Raindrop sorting induced by vertical drafts in convective clouds

Evidence of raindrop sorting induced by a convective updraft is presented. Using a vertically pointing 94-GHz Doppler radar (lambda = 3.2 mm) and capi talizing on the resonant nature of the backscattering cross-section as a fu nction of the raindrop size (Mie scattering), the vertical air motions to a n accuracy of 0.1 ms(-1), and the shape of the raindrop size distribution a re retrieved from the Doppler spectra. The interaction of vertical drafts a nd raindrops is documented for the first time by high resolution radar data . The updraft structure clearly causes horizontal and vertical sorting of t he raindrops. In the updraft core, small raindrops (D less than or equal to 1.7 mm) that have terminal velocities less than the updraft velocities (6- 7 ms(-1)) and a clear absence of drops greater than or equal to 3 mm are ob served. Towards the updraft periphery, a gradual increase in the raindrop s izes is documented where large raindrops (D greater than or equal to 3 mm) are observed. The observations demonstrate the importance of updrafts in di stributing the raindrops in space.