SA43B-4109:
Cips (Cloud Imaging and Particle Size Experiment) Observations of a Newly Discovered Population of Very Large Ice Particles in Polar Mesospheric Clouds
Thursday, 18 December 2014
David W Rusch1, Gary E Thomas2, Amal Chandran3, Aimee W Merkel2, Jerry D Lumpe Jr4, Cora E Randall2, John J Olivero5, Scott Martin Bailey6 and James M Russell III7, (1)University of Colorado, Boulder, CO, United States, (2)Univ Colorado, Boulder, CO, United States, (3)University of Alaska Fairbanks, Anchorage, AK, United States, (4)Computational Physics, Inc., Boulder, CO, United States, (5)Embry-Riddle Aeronautical University, Daytona Beach, FL, United States, (6)VA Tech, Bradley Department of Electrical Engineering, Blacksburg, VA, United States, (7)Hampton University, Department of Atmospheric and Planetary Sciences, Hampton, VA, United States
Abstract:
Observations by the Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of Ice in the Mesosphere (AIM) satellite have demonstrated the existence of Polar Mesospheric Cloud (PMC) regions populated by particles in the size range between 60 and 100 nm (radii of equivalent volume spheres). It is known from lidar, SOFIE, and CIPS measurements that typical mean PMC particle sizes are of the order of 40-50 nm. Determination of particle sizes by CIPS is accomplished by measuring the scattering of solar radiation at various scattering angles at a spatial resolution of 25 km2. PMC with ice particles principally in this 60-100 nm range are observed in 15 to 20 % of all CIPS measurements. These very large particle (VLP) events occur over spatially coherent areas. They are generally associated with regions of low cloud albedo (brightness) and ice water content. We postulate that at least part of this VLP population exists due to the action of long-period gravity waves in the low-temperature summertime mesopause region. We demonstrate the proposed mechanism through use of the 2D Community Aerosol and Radiation Model for Atmospheres (CARMA), which simulates the evolution of ice particles over several cycles of a family of modeled gravity waves. The model results are consistent with a VLP population in the cold troughs of monochromatic gravity waves with horizontal wavelengths of 600 km and periods of 10 hours (Chandran et al., 2013).
