Wednesday, 12 July 2006
Grand Terrace (Monona Terrace Community and Convention Center)
Satellite observations and general circulation model (GCM) studies show that ice clouds have an important impact on earth's climate by influencing the radiation balance and hydrological cycle]. However, the value of ice water content (IWC) and precipitation simulated using the state of the art numerical models vary significantly. Occasional aircraft in-situ observations provide very valuable information about the microphysical properties of clouds, but this data cannot validate climate models on a global scale. Radar technology is increasing being used for remotely retrieving cloud microphysical parameters. Since radar can be operated continuously, it can provide long term measurements of cloud properties. An experimental satellite, CloudSat, that is planned to be launched in 2006, will carry a 94 GHz radar. This radar should provide a global picture of cloud microphysical properties including IWC that can be used to constrain these models. However, radar measures the equivalent reflectivity factor (Z) of the cloud particles, but not their mass. The accuracy of the retrieved ice mass or ice precipitation rates based on radar reflectivity is highly dependent on the algorithms used. These algorithms are usually developed based on in-situ aircraft or ground measurements, or in combination with radar and in-situ measurements. In most cases, these retrieval algorithms normally include just one variable, . In this paper, we will discuss the development of two algorithms for retrieving ice water content (IWC) and ice precipitation rate (Fm) as a function of temperature and Z using ice particle spectra measured in stratiform ice clouds in midlatitude and Arctic regions. These parameterizations will be compared with a) direct measurements of IWC using a Nevzorov probe, b) precipitation retrieved using an X-band Doppler scanning radar and a Precipitation Occurrence Sensor System (POSS), c) the Canadian Global Environmental Multiscale (GEM) and High Resolution Model Application Project (HIMAP) models, and d) derived IWC and precipitation from measured ice spectra during four field projects.
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