Future Changes in Seasonality of the North Pacific and North Atlantic Subtropical Highs

Abstract

The subtropical highs have a zonal mean and a zonally asymmetric component related to the Hadley cell and land-sea contrast, respectively. Based on 37 Coupled Model Intercomparison Project phase 5 models, relative roles of the Hadley cell and land-sea contrast in future changes of the North Pacific and North Atlantic subtropical highs (NPSH and NASH) are evaluated. Both the NPSH and NASH are significantly enhanced during boreal spring (April–June) but not in summer (July–September). Although the zonally asymmetric component contributes to more than half of the enhancement during spring, the zonal mean component is responsible for the interseasonal contrast of the responses of the NPSH and NASH between spring and summer. The seasonally dependent Hadley cell changes are due to changes in tropical precipitation related to sea surface temperature (SST) warming, while enhanced land-sea contrast has comparable effects on the NPSH and NASH during both spring and summer, with important implications to U.S. regional precipitation.