Nadir and Limb Viewing Observations of Polar Mesospheric Clouds from the Aeronomy of Ice in the Mesosphere (AIM) Explorer

The Cloud Imaging and Particle Size (CIPS) instrument on the AIM spacecraft is a 4-camera nadir pointed imager with a bandpass centered at 265 nm and a field of view of 120 by 80 degrees. CIPS observes Polar Mesospheric Clouds (PMCs) against the sunlit Rayleigh-scattered background. At individual polar locations approximately 5km by 5km in area, CIPS observes the same volume of air multiple times over a range of scattering angles from about 35 to 150 degrees. These multi-angle observations allow the identification and extraction of the PMC scattered radiance from the Rayleigh-scattered background. From this is obtained the ice albedo and particle size. At the summer terminator on each orbit, the Solar Occultation For Ice Experiment (SOFIE) views a common cloud volume with CIPS. SOFIE uses solar occultation in 16 channels (.3 to 5 microns) to obtain ice properties including particle size mean radius and concentration in addition to temperature, water vapor abundance, and other environmental parameters. In this talk, we discuss comparisons of the CIPS and SOFIE observations. We show that CIPS reveals significant structure along the limb path observed by SOFIE. We use SOFIE retrieved cloud parameters to make predictions of CIPS common volume-average observations and compare those to the actual CIPS data. The data show excellent correlation, but some systematic differences. We present evidence that those systematic differences are related to commonly applied assumptions regarding the shape of the particle size distribution.