Impact of Ice Cloud Microphysics on Satellite Cloud Retrievals and Broadband Flux Radiative Transfer Model Calculations

Abstract

Ice cloud particles exhibit a range of shapes and sizes affecting a cloud’s single-scattering properties. Because they cannot be inferred from passive visible/infrared imager measurements, assumptions about the bulk single-scattering properties of ice clouds are fundamental to satellite cloud retrievals and broadband radiative flux calculations. To examine the sensitivity to ice particle model assumptions, three sets of models are used in satellite imager retrievals of ice cloud fraction, thermodynamic phase, optical depth, effective height, and particle size, and in top-of-atmosphere (TOA) and surface broadband radiative flux calculations. The three ice particle models include smooth hexagonal ice columns (SMOOTH), roughened hexagonal ice columns, and a two-habit model (THM) comprising an ensemble of hexagonal columns and 20-element aggregates. While the choice of ice particle model has a negligible impact on daytime cloud fraction and thermodynamic phase, the global mean ice cloud optical depth retrieved from THM is smaller than from SMOOTH by 2.3 (28%), and the regional root-mean-square difference (RMSD) is 2.8 (32%). Effective radii derived from THM are 3.9 μm (16%) smaller than SMOOTH values and the RMSD is 5.2 μm (21%). In contrast, the regional RMSD in TOA and surface flux between THM and SMOOTH is only 1% in the shortwave and 0.3% in the longwave when a consistent ice particle model is assumed in the cloud property retrievals and forward radiative transfer model calculations. Consequently, radiative fluxes derived using a consistent ice particle model assumption throughout provide a more robust reference for climate model evaluation compared to ice cloud property retrievals.

Microphysical properties and fall speed measurements of snow ice crystals using the Dual Ice Crystal Imager (D-ICI)

“…8). Most of the rimed needles on that day seemed to be agglomerates or ensembles of two or more single needles (called bundles of needles by Magono and Lee, 1966). Figure 9 shows examples of double-exposed images from the side view, showing the falling ice particles twice, used to determine fall speed.…”

“…Kuhn and S. Vázquez-Martín: Snow ice crystal measurements (see, e.g. Yang et al, 2008;Baum et al, 2011;Xie et al, 2011;Loeb et al, 2018).…”

Measuring Global Ocean Heat Content to Estimate the Earth Energy Imbalance

“…Separating EEI variations generated by anthropogenic GHG emissions from other sources of EEI variations is even more difficult because the EEI response to GHG emissions is a small long term variation (of a few tenth of Wm −2 over decades to centuries) buried in the monthly to interannual noise generated by the natural variability. The typical amplitude of EEI variations at monthly to interannual time scales generated by the natural variability is on the order of ±2 Wm −2 (Loeb et al, 2018b). Recent estimates of EEI on decadal time scales suggest that the EEI response to anthropogenic GHG and aerosol emissions is 0.4-1 Wm −2 (Llovel et al, 2014;Trenberth et al, 2014;Wild et al, 2014;Smith et al, 2015;von Schuckmann et al, 2016).…”

A Review of Ice Cloud Optical Property Models for Passive Satellite Remote Sensing

“…Edition 4 keeps the particle shape and particle size distributions the same, while applying surface roughness to the particle model. The planned Edition 5 may use a two-habit model [126]. Figure 11 schematically depicts the CERES Edition 2 through five particle models.…”