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.