A self-consistent high- and low-frequency scattering model for cirrus

Abstract

This paper demonstrates that an ensemble model of cirrus ice crystals that follows observed mass-dimensional power laws can predict the scattering properties of cirrus across the electromagnetic spectrum, without the need for tailor made scattering models for particular regions of the spectrum. The ensemble model predicts a mass-dimensional power law of the following form, mass ∝ D2 (where D is the maximum dimension of the ice crystal). This same mass-dimensional power law is applied across the spectrum to predict the particle size distribution (PSD) using a moment estimation parameterization of the PSD. The PSD parameterization predicts the original PSD, using in-situ estimates (bulk measurements) of the ice water content (IWC) and measurements of the in-cloud temperature; the measurements were obtained from a number of mid-latitude cirrus cases, which occurred over the U.K. during the winter and spring of 2010. It is demonstrated that the ensemble model predicts lidar backscatter estimates, at 0.355 μm, of the volume extinction coefficient and total solar optical depth to within current experimental uncertainties, hyperspectral brightness temperature measurements of the terrestrial region (800 cm−1 - 1200 cm−1) to generally well within ±1 K in the window regions, and the 35 GHz radar reflectivity to within ±2 dBZ. Therefore, for simulation of satellite radiances within general circulation models, and retrieval of cirrus properties, scattering models, which are demonstrated to be physically consistent across the electromagnetic spectrum, should be preferred.