Large-Scale Characteristics of the Atmospheric Boundary Layer in the Eastern Pacific Cold Tongue–ITCZ Region*

Abstract

Abstract Observations from the Eastern Pacific Investigation of Climate 2001 (EPIC2001) field campaign and a simple mixed-layer model are used to study the large-scale structure and dynamics of the atmospheric boundary layer (ABL) in the eastern Pacific. Vertical and latitudinal distributions of the meridional pressure gradient, winds, and other variables are examined and the momentum balance of the mixed layer is explored for a latitudinal range from 0° to 10°N along 95°W including the equatorial cold tongue, sea surface temperature (SST) front, and convective region at the latitude of the intertropical convergence zone (ITCZ). The surface meridional pressure gradient is partitioned into contributions from the ABL, largely controlled by the gradient in SST, and from the troposphere above the boundary layer, mainly controlled by elevated heating and atmospheric wave activity. The mean meridional gradient in surface pressure is dominated (90%) by the ABL contribution; however, its temporal variability prim...