P13.16 Drop Shape Studies in Rain Using 2-d Video Disdrometer and Dual-wavelength, Polarimetric Cp2 Radar Measurements in South-east Queensland, Australia

The shape of rain drops has been studied in various ways over the past several decades, amongst them being (i) wind-tunnel measurements by Pruppacher and Beard (1970), (ii) numerical modelling of equilibrium drop shapes by Beard and Chuang (1987) and (iii) laboratory measurements by Beard et al. (1991) as well as Andsager et al. (1999). More recently, it has been shown that with a fully calibrated 2-D video disdrometer (2DVD; Schönhuber et al., 2008) it is possible to determine shape, orientation and fall velocity of individual hydrometeors falling through its 10 cm by 10 cm sensor area (Thurai and Bringi, 2005; Thurai et al. 2007a; Huang et al. 2008). The instrument has also been used in intercomparison studies with C-band polarimetric radars in various locations such as Okinawa (Bringi et al. 2006), Toronto (Thurai et al., 2007b) and Alabama (Thurai et al. 2009). In the latter, drop-by-drop information (Deq, shape and orientation) from the 2DVD was utilized to compute the individual scattering contributions from which the C-band polarimetric radar parameters such as differential reflectivity (Zdr), specific differential propagation phase (Kdp) and the co-polar correlation coefficient (ρco) were calculated. Comparisons with radar measurements indicated that significant variation in drop shapes can occur at times (i.e. under certain conditions) from the mean or the ‘mostprobable’ shapes.