Meteorological Conditions and Cloud Effects on Surface Radiation Balance Near Helheim Glacier and Jakobshavn IsbrÆ (Greenland) Using Ground-Based Observations

The surface radiation budget is an essential component of the total energy exchange between the atmosphere and the Earth's surface. Measurements of radiative fluxes near/on ice surfaces are sparse in the polar regions, including on the Greenland Ice Sheet (GrIS), and the effects of cloud on radiative fluxes are still poorly studied. In this work, we assess the impacts of cloud on radiative fluxes using two metrics: the longwave-equivalent cloudiness, derived from long-wave radiation measurements, and the cloud transmittance factor, obtained from short-wave radiation data. The metrics are applied to radiation data from two automatic weather stations located over the bare ground near the ice front of Helheim (HG, 66.3290 degrees N, 38.1460 degrees W) and Jakobshavn Isbr AE(JI, 69.2220 degrees N, 49.8150 degrees W) on the GrIS. Comparisons of meteorological parameters, surface radiation fluxes, and cloud metrics show significant differences between the two sites. The cloud transmittance factor is higher at HG than at JI, and the incoming short-wave radiation in the summer at HG is about 50.0 W m(-2) larger than at JI. Cloud metrics derived at the two sites reveal partly cloudy conditions were frequent (42 and 65% of the period at HG and JI) with a high dependency on the wind direction. The total cloud radiative effect (CREnet) generally increases during melt season at the two stations due to long-wave CRE enhancement by cloud fraction. CREnet decreases from May to June and increases afterward, due to the strengthened short-wave CRE. The annually averaged CREnet were 3.0 +/- 7.4 W m(-2) and 1.9 +/- 15.1 W m(-2) at JI and HG. CREnet estimated from AWS indicates that clouds cool the JI and HG during melt season at different rates.

Automated summary

This study assesses the impacts of cloud on radiative fluxes near the Greenland Ice Sheet, revealing significant differences in cloud metrics and radiation fluxes between two research sites. Cloud radiative effects increase during the melt season, with differences in cooling rates between the two stations.