Cirrus Properties and Cloud Scale Dynamics from mm-Wavelength Doppler Radar Moments Retrieval: Tropical and Mid-latitude Cirrus Comparison

Abstract: An innovative radar-only algorithm is developed and applied to the about 1-year Millimeter Cloud Radar (MMCR) data collected by the Atmospheric Radiation Measurement program at both SGP and TWP sites. This algorithm uses the first three moments of the Doppler spectrum to estimate the cloud microphysical properties and the mean air motion. The resulting statistics of the cirrus microphysical properties and the cloud scale dynamics are analyzed at each site. The comparison between these two sites shows that the cirrus in the tropics are generally colder and higher with larger ice particles and more condensed mass, which corresponds to larger mass weighted fall velocities. Moreover, the tropical cirrus clouds tend to be more likely related to an ascending environment than mid-latitude cirrus clouds where the cloud-scale vertical motion PDF is Gaussian-shaped and centered on zero.

The possible seasonal variations of cirrus properties at the two sites are shown and compared. The preliminary results suggest that the seasonal variations of cirrus properties at SGP are more obvious than those observed at TWP. A strong temperature dependence of IWC is found. Comparing with available parameterizations of IWC of cirrus cloud in the numerical models, an improved IWC based on the radar retrieval dataset is proposed.