| The global distribution of ice mass in cirrus clouds is very poorly known, but important for validating climate models that predict cirrus ice content. In this work theoretical modeling is carried out to investigate the feasibility of and possible techniques for high frequency microwave sensing of cirrus clouds from satellite. The discrete dipole approximation is used to compute the scattering properties for horizontally oriented ice crystals at frequencies of 85, 157, 220, and 340 GHz. Five particle shapes (solid columns, hollow columns, plates, planar rosettes, and spheres) and 18 gamma size distributions are considered. Upwelling brightness temperatures are computed with a polarized radiative transfer model. The brightness temperature depression ({dollar}Delta Tsb{lcub}b{rcub}{dollar}), relative to clear sky, is proportional to the ice water path (IWP), but the relationship depends strongly on the characteristic particle size and also on the crystal shape (typical range is a factor of two). Multiple frequencies and polarizations are shown to be useful for determining particle size and shape. Moderate IWP is detectable, e.g. 30 g/m{dollar}sp2{dollar} produces {dollar}Delta Tsb{lcub}b{rcub}{dollar} = 3{dollar}spcirc{dollar}K at 340 GHz for a typical distribution.; A multichannel passive microwave precipitation retrieval algorithm is also developed in this work. Bayes theorem is used to combine statistical information from numerical cloud models with forward radiative transfer modeling. A multivariate log-normal prior probability distribution contains the covariance information about hydrometeor distributions that resolves the nonuniqueness inherent in the inversion process. Hydrometeor profiles are retrieved by maximizing the posterior probability density for each vector of observations. Theoretical tests with brightness temperatures simulated from cloud model data show that a five layer structure with variable rain, graupel, and cloud water is as effective as more complex structures. The hydrometeor profile retrieval method is tested with four channel (10 to 85 GHz) aircraft-based microwave radiometer data from convection over ocean and land in Florida. Multiparameter radar data is used to verify the retrieved profiles. The results show that the method generally works, but that more research needs to be done to improve the use of cloud model information. |
