Northern Hemisphere Subtropical Highs

Dynamical Origin and Regional Impact of Decadal-Scale Fluctuations in the North Atlantic Subtropical High

This NSF-funded project aims to identify forcing processes (mostly in the form of large-scale diabatic heating in the tropics and subtropics) that drive the observed long-term trend in the characteristics of the North Atlantic Subtropical High (NASH), The intensification, westward expansion and strengthened western ridge movement of the NASH in the recent three decades have contributed to the increased interannual variance in the southeast (SE) U.S. summer rainfall (Li et al. 2011). These trends are projected by climate models to continue with increasing greenhouse gas (GHG) concentration in the atmosphere. We are employing idealized GCM simulations to quantify the contributions of past changes in monsoonal and tropical convective heating to the observed NASH trends. In addition, we are investigating the formation of summer subtropical highs from a Lagrangian perspective by tracking the large-scale mass transport throughout the year. 




Mass tendency within individual isentropic layers calculated from isentropic pressure (a) and derived from large-scale mass transport (b). (c) and (d) are the same as (a) and (b) except for total mass tendency (divergence/convergence) above individual isentropic levels.