Interdecadal change of the boreal summer circumglobal teleconnection (1958-2010)

The tropical-extratropical teleconnection during boreal summer is characterized by a circumglobal teleconnection (CGT) pattern in the northern hemisphere (NH). Around the late 1970s, there was an abrupt change in the coupled atmosphere-ocean system over the NH and global tropics. This study found that the CGT has experienced a significant change since late 1970s. During the recent epoch (1979-2010), the major CGT centers weakened with pronounced changes over the North Atlantic and Europe. Partial correlation analysis of 200-hPa geopotential height and the NH summer monsoon heat sources indicates that the change of Indian summer monsoon (ISM) rainfall has a global impact on the CGT, whereas other NH summer monsoons (West African, western North Pacific, and North American) have only a regional modification to the CGT. The weakening of the CGT pattern in the recent epoch is a consequence of weakened coupling between ISM rainfall and midlatitude circulation, which results from the reduced interannual variability of ISM rainfall due to changes in El Nio-Southern Oscillation properties. The large change of the CGT over the North Atlantic and Europe is attributed to a southward shift of upper-level westerlies and enhanced coupling to West African monsoon rainfall.