Radiative Heating Rate Profiles over the ARM North Slope of Alaska Site

The Arctic energy balance is very sensitive to clouds and their impact on the radiative fluxes. Relatively small changes in the macro- and microphysical properties of the clouds can have significant impacts on the radiative affect of the clouds on both the surface and atmosphere. Arctic clouds are particularly challenging to study due to the relatively high frequency of mixed-phase clouds, the low contrast between the clouds and the ice-covered surface (when viewed from space), and the presence of a significant low-level inversion for a large fraction of the year.

We have developed a comprehensive cloud product dataset that provides the macro- and microphysical properties of all clouds over the Atmospheric Radiation Measurement (ARM) program's North Slope of Alaska (NSA) site in Barrow, Alaska. This dataset was constructed by utilizing a conditional retrieval framework to derive the cloud existence, phase, condensed water content, and particle size for both the liquid and ice hydrometeors throughout the troposphere using a combination of active and passive ground-based observations. This cloud retrieval framework requires that the atmospheric state be known; the atmospheric state profiles are derived from a combination of local radiosonde data, microwave radiometer estimates of integrated water vapor, and European Center for Medium-range Weather Forecast (ECMWF) output.

Radiative heating rate profiles, as well as surface and top-of-the-atmosphere fluxes, have been computed for multiple years of data collected at the NSA site. These radiation calculations utilize the profiles of atmospheric state and cloud properties. The computed surface and top-of-the-atmosphere fluxes are compared against observations at the surface site and by satellite overpasses; the statistics demonstrate that the retrieved cloud properties are reasonable. The radiative heating rate profiles are then analyzed as a function of water content, phase, height, solar zenith angle, and season to provide insight into the radiative impact of these clouds on the atmosphere and surface.