Laboratory studies of the form and oscillations towards breakup of falling raindrops in the Mainz Vertical Wind Tunnel and holographic field measurements of microphysical precipitation properties

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Serious inconsistencies exist between measured areal rainfall and the rainfall as computed from radar observations. One suggested method to improve on the estimation is to use relationships giving rainfall rates from radar reflectivities which include the shape of the raindrops. As those millimeter size raindrops are continuously oscillating, one has to know the accurate dynamic average values of the axis ratios to be able to use them in the reflectivity rainfall rate relationship. In this study we propose to use high speed time series analysis of shapes of millimetre size drops floating in the vertical wind tunnel to achieve this goal. Of special significance are the axis ratios of the drops with equivalent diameters (Do) between 1.1 and 3 mm whose dynamic mean axis ratios are theoretically predicted to be significantly different from those for the equilibrium shape. Further we suggest for the AQUARadar field experiment (Special Observation Phase, SOP) the deployment of the University of Mainz HODAR (Holographic Droplet and Aerosol Recording) instrument for in-situ ground based measurements of rain droplet and graupel/hail grain size distributions, spatial hydrometeor distributions, and individual hydrometeor velocities. In connection with one micro rain radar (MRR) from AQUARadar-D simultaneous and spatially correlated measurements of microphysical precipitation properties and the radar return can be performed this way during SOP.