WHY IS THIS CASE STUDY INTERESTING?

{Return, Main Replica, DOE 97 IOP, Other 97 IOP case studies}

CONTRIBUTORS

Pat Arnott, Rebecca Cole, T. J. Ulrich	Desert Research Institute	Cloud microphysics, web site, satellite images
Mike Poellot	Univ. North Dakota	Cloud microphysics
Ken Sassen, Jennifer Barnet	Univ. Utah	Lidar, coordination
Jay Mace	Univ. Utah	Satellite images, dynamics, radar
Kuo-Nan Liou	UCLA	Radiative transfer
Yoshidi Takano	UCLA	Single particle scattering

The in flight notes by Pat Arnott are one clue that this is an interesting cloud.

This flight proved to be one of the most interesting cirrus flights I have ever been on. The cirrus at first was fibrous, with many fall streaks. As the flight progressed, the cirrus thickened to form a dense, somewhat multilayered deck. I saw more beautiful halos, sundogs, arcs, and subsuns than ever. The halos were mostly 22 deg., though a 46 deg. partial ring was noticed on one leg. The 22 deg. halo had a companion oval halo around it (circumscribed) that touched the 22 deg halo on the top and bottom, and bulged out from it at the sides. These halos were very colorful! The interior of the halos were quite noticably darker than the outsides, consistent with angle of minimum deviation, rainbow like optics that should occur on great halos. These images are forever burned into my memory - I couldn't take my eyes off of them. Unfortunately, I left my camera at home!!! This is an error I will not repeat. If ever there was a cloud that could be modeled using classical hexagonal plate and column models, this may be IT. Looking up, I could see the glints off of layers of plate crystals screaming by above the aircraft. The flight was about 4 hours, I obtained replica for one hour before the tape ran out. The cloudscope worked great for the entire flight. Post flight analysis of the replica indicated that the film quality was excellent. This should be a great case study. I only wish that we could have gone right back out to do more sampling of these unusual clouds (if there is such a thing as a usual cloud.) I suspect that the cirrus was remnants of hurricane Nora, but will have to look at the full back trajectory to verify this. I couldn't have asked for a better send off from my 'tour of duty' at this IOP. John Hallett takes over from here. POST IOP COMMENTS: Observers in both Salt Lake City UT and at the CART site in Oklahoma reported that the remnants of hurricane Nora produced strong optical displays as it crossed the continental US. The lower lidar depolarization ratio values observed both in Utah and in Oklahoma support these observations, as do the in situ ice crystals observed in Oklahoma. Key issues are: What made this cirrus so different from 'normal' midlatitude varieties, and why did the microphysical character of the remnants maintain as it crossed the US? Suppose you wanted to model the development of cirrus clouds from nucleation to prediction of crystal habit: Over what sort of range should your model extend? This cirrus indicates that the range is of the continental to global scale. The location and mechanisms that produced this cirrus set the microphysical character of this cloud system that then advected across the continent.