Calendar Event Details

Aerocenter-Erica Dolinar

Affiliation: NRL
Event Date: Tuesday, April 27, 2021

Novel Parameterization of Ice Cloud Effective Size from Collocated CALIOP-IIR and CloudSat Retrievals

Satellite-based measurements of global ice cloud microphysical properties are sampled to develop a novel set of parameterizations that can be implemented in numerical weather prediction (NWP) models and cloud radiative forcing studies. Ice cloud optical properties (i.e., scattering and absorption) are estimated based on the effective size of the cloud particles. Historically, the ice cloud effective diameter (D_e) has been parameterized from aircraft in-situ measurements and until recently, the aircraft-measured particle sizes were subject to ice crystal shattering caused by the instrument housing. Furthermore, aircraft-based parameterizations are opportunistic in that they only represent specific types of clouds (e.g., convective anvil, tropopause topped cirrus, etc.) in regions they were sampled and, in some cases, are limited in fully resolving the entire vertical cloud layer. Breaking away from the aircraft-based parameterization paradigm, this study is the first of its kind to attempt a parameterization of D_e, as a function of temperature, ice water content (IWC), and lidar-derived extinction, from satellite-based global measurements of ice clouds. Data from both active and passive remote sensing sensors from two of NASA’s A-Train satellites, CloudSat and CALIPSO, are collected to guide globally robust parameterization development of all ice cloud types and exclusively for cirrus clouds.

Based on globally observed ice clouds from satellite, the “all-ice” cloud parameterization solves smaller (i.e., more reflective) particle sizes for relatively warm cloud layers (T > 245 K), except for cloud layers with larger IWC (> 1.0 g m^–3), when compared with the in-situ based parameterization (Wyser 1998) currently being used in the U.S. Navy’s global weather model – NAVGEM. A separate parameterization is designed specifically for cirrus clouds, defined here as those with a cloud top temperature less than –37 °C and one that does not fully attenuate the lidar signal. Compared with the in-situ based parameterization from Heymsfield et al. (2014), the new parameterization produces smaller D_e (greater than 100 μm in some cases) at temperatures greater than ~205 K, which accounts for roughly 75% of the total cirrus cloud sample. The implications of these differences in parameterized effective ice particle size will soon be tested to assess their impact on global NWP forecasts and cirrus cloud radiative forcing estimates.

Posted or updated: Thursday, April 22, 2021

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