The impact of liquid water and ice in Arctic clouds on cloud radiative forcing and the surface energy budget

The effects of clouds on the radiative balance and surface energy budget in the Arctic are not known well, especially when both cloud liquid and ice water are present. Increased understanding of Arctic cloud processes would improve the accuracy of climate models for this region. This study uses observations taken during the 2008 Arctic Summer Cloud Ocean Study (ASCOS) to identify the impact of summertime Arctic clouds on the surface energy budget. A radiative transfer model (the Rapid Radiative Transfer Model, RRTM) is used to calculate both long wave (LW) and short wave (SW) cloud forcing of the observed cloud liquid and ice. The RRTM results are verified with the surface radiation observations from the ASCOS ice camp. A series of sensitivity studies are used to examine the effect of ice content, liquid content, liquid drop radii, and ice crystal radii on the surface energy budget. We find that the RRTM resolved the expected cloud effects such as LW cloud top cooling and SW warming under the clouds. The results of the surface validation show great consistency between the observations and the model, except at times when the cloud radar analysis (which includes necessary inputs for the RRTM) is suspicious. As the sensitivity studies are completed, we find that upper level clouds play a significant role in decreasing the cloud forcing due to lower level clouds; liquid water content in the upper level cloud is an important contributor. With these sensitivity studies we study the interactions between the upper and lower layer clouds and the resultant impact on the surface energy budget.