Stratocumulus Cloud Properties Derived from Simultaneous Satellite and Island-based Instrumentation during FIRE

Abstract

Cloud parameters derived from visible and infrared window data from the Geostationary Operational Environmental Satellite (GOES) are compared to corresponding properties determined from instrumentation on San Nicolas Island off the coast of California during the First ISCCP Regional Experiment (FIRE) marine stratocumulus intensive field observations period in July 1987. Mean cloud amounts derived by applying the hybrid bispectral threshold method to the GOES data were 5% less than the island ceilometer measurements. Examination of the satellite imagery revealed that the apparent bias can be explained by the persistence of the clouds over the northwest part of the island during periods of clearing around the island. Diurnal variations in the cloud cover were very significant; minimum cloudiness occurred during the late afternoon and maximum cloudiness early in the morning. The satellite retrievals track this variation quite well. Satellite-derived mean cloud-top height is 53 m lower than that observed from the surface. Relationships were established between the satellite-derived cloud optical depth and two surface-observed quantities: cloud liquid water path and cloud thickness. Simultaneous observations of liquid water path and satellite-derived cloud optical depth were used to infer effective cloud-droplet radius, resulting in good agreement with correlative data. The diurnal variations in cloud amount are accompanied by changes in cloud thickness, cloud-top height, cloud liquid water path, and effective droplet size. These observations provide the most complete picture, to date, of the diurnal cycle of marine stratocumulus clouds, confirming previous satellite-based inferences of the diurnal behavior of marine stratocumulus at larger scales. Because of the limited area of the observations, further comparisons should be performed over other regions containing climatologically significant marine stratocumulus clouds.