{Return, Main Replica, DOE 97 IOP, Other 97 IOP case studies}
The University of North Dakota Cessna Citation aircraft sampled Nora cirrus remnants over and near the DOE CART site (CF) on 26 September 98. Several probes on the aircraft are used to determine the size, shape, and number concentration of cirrus crystals. These probes include: a DRI formvar replicator (ice crystals impact upon a 16 mm film coated with liquid plastic formvar, and when the formvar dries, a cast or replica of the ice crystal remains); a DRI video cloudscope (ice crystals impact upon a 5 mm diameter sapphire window and are imaged with a video microscope. The window is heated by adiabatic compression at the stagnation point, and/or by an internal heater to sublimate ice crystals); PMS 1D, 2DC and 2DP optical array probes (a linear array of 32 closely spaced diodes is used to take slices of cloud particles as they pass the airplane); and a PMS FSSP probe (forward scattering in a narrow cone from particles is measured and converted to a particle size). Replica and cloudscope images are processed at a digital image analysis laboratory at DRI. The replica movie shows full screen images of film that have ice crystals from Nora on them. This movie shows the replica and surrounding film largely as they appear during analysis. It is immediately apparent from this movie that many ice crystals are quite optically perfect hexagonal plates and columns. By comparison, much of the previous cirrus we have studied does not contain such optically perfect crystals (take a look for yourself). The observed crystal habits are determined from some combination of the ice crystal nucleation mechanism, and the air temperature and water vapor content. Crystals are nucleated, grow, and fall into lower clouds or dry regions where they sublimate. The pristine crystal habits and sizes are very consistent with the lidar depolarization images by Sassen's group. Note that not all of the crystal are perfect hexagonal plates or columns - many and usually the larger fraction are polycrystals of the plate variety. The polycrystals should give relatively strong depolarization signatures. 2DC concentrations and mean diameters as a function of aircraft altitude were computed by Mike Poellot at the University of North Dakota. ABOUT THE IMAGES: The movie contains still images that were originally in the TIFF format. The movie was assembled using photo JPEG compression to make it reasonably sized. In the detailed replica time intervals, the replica images are in JPEG format, the plots showing size distributions are in GIF format, and the PMS 2DC images are in adobe PDF format. The pms images and size distributions were prepared using DRI analysis software. |