CIRRUS CLOUD PROPERTIES DERIVED FROM HIGH-SPECTRAL-RESOLUTION INFRARED SPECTROMETRY DURING FIRE-II .2. AIRCRAFT HIS RESULTS

This paper presents analysis of cloud observations by the High-Resolut ion Interferometer Sounder made from the NASA ER-2 aircraft during FIR E II. Clear and cloudy sky radiance spectra are presented in terms of differences between observations and radiative transfer model simulati ons. Doubling/adding radiative transfer model simulations demonstrate that the magnitude of the brightness temperature differences (Delta BT ) is a function of the cloud particle size distribution and the cloud ice water path. For effective radii greater than approximately 30 mu m (size parameter of 18) there is little spectral variation in the brig htness temperature (BT). An analysis of brightness temperature differe nces indicates that cirrus clouds over the FIRE II central site posses sed a small-particle mode. The cases analyzed had similar appearances in a plot of Delta BT between 11 and 12 mu m (BT11 - BT12) versus the observed Delta BT between 8 and 11 mu m (BT8 - BT11), suggesting simil arity in the microphysical properties of nongray cirrus. Brightness te mperature differences between cirrus cloud over the central site and t he Gulf of Mexico are presented to illustrate differences in the cirru s microphysical properties at the two different locations. Cloud effec tive emissivities and effective radiative temperatures were derived fo r observations over the FIRE central site using complementary lidar an d radiosonde data. Small variations in these effective properties were seen on 5 December and 22 November. Although they had similar effecti ve temperatures, the emissivities were very different. Very few clouds were observed to have an emissivity near unity.