Investigating Correlations of Horizontally Oriented Ice and Precipitation in North and South Pacific Maritime Clouds Using Collocated CloudSat, CALIOP, and MODIS Observations

Abstract:

In late 2007, the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the A-train changed its nadir-viewing angle. The original viewing angle of 0.3° (changed to 3° in 2007) allowed the polarization capabilities of the Lidar to determine the orientation of ice crystals. This is because viewing ice clouds at a nadir angle closer to 0° will yield specular reflection due to horizontally oriented ice. Similarly to how a vertical mirror will reflect a laser that is pointed vertically, oriented ice crystals return a strong integrated attenuated backscatter while also returning low depolarization values. This results in a distinguished depolarization and attenuated backscatter signature for horizontally oriented ice crystals as opposed to ice crystals that have no pattern in orientation (i.e. randomly oriented ice). In a preliminary search, it is found that up to 20% of warm (250 – 270 K) mid-latitude middle level clouds contain horizontally oriented ice. By taking advantage of the nearly synchronous orbits of the A-train constellation, an opportune dataset from 2006 and 2007 is compiled. This dataset includes collocated products from the CloudSat Cloud Profiling Radar (CPR), CALIOP, and the Aqua Moderate-resolution Imaging Spectroradiometer (MODIS). The Lidar capabilities of CALIOP in conjunction with the microwave sensitivity to precipitation provided by the CloudSat CPR give a unique point of view to explore the connection between these two physical phenomena. Similarly, the spatial imaging from MODIS yields insights into the phase of cloud layer tops and particles’ effective radii. MODIS aerosol optical depths may also shed light upon the cloud ice nucleation mechanisms that also may play a large role in the precipitation process. Preliminary results suggest that not all marine regions have the same occurrences of HOIC; the Northern Hemisphere demonstrates a strong seasonal dependence with a maximum in the winter months while the Southern Hemisphere is mostly seasonally independent. Using collocated CloudSat retrievals of precipitation we find a strong correlation between the occurrences of HOIC and precipitation which will be explored in the presentation.