Simple Altitude Adjustments to Raindrop Velocities for Doppler Radar Analysis

Abstract

The altitude factor for adjusting raindrop velocities from sea leveldepends primarily on air density and drop size. An adjustment factoris formulated as the air density ratio raised to a power m that varieslinearly with drop diameter from 0.4 at 1 mm to 0.5 at 5 mm: m(D)= 0.375 + 0.025 D (mm). The improved velocity adjustment can be directlyincorporated into the standard equation for calculating the sizedistribution from the Doppler spectrum. An integral mean value (m/bar/)is provided to adjust sea level values of rainfall rate and mean(and mean square) Doppler velocities. The recommended value of m(bar)varies from 0.41 to 0.46 depending on application. The simplest adjustmentis obtained using 0.42 for rainfall rate and 0.45 for mean Dopplervelocity