Estimation of vertical profiles of cirrus particle sizes and ice mass content from ground based radar/radiometer measurements

The magnitude and even sign of the cirrus cloud feedback in the climatic system depend significantly on the characteristic particle size and ice mass content (IMC) (Ebert and Curry 1992). Gaining information about cirrus cloud microphysics requires development of remote sensing techniques. In an earlier paper, Matrosov et al. (1992) proposed a method to estimate ice water path (i.e., vertically integrated IMC) and characteristic particle size averaged through the cloud from combined ground-based measurements of radar reflectivities and IR brightness temperatures of the downwelling thermal radiation in the transparency region of 10-12 μm. For some applications, the vertically averaged characteristic particle sizes and IWP could be the appropriate information to use. However, vertical profiles of cloud microphysical parameters can provide a better understanding of cloud structure and development. Here we describe a further development of the previous method by Matrosov et al. (1992) for retrieving vertical profiles of cirrus particle sizes and IMC rather than their vertically averaged values. In addition to measurements of radar reflectivites, the measurements of Doppler velocities are used in the new method. This provides us with two vertical profiles of measurements to infer two vertical profiles of unkowns, i.e., particle characteristic sizes and IMC. The Simultaneous measurements of the IR brightness temperatures are still needed to resolve an ambiguity in particle size - fall velocity relationships.