Ice clouds microphysical retrieval using 94‐GHz Doppler radar observations: Basic relations within the retrieval framework

Abstract

[1] High quality measurements of ice cloud properties from ground-and space-based sensors are key for improving our understanding of processes that affect ice cloud radiative effects and lifetime. Doppler cloud radars provide two independent measurements (reflectivity and Doppler velocity) to constrain the ice clouds microphysical retrievals. However, the retrievals are highly sensitive to the choice of the scattering forward model for non-spherical particles at millimeter-wavelengths and the selection of parameters in the mass-and velocity-size relationships, as well as to the representation of the particle size distribution (PSD). In this paper (part 1), the development of the basic relations used in the retrieval is presented. A novel approach for reducing the number of free parameters required to describe the microphysical properties of ice particles is described. The new proposed form of the mass-size relationship significantly reduces the sensitivity of the quantities of interest to the power law mass exponent, leaving only one parameter controlling mass dimensional relationship. A similar approach is adopted in the velocity calculation. In order to reduce the retrieval's dependence on the size distribution, the PSD defined for liquid-equivalent diameter is described using the concept of double moment normalization. The two normalizing quantities, mean mass-weighted diameter (D m ) and ice water content (IWC) are controlled mainly by the PSD size interval that is also an important contributor to the two Doppler observables. Both D m and IWC are generally not very sensitive to the PSD segments of the smallest and largest particles that are considered as very uncertain.Citation: Szyrmer, W., A. Tatarevic, and P. Kollias (2012), Ice clouds microphysical retrieval using 94-GHz Doppler radar observations: Basic relations within the retrieval framework,

Fingerprints of a riming event on cloud radar Doppler spectra: observations and modeling

“…The scattering model used to estimate the backscattering cross section of the snow particles is based on a two-layer spherical model introduced by Fabry and Szyrmer (1999). The uncertainties associated with this backscattering computation have been discussed in Szyrmer et al (2012). While there are several different methods to prescribe the scattering calculations of snow particles (e.g., Tyynelä et al, 2013;Hogan and Westbrook, 2014), the height evolution of the radar moments of the rimed snow mode is not very sensitive to the scattering method used.…”

“…Different options of change of particle aspect ratio accompanying the growth by riming in the model use the rime density calculated from empirical formulas (Macklin, 1962;Pflaum and Pruppacher, 1979;Heymsfield and Pflaum, 1985). The following options for the evolution of the area ratio for a given increase of the rimed fraction can be selected in the model: (i) using one of the empirical relations of mass-density-area ratio (by choosing an appropriate relation from the table in Szyrmer et al, 2012 or others), or (ii) obtained by interpolation based on rimed fraction between the values associated with the unrimed particle and graupel (as in Lin and Colle, 2011), or (iii) calculated from the assumed relation of particle geometry between area ratio and aspect ratio (e.g., Avramov et al, 2011;Jensen and Harrington, 2015).…”

Developing and Evaluating Ice Cloud Parameterizations for Forward Modeling of Radar Moments Using in situ Aircraft Observations

“…One of the main challenges to measure ice clouds by remote sensing is that the transfer functions that relate the observables (e.g., radar Doppler spectrum) to cloud properties (e.g., ice water content IWC) are not uniquely defined (Szyrmer et al 2012). To overcome this challenge, this study has two main objectives: 1) estimate a mass-size relation m(D) from a combination of in situ and radar observations and 2) investigate the effect of describing particle area A and number concentration N as functions of size D on moments of the radar Doppler spectrum.…”

G band atmospheric radars: new frontiers in cloud physics

“…Donovan andvan Lammeren, 2001;Wang and Sassen, 2002;Okamoto et al, 2003;Hogan, 2008, 2010) and radar Doppler based techniques (e.g. Matrosov et al, 2002;Mace et al, 2002;Delanoë et al, 2007;Szyrmer et al, 2012). Another approach is to use cloud radar observations at two or more frequencies, such that one of the radars has a wavelength comparable to the size of the ice particles.…”