The Influence of Thermodynamic Phase on the Retrieval of Mixed-Phase Cloud Microphysical and Optical Properties in the Visible and Near-Infrared Region

Abstract

Cloud microphysical and optical properties are inferred from the bidirectional reflectances simulated for a single-layered cloud consisting of an external mixture of ice particles and liquid droplets. The reflectances are calculated with a rigorous discrete ordinates radiative transfer model and are functions of the cloud effective particle size, the cloud optical thickness, and the values of the ice fraction in the cloud (i.e., the ratio of ice water content to total water content). In the present light scattering and radiative transfer simulations, the ice fraction is assumed to be vertically homogeneous; the habit (shape) percentage as a function of ice particle size is consistent with that used for the Moderate Resolution Imaging Spectroradiometer (MODIS) operational (Collection 4 and earlier) cloud products; and the surface is assumed to be Lambertian with an albedo of 0.03. Furthermore, error analyses pertaining to the inference of the effective particle sizes and optical thicknesses of mixed-phase clouds are performed. Errors are calculated with respect to the assumption of a cloud containing solely liquid or ice phase particles. The analyses suggest that the effective particle size inferred for a mixed-phase cloud can be underestimated (or overestimated) if pure liquid phase (or pure ice phase) is assumed for the cloud, whereas the corresponding cloud optical thickness can be overestimated (or underestimated).2

Simulations of Infrared Radiances over a Deep Convective Cloud System Observed during TC4: Potential for Enhancing Nocturnal Ice Cloud Retrievals

“…An effective radius r e of 10 µm with a gamma particle size distribution following Mishchenko and Travis [50] is used for the water cloud bulk scattering properties. For mixed-phase cloud portions (Figure 8(a)), a water-phase mixing ratio γ is defined by LWC/(IWC + LWC) first, then the bulk scattering properties of mixed-phase clouds are derived by combining those of the ice and water clouds [58][59][60][61].…”

Cloud thermodynamic phase inferred from merged POLDER and MODIS data

“…With these considerations, the ratio of SWIR/VIS reflectances can provide useful information on the cloud thermodynamic phase when the optical thickness is greater than about 1 (King et al, 2004) and as long as the cloud is not composed of internally mixed ice and liquid particles (Lee et al, 2006). As illustrated in the following section, an obvious limitation of this metric is that separation between ice and liquid phase can be ambiguous when the particle size becomes too large for liquid clouds or too small for ice clouds.…”

Retrieving the Polar Mixed‐Phase Cloud Liquid Water Path by Combining CALIOP and IIR Measurements

“…Moreover, the cloud horizontal inhomogeneity can result in so-called 3-D radiative transfer effects, such as illumination and shadowing effects in visible/near infrared band (Várnai & Marshak, 2002;Zhang et al, 2012;Zhang & Platnick, 2011), which introduce biases in LWP retrievals. Besides those factors, previous studies have shown that the single-phase assumption can also induce errors in the retrieved parameters when both ice and water are composed in the mixed-phase cloud (Adhikari & Wang, 2013;Lee et al, 2006).…”