East and Southeast Asian summer climate

摘要

Previous studies have suggested that boreal spring Northern Atlantic Oscillations (NAOs) exert a pronounced influence on the following East Asian summer monsoon (EASM) variability. This study reveals that the relationship between the spring NAO and the following EASM varies with the 11-year solar cycle. The analysis of the time-lag relationship between the NAO in May and the following summer rainfall indicates that during the low solar activity (LS) summers, a more robust relationship is established, with below-normal rainfall anomalies in South China and the Sunda Islands in relation to a positive NAO. In addition, the May NAO-related atmospheric circulation anomalies during boreal summer over East and Southeast Asia may well explain the distinct rainfall difference. The possible mechanism for this solar modulation is attributed to the changes in structure of the spring NAO and associated tripole SST anomalies in the North Atlantic. Specifically, in the LS phase, the North Atlantic tripole SST anomalies associated with the May NAO can strongly develop and persist into the early summer. These SST anomalies tend to induce a remarkable subpolar wave train across the northern Eurasian continent and an enhanced East Asian jet in the summer. Our results indicate that, for the summer climate prediction over East and Southeast Asia, both the spring NAO and the 11-year solar cycle should be considered.