Abstract
Abstract. This paper presents a methodology for ice water content (IWC) retrieval from a dual-polarization side-looking X-band airborne radar. Measured IWC from aircraft in situ probes is weighted by a function of the radar differential reflectivity (Zdr) to reduce the effects of ice crystal shape and orientation on the variation in IWC – specific differential phase (Kdp) joint distribution. A theoretical study indicates that the proposed method, which does not require a knowledge of the particle size distribution (PSD) and number density of ice crystals, is suitable for high-ice-water-content (HIWC) regions in tropical convective clouds. Using datasets collected during the High Altitude Ice Crystals – High Ice Water Content (HAIC-HIWC) international field campaign in Cayenne, French Guiana (2015), it is shown that the proposed method improves the estimation bias by 35 % and increases the correlation by 4 % on average, compared to the method using specific differential phase (Kdp) alone.
Highlights
Ice water content (IWC) and its spatial distribution inside clouds are known for the significant effects they exert on the Earth’s energy budget and hydrological cycle (e.g. Stocker et al, 2013)
Lu et al (2015) conducted an extensive simulation on both millimetre- and centimetre-wavelength radar and concluded that the ice water content (IWC)–Z relationship is very sensitive to ice crystal particle size distribution (PSD) and as such is not recommended for IWC retrievals
In this paper we present a new method for assessment of IWC based on the Kdp and Zdr measurements from a sidelooking X-band airborne radar in tropical mesoscale convective systems (MCSs)
Summary
Ice water content (IWC) and its spatial distribution inside clouds are known for the significant effects they exert on the Earth’s energy budget and hydrological cycle (e.g. Stocker et al, 2013). Aside from its significant effect on the atmospheric processes, high ice water content (IWC > 1 g m−3), which is resultant from a high concentration of small ice crystals in tropical mesoscale convective systems, has been linked to aircraft incidents and accidents (Lawson et al, 1998; Mason et al, 2006; Grzych and Mason, 2010; Strapp et al, 2016). In conventional single-polarization Doppler radar, measured radar reflectivity and radial velocity are used to assess cloud and precipitation spatial variability, precipitation rate, and characteristic hydrometeor types. The intrinsic backscattering properties of the hydrometeors for the two polarization states enable the characterization of microphysical properties such as size, shape, and spatial orientation of the cloud/precipitation particles in the radar resolution volume. Polarimetric backscattering properties of hydrometeors depend on many factors such as radar wavelength, radar elevation angle, particle size, shape, orientation, etc. We summarize how the differential reflectivity (Zdr, dB) and the specific differential phase (Kdp, ◦ km−1) are measured by a polarimetric Doppler radar in the Rayleigh scattering regime and at low radar elevation angles
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