Enhancement of the summer North Atlantic Oscillation influence on Northern Hemisphere air temperature

This study investigates the relationship between the summer North Atlantic Oscillation (SNAO)and the simultaneous Northern Hemisphere (NH) land surface air temperature (SAT) by using the ClimateResearch Unit (CRU) data. The results show that the SNAO is related to NH land SAT, but this linkage hasvaried on decadal timescales over the last 52 years, with a strong connection appearing after the late1970s, but a weak connection before. The mechanism governing the relationship between the SNAO and NHland SAT is discussed based on the NCEP/NCAR reanalysis data. The results indicate that such a variablerelationship may result from changes of the SNAO mode around the late 1970s. The SNAO pattern was centeredmainly over the North Atlantic before the late 1970s, and thus had a weak influence on the NH land SAT.But after the late 1970s, the SNAO pattern shifted eastward and its southern center was enhanced inmagnitude and extent, which transported the SNAO signal to the North Atlantic surrounding continents andeven to central East Asia via an upper level wave train along the Asian jet.