Uncertainty in Future Projection of the North Pacific Subtropical High and Its Implication to California Winter Precipitation

Abstract:

This study examines future projection of sea level pressure change in the North Pacific and its impact on winter precipitation changes in western North America. 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 21^st century over the western Pacific. Both the Aleutian Low (AL) and North Pacific Subtropical High (NPSH) are predicted to expand poleward in consistent with a widening of the Hadley cell, and this change is largely explained by the systematic increase of static stability. However, over the eastern Pacific, NPSH trend exhibits a significant inter-model difference, resulting in uncertain projection of precipitation in western North America. This model spread is associated with the Pacific Decadal Oscillation (PDO)-like sea surface temperature (SST) change over the western North Pacific and the resulting meridional temperature gradient change. This result indicates that, to better understand precipitation change over western North America in future climate, uncertainty of atmosphere-ocean coupling in the western Pacific needs to be reduced.