PNNL

Abstract

This study examines future projections of sea level pressure change in the North Pacific and its impact on winter precipitation changes in California. The multi-model analysis, based on the Coupled Model Inter-comparison Project phase 5 (CMIP5) models under the Representative Concentration Pathway 8.5 (RCP8.5) scenario, shows a robust sea-level pressure change in the late 21st century over the western North Pacific in which both the Aleutian Low and North Pacific Subtropical High (NPSH) shift poleward in concert with a widening of the Hadley Cell. This change is partly explained by a systematic increase of static stability in the subtropics. However, over the eastern North Pacific, the projected NPSH changes exhibit a substantial inter-model spread, resulting in uncertain projections of precipitation changes in California. This inter-model spread in the eastern North Pacific is associated with a Pacific Decadal Oscillation-like surface temperature change in the western North Pacific and the resulting meridional temperature gradient change. This study points to a major source of uncertainty for the response of winter precipitation to global warming over the West Coast of North America: atmosphere-ocean coupling in the North Pacific.