Sensitivity of radiation flux estimation to cloud ice particle models over the equatorial western Pacific Ocean region

Abstract:

Cloud shortwave (SW) and longwave (LW) radiative effects at the top of the atmosphere (TOA) approximately cancel each other over cloudy regions associated with tropical deep convection. Previous studies proposed theories on whether the cancellation of cloud SW and LW radiative effects is merely a coincidence or due to some negative feedback mechanisms that maintain the near-zero balance. However, general circulation models (GCMs) show disagreeing simulated net (SW + LW) cloud radiative effects over tropical deep convection regions. In addition to GCM cloud parameterization uncertainties, the uncertainties in radiation parameterizations—including the bulk optical properties of ice clouds—in GCMs also contribute to the large spread of simulated net CREs among GCMs. In this study, a combination of active and passive satellite cloud retrievals is used to study the sensitivity of radiation flux calculations to ice particle models over the equatorial western Pacific Ocean region. We adopt the SW and LW versions of the Rapid Radiative Transfer Model (RRTM) for radiation calculations using two recently developed ice particle models, the aggregate model and the more microphysics-based two-habit model (THM). The sensitivity of CREs to the two selected ice particle models is investigated in different ice cloud regimes in terms of retrievals of cloud optical thickness and cloud top temperature.