Baiu Rainfall Variability and Associated Monsoon Teleconnections.

Abstract

Century-long observations enable us to uncover an interesting out-of-phase variability between the first principal component of Baiu rainfall over the Japanese archipelago and the monsoon rainfall over India during the early summer season (June and July). The signatures of this contemporaneous relationship are clearly evident from analysis of long-period multi-source climate datasets. One of the findings suggest that the circulation near the subtropical region of the west Pacific Ocean tends to vary in-phase with that over the Indian subcontinent, so that an intensified (weakened) west Pacific subtropical high is accompanied by an intensified (weakened) Baiu circulation over Japan and a weakened (intensified) monsoon circulation over India. Additionally, the Baiu-Indian Monsoon relationship is well supported by middle and upper tropospheric circulation anomalies extending from the mid-latitude region of West-Central Asia up to the Far East. A pattern consisting of an anomalous low over the Caspian and Aral Sea region, a high over Mongolia and an anomalous low over Korea and Japan, tends to be associated with increased Baiu rainfall over Japan and decreased monsoon rainfall over India. An opposite configuration of the mid-latitude circulation pattern tends to accompany below normal Baiu rains over Japan and above normal monsoon rains over India. It is suggested that the two patterns oriented along the (a) west Pacific southern oceanic route and the (b) mid-latitude continental route yield a consistent dynamical basis for inferring the Baiu-Indian Monsoon rainfall teleconnections. ©2001, Meteorological Society of Japan.