Midlatitude westward propagating disturbances preceding intraseasonal oscillations of convection over the subtropical western North Pacific during summer

Abstract

We start with an analysis of the abruptly enhanced convection over the subtropical western North Pacific (WNP) around late July, the so called "convection jump," and indicate that intraseasonal oscillations (ISOs) play a dominant role in this feature. Then, we analyze the extratropical circulation anomalies in association with the convection ISOs over the subtropical WNP, which are more common than the convection jump and thus provide a greater sample size. It is found that prior to convection ISO peaks, a well-defined wave train of alternating cyclonic and anticyclonic perturbations appears and propagates westward in the upper troposphere over the midlatitude North Pacific, and bends southward to the subtropical WNP. The present results imply that midlatitude circulation anomalies in the North Pacific may affect intraseasonal variability of climate in the subtropical WNP and East Asia during summer. Copyright 2007 by the American Geophysical Union.