DETECTION OF MULTILAYER CIRRUS CLOUD SYSTEMS USING AVHRR DATA - VERIFICATION BASED ON FIRE-II IFO COMPOSITE MEASUREMENTS

A numerical scheme has been developed to identify multilayer cirrus cl oud systems using Advanced Very High Resolution Radiometer (AVHRR) dat a. It is based on the physical properties of the AVHRR channels 1-2 re flectance ratios, the brightness temperature differences between chann els 4 and 5, and the channel 4 brightness temperatures. In this scheme , clear pixels are first separated from cloudy pixels, which are then classified into three types: cirrus, cirrus/low cloud, and low clouds. The authors have applied this scheme to the satellite data collected over the FIRE II IFO [First ISCCP (International Satellite Cloud Clima tology Project) Regional Experiment II intensive field observation] ar ea during nine overpasses within seven observation dates. Determinatio n of the threshold values used in the detection scheme are based on st atistical analyses of these satellite data. The authors have validated the detection results against the cloudy conditions inferred from the collocated and coincident ground-based lidar and radar images, balloo nborne replicator data, and National Center for Atmospheric Research C LASS (Cross-chain Loran Atmospheric Sounding System) humidity sounding s on a case-by-case basis. In every case, the satellite detection resu lts are consistent with the cloudy conditions inferred from these inde pendent and complementary measurements. The present scheme is well sui ted for the detection of midlatitude, multilayer cirrus cloud systems and tropical anvils.