Observational and Modeling Study of Ice Hydrometeor Radar Dual-Wavelength Ratios

Abstract

The influence of ice hydrometeor shape on the dual-wavelength ratio (DWR) of radar reflectivities at millimeter-wavelength frequencies is studied theoretically and on the basis of observations. Data from dual-frequency (Ka–W bands) radar show that, for vertically pointing measurements, DWR increasing trends with reflectivity Ze are very pronounced when Ka-band Ze is greater than about 0 dBZ and that DWR and Ze values are usually well correlated. This correlation is explained by strong relations between hydrometeor characteristic size and both of these radar variables. The observed DWR variability for a given level of reflectivity is as large as 8 dB, which is in part due to changes in mean hydrometeor shape as expressed in terms of the particle aspect ratio. Hydrometeors with a higher degree of nonsphericity exhibit lower DWR values when compared with quasi-spherical particles because of near-zenith reflectivity enhancements for particles outside the Rayleigh-scattering regime. When particle mass–size relations do not change significantly (e.g., for low-rime conditions), DWR can be used to differentiate between quasi-spherical and highly nonspherical hydrometeors because (for a given reflectivity value) DWR tends to increase as particles become more spherical. Another approach for differentiating among different degrees of nonsphericity for larger scatterers is based on analyzing DWR changes as a function of radar elevation angle. These changes are more pronounced for highly nonspherical particles and can exceed 10 dB. Measurements of snowfall spatiotemporally collocated with spaceborne CloudSat W-band radar and ground-based S-band operational weather radars also indicate that DWR values are generally smaller for ice hydrometeors with higher degrees of nonsphericity, which, for the same level of S-band reflectivity, exhibit greater differential reflectivity values.

Estimating total attenuation using Rayleigh targets at cloud top: applications in multilayer and mixed-phase clouds observed by ground-based multifrequency radars

“…the well-behaved backscattering properties of ocean and, to a lesser degree, land surfaces and is generally applicable to measurements from airborne and spaceborne platforms (Meneghini et al, 2000(Meneghini et al, , 2015Haynes et al, 2009). When several radar frequencies are available, differential SRT-PIA ( PIA) estimates have been proven to be even more robust than single-frequency estimates (Battaglia et al, 2016;Liao and Meneghini, 2019).…”

Ice Hydrometeor Shape Estimations Using Polarimetric Operational and Research Radar Measurements

“…Maximum observed reflectivities (Figure 7a) were approximately 5 dBZ and estimated D mv values were generally less than 1.5 mm. At these reflectivity levels, non-Rayleigh scattering effects at K a -band are expected to be rather small [32]. For larger particle populations, however, these effects could be substantial and need to be accounted for in the retrievals.…”

The ARM Radar Network: At the Leading Edge of Cloud and Precipitation Observations

“…If the two radar reflectivity measurements are from particles in the small to the wavelength scattering regime, DWR provides a path to retrieving liquid water content (LWC) in clouds without a priori knowledge of the shape of the liquid water content profile or the droplet size distribution. This approach has the additional advantage of not requiring absolutely calibrated radar reflectivity observations (e.g., Eccles and Mueller 1971;Hogan et al 2005;Huang et al 2009;Li and Moisseev 2019;Martner 1993;Matrosov et al 2019;Vivekanandan et al 1999;Zhu et al 2019) An example of DWR-based LWC in liquid clouds is discussed in the next section and details of the application of the techniques on the SACR2 are discussed in Zhu et al (2019). In very shallow clouds (less than 200 m thick), techniques that combine radar and radiometer measurements are also preferred (Küchler et al 2018).…”