A Tale of Two Cirrus
Poellot, M.R.(a), Mace, G.G.(b), and Arnott, W.P. (c), University of North Dakota (a), University of Utah (b), Desert Research Institute (c)
Twelfth Atmospheric Radiation Measurement (ARM) Science Team Meeting
On May 8, 1998, an orographically-forced cirrus layer overspread the DOE ARM Program's Southern Great Plains site and subsequently became mixed with anvil outflow from thunderstorms. These clouds were sampled in situ by the University of North Dakota Citation aircraft and remotely by an array of ground-based radar, lidar and radiometric instrumentation. The first of two aircraft flights sampled the orographic cirrus through a series of step climbs and spirals. During that time, the cloud was relatively uniform in depth and structure. Shortly after the start of the second flight, the anvil outflow arrived over the site. That cloud had a larger cellular structure, larger ice particles, and increased in depth during the second half of the mission. These differences are evident in both the aircraft and radar data. In addition, the atmosphere was fairly turbulent in the anvil where it had been mostly smooth in the orographic cirrus. The sampling profile included a step descent, spirals and a 100 km level run upwind to characterize the turbulence and cloud. A direct, detailed analysis of these cirrus clouds will be presented, including cloud microphysical properties and macrophysical structure, as determined from in situ and remote observations. This study will compare the character of the two cloud types, which had distinctly different forcing mechanisms. It will also provide a good test of remote sensing cloud property retrieval algorithms as there were no lower clouds beneath the cirrus. The performance of a cloud radar algorithm will be presented.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
