Dynamics of Atmospheric Teleconnections during the Northern Summer

Abstract

The mechanisms of northern summertime teleconnections are investigated using a barotropic model. In a series of numerical experiments the atmospheric response over the eastern Pacific-North America to an idealized local divergence source corresponding to the northward displacement of the ITCZ in the eastern Pacific is studied. It is found that the response is much stronger in June than in May and is strongest when the forcing is located north of about 10 deg N. This can be explained in terms of the refractive properties of the climatological summertime subtropical jet stream over North America. In another series of experiments the global response as a function of the longitudinal location of the tropical forcing is examined. A wave train emanating from the subtropics of the western Pacific near the Philippines, arching across the Aleutians and the Gulf of Alaska, and terminating with a high anomaly over the continental United States appears over a wide longitudinal range of local forcing, suggesting the existence of a normal mode for the northern summertime climatological flow. The normal-mode concept is supported by further experiments using extratropical forcings as well as free-mode integrations.