A clear-sky radiation closure study using a one-dimensional radiative transfer model and collocated satellite-surface-reanalysis data sets

Abstract

Earth's climate is largely determined by the planet's energy budget, i.e., the balance of incoming and outgoing radiation at the surface and top of atmosphere (TOA). Studies have shown that computing clear-sky radiative fluxes are strongly dependent on atmospheric state variables, such as temperature and water vapor profiles, while the all-sky fluxes are greatly influenced by the presence of clouds. NASA-modeled vertical profiles of temperature and water vapor are used to derive the surface radiation budget from Clouds and Earth Radiant Energy System (CERES), which is regarded as one of the primary sources for evaluating climate change in climate models. In this study, we evaluate the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) reanalyzed clear-sky temperature and water vapor profiles with newly generated atmospheric profiles from Department of Energy Atmospheric Radiation Measurement (ARM)-merged soundings and Aura Microwave Limb Sounder retrievals at three ARM sites. The temperature profiles are well replicated in MERRA-2 at all three sites, whereas tropospheric water vapor is slightly dry below similar to 700 hPa. These profiles are then used to calculate clear-sky surface and TOA radiative fluxes from the Langley-modified Fu-Liou radiative transfer model (RTM). In order to achieve radiative closure at both the surface and TOA, the ARM-measured surface albedos and aerosol optical depths are adjusted to account for surface inhomogeneity. In general, most of the averaged RTM-calculated surface downward and TOA upward shortwave and longwave fluxes agree within similar to 5 W/m(2) of the observations, which is within the uncertainties of the ARM and CERES measurements. Yet still, further efforts are required to reduce the bias in calculated fluxes in coastal regions.