A Study on Future Changes in Precipitation Associated with the Baiu Front Using CMIP5 Simulations

Abstract:

The Baiu front is a stationary front, which frequently appears in East Asia in early summer. In this study, utilizing outputs of ten Coupled Model Intercomparison Project Phase 5 (CMIP5) models, we examine future changes of precipitation near Japan during June in relation to the subtropical jet, which has been pointed out as one of the environmental fields that are favorable for the Baiu front.

Many models show there is more rainfall over the Pacific to the south of Japan islands in future climate (2080-2099) than in the current climate (1985-2004). However, relatively large variability among models is found over Japan islands and the Japan Sea: Six models (defined as group A) show decreases or small changes in rainfall over Japan islands and the Japan Sea and the peak of rainfall to the south of Japan, while four models (group B) show increases in rainfall over Japan islands and the adjacent regions. This tendency of each group is found both in current and future climates, which contributes to the differences in the pattern of future changes of rainfall between the two groups. In group A, the axis of the subtropical jet tends to be more tilted to the south toward the mid to lower troposphere from the upper troposphere than in group B. That means that the mid-tropospheric jet for group A is located to the south of that for group B. Areas of large moisture convergence in the mid-troposphere for group A are also found to the south of those for group B. It is suggested that the mid-tropospheric jet may affect distributions of precipitation through moisture supply. We will also examine changes in precipitation of the Baiu front in relation to other environments such as processes in the lower troposphere.

[Acknowledgment]: This work is supported by the Environment Research and Technology Development Fund (2A-1201) of the Ministry of the Environment, Japan.