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Ken Sassen's ruby lidars at the DOE-CART site (CF), and at the University of Utah facility for remote sensing (FARS) in Salt Lake City remotely sensed the detailed structure of hurricane Nora remnants as the cirrus passed directly overhead. Pulses of laser light are reflected from cloud particles back to a receiving telescope for processing. The cloud parcel height can be determined from the time it takes for a pulse to return. A measure of the cloud thickness (number, size, mass, and area of ice crystals per volume) at a particular location can be determined from the laser power returned from a cloud portion. A measure of the ice crystal geometry can be determined from the depolarization of the laser light reflected from cloud parcels. The lidar images show the cloud boundaries and structure as the upper level winds push the cirrus along. The depolarization ratio images show little depolarization during most of the time intervals studied, indicating that the ice crystals were likely oriented pristine hexagonal plates and/or columns. This interpretation is consistent with the in situ observations made on the Citation aircraft over the CART site. One of the most interesting observations is that the depolarization ratios show that the microphysical character of Nora's remnants was maintained as the cirrus crossed the country. This interpretation is consistent with observations of strong optical displays of halos and sundogs by this cirrus both in Salt Lake City and at the CART site. The cloud radar data is displayed for a longer time than the lidar data, though at the same place, the CART site. Be sure to note, by looking at the three frame slide show (movie) that the radar penetrates the thickest portions of cirrus, whereas the lidar beam is attenuated. The lidar depolarization ratio images (see the link to detailed images) are a measure of ice crystal geometry and orientation. Ice crystals with low depolarization ratio might be faceted crystals that are oriented as they fall. Start with the broad view to see the overall picture. Then work through the detailed images. Note especially in the 18:38 link that a detailed fine structure exists for this breaking Kelvin-Helmholtz instability wave cloud. One can see depolarization ratio 'contours' with likely ice crystal oscillation forced by turbulence near the breaking part of the wave (higher depolarization ratio). ABOUT THE IMAGES: The images are in gif format. The quick look movie is in Quick time format, and was assembled using Adobe Premiere. |