Application of Dual-Frequency Millimeter-Wave Doppler Spectra for the Retrieval of Drop Size Distributions and Vertical Air Motion in Rain

Millimeter-Wavelength Radars: New Frontier in Atmospheric Cloud and Precipitation Research

“…Under precipitating conditions, these oscillations are apparent in the observed Doppler spectra (Fig. 8) and can be used as reference points for the retrieval of the vertical air motion and subsequently the precipitation drop size distribution (Kollias et al 2002;Firda et al 1999). Combined with centimeter-wavelength radars, 94-GHz radars can provide high spatial and temporal measurements in stratiform and convective rain (Kollias et al 2003).…”

“…In addition to retrieval of cloud kinematics using millimeter-wavelength radars, techniques for retrieving cloud, ice crystal, and drizzle particle size distributions have been developed (e.g., Gossard 1988;Gossard 1994;Hogan et al 2000;Frisch et al 1995;Babb et al 1999;Mace et al 2002;Matrosov et al 2002;O'Connor et al 2005;Sekelsky et al 1999). In certain circumstances millimeter-wavelength radar Doppler spectra can be used to estimate the microphysical composition of both phases of mixed-phase clouds (Shupe et al 2004).…”

Why Mie?

“…However, the use of a model DSD is necessary for turbulence intensity retrievals. Details of this method are discussed in Firda et al (1999) and Kollias et al (1999). The accuracy of the retrievals is discussed in the appendix.…”

“…It is our own excitement about a method of making accurate measurements of vertical air motion and coincidentally raindrop spectra in precipitation (Lhermitte 1988;Firda et al 1999;Kollias et al 1999Kollias et al , 2001) that prompts us to write this paper to expose the technique to the larger meteorological community. The remote sensing technique for the vertical motion retrieval is particularly appealing since it is based on fundamental physics without the need of a complicated transfer function other than the relationship between terminal velocity and raindrop size.…”

Improved rain rate and drop size retrievals from airborne Doppler radar

“…Another approach is to use Doppler radar to measure the reflectivity-weighted terminal fall speed of raindrops, which relates to drop size. The Doppler spectrum has been used in ground-based radar retrievals to resolve vertical air motion (Atlas et al, 1973;Firda et al, 1999;O'Connor et al, 2005), distinguish cloud from precipitation (Frisch et al, 1995;Luke and Kollias, 2013), and to understand warm rain processes (Kollias et al, 2011b, a). Unfortunately in spaceborne radar applications, the Doppler spectrum is broadened by the lateral motion of the radar platform with respect to the scattering hydrometeors (Illingworth et al, 2015), which distorts the higher moments of the Doppler spectrum; consequently, only radar reflectivity, PIA, and mean Doppler velocity measurements are useful for space-borne Doppler radar retrievals.…”