Impact of Boundary-Layer Clouds--A Case Study of Cover Hours.

Abstract Cover hours are defined as the cloud-cover fraction times the number of hours those clouds are observed. Case study statistics of cover hours during 1990 for nonprecipitating low clouds at Madison, Wisconsin, indicate the potential for climatic impact by boundary-layer clouds. A total of 1476.6 cover hours by all low clouds are observed, of which the subset of scattered boundary-layer clouds contributes 33%. The subset of low clouds that are turbulently coupled to the ground contributes 1199.1 cover hours, which is 81% of the total observed and 13.7% of the total possible 8760 hours per year.