Importance of small ice crystals to cirrus properties: Observations from the Tropical Warm Pool International Cloud Experiment (TWP-ICE)

Abstract

During the Department of Energy Atmospheric Radiation Measurement Program (DOE ARM) sponsored Tropical Warm Pool International Cloud Experiment (TWP-ICE), ice crystals with maximum dimensions (D) < 50 μm were measured in aged cirrus and fresh anvils by a Cloud and Aerosol Spectrometer (CAS) and a Cloud Droplet Probe (CDP). The CAS/CDP ratio of the number concentrations of droplets with 3 < D < 50 μm, N3-50, averaged 0.98 ± 0.69 in liquid clouds. However, N3-50, measured by the CAS averaged 91 ± 127 times larger than N3-50 from the CDP in ice clouds. The CAS/CDP N3-50 ratio had a correlation coefficient of 0.387 with the concentration of particles with D > 100 μm measured by the Cloud Imaging Probe, suggesting that ice crystals may have been shattering or bouncing on the CAS inlet or protruding airflow shroud enhancing N>3-50,CAS. During the Costa Rica Aura Validation Experiment N3-50,CAS measured by a CAS without an airflow shroud were an order of magnitude less than those observed during TWP-ICE. This, and estimates of the maximum shattering based on the inlet and shroud sizes, suggest that the airflow shroud used during TWP-ICE was responsible for much of the shattering or bouncing. Copyright 2007 by the American Geophysical Union.