Sensitivity to Cloud Characteristics in SAGE II Simulations of Solar Occultation Measurements

(presentation part of MS Defense at the University of Wyoming)

Model simulations of Stratospheric Aerosol and Gas Experiment (SAGE) II extinction events at the 1020 nm aerosol channel have been used to determine possible cirrus cloud signatures in SAGE II scan data collected during October 1989. This study was limited to the lowest 25 km of the atmosphere, with clouds only appearing below 18 km. All modeled clouds used physical properties consistent with cirrus clouds including extinction coefficients at or near the .008 km^-1 threshold between optically thick cirrus and thin sub-visible cirrus. Four case studies of comparisons between SAGE II and modeled transmission ratio data show overall profile error ranging from 4 to 13 %. These findings demonstrate that cirrus clouds could be responsible for much of the signal detected in the SAGE II 1020 nm wavelength channel within the troposphere. A study was also performed to determine the relative sensitivity of the model to perturbations in the physical properties of a modeled cloud. The results of this study demonstrate that the model is more sensitive to cloud location (latitude, longitude and altitude of the cloud center) than to variations of extinction, radius, or thickness of a cloud.