Changes of the connection between the summer North Atlantic Oscillation and the East Asian summer rainfall

In this study, the relationship between the summer North Atlantic Oscillation (SNAO) and the East Asian summer rainfall was statistically diagnosed based on the European Centre for Medium-Range Weather Forecasts (ECMWF) 40-year and interim reanalysis data (ERA-40 and ERA-Interim) as well as precipitation data from the Global Precipitation Climatology Centre (GPCC). The results show that the decadal change of the SNAO pattern around the late 1970s significantly enhanced its connection with summer rainfall over central and northern East Asia. Over the period before the late 1970s, the SNAO-related circulations were dominant over the North Atlantic region. Consequently, there was a weak connection between the SNAO and the East Asian summer rainfall. However, over the period after the late 1970s, the SNAO pattern experienced a decadal change, with the southern center shifting eastward. Such changes in the SNAO pattern can alter the stationary wave activity over the Eurasian Continent, producing an anomalous meridional dipole pattern over East Asia. This dipole pattern can then change the divergence circulation, vertical motion, water vapor, and total cloud cover, which would consequently provide beneficial conditions for more (less) summer rainfall over central (northern) East Asia in a positive (negative)-phase SNAO year.