Radar-radiometer retrievals of cloud number concentration and dispersion parameter in nondrizzling marine stratocumulus

Abstract

Abstract. The retrieval of cloud microphysical properties from remote sensors is challenging. In the past, ground-based radar-radiometer measurements have been successfully used to retrieve the liquid water content profile in nondrizzling clouds but offer little constraint in retrieving other moments of the cloud particle size distribution (PSD). Here, a microphysical condensational model under steady-state supersaturation conditions is utilized to provide additional constraints to the well-established radar-radiometer retrieval techniques. The coupling of the model with the observations allows the retrieval of the three parameters of a lognormal PSD, with two of them being height dependent. Two periods of stratocumulus from the Azores are used to evaluate the novel technique. The results appear reasonable in two nondrizzling periods: continental-like number concentrations are retrieved, in agreement with the drizzle-free cloud conditions. The cloud optical depth derived from the retrieved distributions compares well in magnitude and variability with the one derived independently from a narrow field of view zenith radiometer. Uncertainties coming from the measurements are propagated to the retrieved quantities to estimate their errors. In general, errors smaller than 20% should be attainable for most parameters, demonstrating the added value of the new technique.

Remote Sensing of Droplet Number Concentration in Warm Clouds: A Review of the Current State of Knowledge and Perspectives

“…Rémillard et al () proposed a retrieval technique that is based on the combination of radar and radiometer measurements, with additional constraints being provided by a cloud condensational growth model with a lognormal cloud DSD to describe the Z profile. Rémillard et al () demonstrated that the vertical gradient of Z combined with steady state supersaturation estimates from the radar mean Doppler velocity can be used to constrain the relationship between N d and k . Subsequently, assuming that k is constant with height, they allow for N d to vary with height.…”

The Cloud-resolving model Radar SIMulator (CR-SIM) Version 3.3: description and applications of a virtual observatory

“…A fixed aspect ratio is used for each solid hydrometeor category, but for graupel and hail the empirical expression proposed by Ryzhkov et al (2011) is also available. For all model hydrometeors, the radar polarimetric variables (which depend on particle orientation) are calculated using complex scattering amplitudes from the pre-built LUTs, assuming a mean particle canting angle of 0 • (Ryzhkov, 2001) with a choice of the particle orientation distribution. The possible choices for the distribution of particle orientations are fully (three-dimensional) random orientation, random orientation in the horizontal plane, and a two-dimensional axisymmetric Gaussian distribution of orientations.…”

Evaluation of autoconversion and accretion enhancement factors in general circulation model warm-rain parameterizations using ground-based measurements over the Azores

“…Note the differences of the reflectivity thresholds used here and in other studies. For example, these were −15 dBZ in Sauvageot and Omar (1987), −17 dBZ in Frisch et al (1995), −19 to −16 dBZ in Wang and Geerts (2003), and −30 dBZ or lower in Kollias et al (2011). The threshold used in this study is set at the cloud base rather than for the entire cloud layer as in the abovementioned studies.…”