Millimeter wave radars operating at 35 and 94 GHz are being used for the remote sensing of ice clouds. Two-dimensional particle probe measurements in clouds show that a single type of ice crystals (e.g., column, plate, stellar crystal, etc.) is often observed in a mixture with ice crystal aggregates. This may pose a problem for estimating the ice water content (IWC) with radar. Aggregates are generally larger than individual crystals and can contribute significantly to the reflectivity factor. However, estimation of their bulk properties based on radar parameters, may not follow the same relationship as single crystals. This could lead to appreciable bias in the estimates of cirrus cloud properties such as ice water content (IWC) using the effective reflectivity factor Z. If the fraction of Z corresponding to aggregates and single ice crystals can be determined, then better estimates of IWC may be obtained by using the proper relationships.
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