Simulated response of the marine atmospheric boundary layer in the western Pacific warm pool region to surface flux forcing

Abstract

The atmospheric boundary layer (ABL) response to surface fluxes and prescribed advective and radiative forcings is tested in a column ABL model. Observations are used to run an ABL model in a marine tropical convective regime. The influence of surface fluxes and prescribed advective and radiative forcings potential temperature and specific humidity throughout the ABL is examined. The manner by which the different ABL processes interact with each other is investigated in light of recently demonstrated sensitivity of the simulated general circulation to flux parameterizations. Simulated near-surface temperature and sensible heat fluxes are in close agreement with observations, with both the advection and the sensible heat flux contributing approximately equally to ABL warming. Simulated near-surface humidity and humidity profiles are dryer than observed. The model exhibits very vigorous nonlocal ABL mixing that self-regulates the flux response in its surface flux formulation by reducing humidity gradients and subsequent evaporation. The total time-averaged simulated heat flux for two surface flux parameterizations tested is within the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Experiment (TOGA-COARE) required accuracy. When decoupled from model response, the ABL model formulation overpredicts (underpredicts) latent heat fluxes modestly. ABL depth is dominated by nonlinear terms involving interaction between different surface fluxes and the ABL turbulent mixing and between these fluxes and advective and radiative forcing. Simulations in coarse vertical resolution typical of General Circulation Models (GCMs) result in significant ABL deepening and drying over observed values but also in better agreement between the time-averaged simulated and observed surface heat fluxes. Copyright 2001 by the American Geophysical Union.