Projection of the East Asian westerly jet under six global warming targets

Abstract

This study investigates the projected changes in the East Asian westerly jet (EAJ) under six global warming targets (1.5°C, 2.0°C, 2.5°C, 3.0°C, 3.5°C, and 4.0°C) relative to the present climate, using the outputs of CMIP5 models. The results show that the westerly tends to weaken slightly under the 1.5°C warming target. Under the 2.0°C target, it is projected to intensify south of the EAJ’s axis (approximately 40°N) and decay north of the axis. This change becomes increasingly evident under the 2.5°C and higher warming targets, which suggests that the EAJ’s axis will move farther and farther southward, but its intensity will change little with increasing global warming. Further analyses suggest that the change in the EAJ is closely related to the inhomogeneous rising rate of air temperature in the mid–upper troposphere. The relatively slow-rising air temperature in the mid–upper troposphere over the EAJ’s entrance and exit regions will lead to a negative (positive) meridional temperature gradient to the south (north), and will then accelerate (decelerate) the westerly on the EAJ’s south/north side.