A methodology for simultaneous retrieval of ice and liquid water cloud properties. Part I: Information content and case study

Abstract

This article presents a novel methodology dedicated to retrieving the optical and microphysical properties of ice and liquid water clouds simultaneously. An optimal estimation method is used to retrieve the ice water path of one ice-cloud layer and the optical thickness and droplet effective radius of up to two liquid-water cloud layers, along with rigorous uncertainties. In order to perform the retrievals, radiometric measurements in five channels ranging from the visible to the thermal infrared are utilized. The position of cloud layers is currently provided by lidar information, which narrows the retrievals to its track. In the first part of this article, theoretical information content analyses are performed under different atmospheric conditions, over an oceanic surface. This type of analysis quantifies prior to the retrievals the amount of information that should be available regarding each parameter to be retrieved and helps to identify which set of channels provides this information. It is observed that strong information can be expected for retrieving each parameter in double-layer cases, while yet stronger limitations appear in triple-layer cases. In the second part of this article, our methodology is applied to a case study. In agreement with a priori expectations, accurate retrievals of ice and liquid cloud properties are obtained. These results are later compared with the products of a single-layer retrieval method, CloudAerosol Lidar with Orthogonal Polarization (CALIOP) operational products and in situ estimates. We show that a much better consistency with the latter two is found when retrieving the properties of each layer simultaneously. However, further statistical analyses and comparisons with various operational products should be undertaken for validation of the methodology. Such results will be presented in the second part of this study.

Comparing airborne and satellite retrievals of cloud optical thickness and particle effective radius using a spectral radiance ratio technique: two case studies for cirrus and deep convective clouds

“…Forward simulations of upward radiance have been performed by 1-D radiative transfer simulations using the radiative transfer package LibRadtran 2.0 (Mayer, 2005;Emde et al, 2016), the discrete ordinate radiative transfer solver (DISORT) version 2 (Stamnes et al, 2000), and assuming ↑ M,λ for the cirrus (ci) and DCC case. η is the mean standard deviation with the subscripts "S" for SMART and "M" for MODIS.…”

“…However, studies by Hahn et al (1984) and Warren et al (1985) analyzing ground-based observations reported that the coexistence of multilayer clouds (e.g., cirrus above liquid water clouds) is found in about 50 % of the cases. Chang and Li (2005) and Sourdeval et al (2015) have demonstrated that omitting the low liquid water cloud in the retrieval algorithm introduces significant uncertainties in the retrieved cirrus properties.…”

Ice crystal number concentration estimates from lidar-radar satellite remote sensing. Part 1: Method and evaluation

“…King et al, 1998;Sourdeval et al, 2013). Direct retrievals of the vertically integrated ice water content (IWC) -the ice water path (IWP) -can also be obtained from these channels (Sourdeval et al, 2015), passive microwave sensors (Gong and Wu, 2014), or a synergy of both (Holl et al, 2014). Vertical profiles of the cloud visible extinction (α ext ), IWC and ice crystal r eff are 10 commonly provided using lidar and/or radar measurements (e.g.…”

Degree of ice particle surface roughness inferred from polarimetric observations

“…The discrepancies among climate models (Waliser et al, 2009) in terms of ice water path (IWP) indicate that the GCM parameterizations need more reliable constraints on IWP. Recent work by Sourdeval et al (2015), which includes direct retrieval of IWP, is a novel approach to this problem.…”