Comparison of Laboratory Ice Cloud and Cirrus Crystal Size Spectra Obtained with the FSSP and Cloudscope

Arnott, W.P., Schmitt, C.G., Lowenthal, D.H., Desert Research Institute; Poellot, M.R., University of North Dakota
Ninth Atmospheric Radiation Measurement (ARM) Science Team Meeting

Laboratory cloud chamber measurements of ice cloud particle size spectra have been performed using three methods: a Forward Scattering Spectrometer Probe (FSSP), a video impactor or cloudscope, and inversion of infrared (IR) spectral extinction measurements. The purpose is to evaluate the FSSP for use with ice crystal clouds. Results indicate generally good agreement among particle spectra when the number concentration is sufficiently low. In situ measurements of cirrus using an FSSP and cloudscope were performed during the 1997 Atmospheric Radiation Measurement (ARM) Program's Intensive Observation Period (IOP) at the Southern Great Plains (SGP) site with the University of North Dakota (UND) Citation aircraft. These measurements indicate a somewhat broader size spectra observed with the FSSP, though reasonable agreement with the cloudscope. Under conditions of relatively low concentrations of crystals larger than 50 um, the FSSP may be a reasonable instrument to use for deducing the elusive small ice crystal content of cirrus clouds.

Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).