Monday, 10 February 2003: 5:15 PM
Teleconnection and US Rainfall Anomalies during the Northern Summer
The summer time teleconnection and its association with US summer rainfall was studied in this work. A significant teleconnection pattern was found before late 1970s, which links the East Asia-West Pacific (EAWP) summer monsoon and North America rainfall anomalies. It shows up a meridionally orientated structure over the East Asia-West Pacific section, and excites a wavetrain pattern in the midlatitude, which propagates eastward to North America. Through this teleconnection pattern, a weak EAWP summer monsoon can induce heavy rainfall over the northwest coast of North America and deficient rainfall near the Great Lakes. After late 1970s, the prominent impacts on US summer rainfall come from central and east Pacific. A wavetrain pattern links the convection anomalies over the central and eastern Pacific and a continental scale rainfall anomaly over US.
Numerical experiments with a barotropic model and an AGCM show that the teleconnection patterns are directly related to the fluctuation of the heat source in the tropical and subtropical regions. Different from in winter, the summertime teleconnection pattern is sensitive to the forcing distribution, and external forcing plays an more important role.
Numerical experiments also reveal role of air-sea interaction in the West Pacific-North America teleconnection pattern. Strong convective heating over the tropical western North Pacific can induce positive SSTA in the midlatitude North Pacific through increasing downward solar radiation, and SST anomalies can in turn further enhance the convection over the Philippine Sea and the anticyclone and cyclone dipole over the North American sector. This positive feedback between tropical WNP and extratropical North Pacific provides a self-maintaining mechanisms for the WPNA teleconnection.