Advances in Geosciences www.adv-geosci.net 1680-7340 1680-7359 20 Observation, Prediction and Verification of Precipitation (EGU Session 2008) 2009 10.5194/adgeo-20-13-2009 http://www.adv-geosci.net/20/13/2009/ http://www.adv-geosci.net/20/13/2009/adgeo-20-13-2009.html http://www.adv-geosci.net/20/13/2009/adgeo-20-13-2009.pdf 13 18 2009-03-12 Rain microstructure retrievals using 2-D video disdrometer and C-band polarimetric radar M. Thurai merhala@engr.colostate.edu V. N. Bringi W. A. Petersen Colorado State University, Fort Collins, Colorado, USA NASA-MSFC, Huntsville, Alabama, USA Measurements using the 2-D video disdrometer (2DVD) taken during a heavy rainfall event in Huntsville, Alabama, are analysed. The 2DVD images were processed to derive the rain microstructure parameters for each individual drop, which in turn were used as input to the T-matrix method to compute the forward and back scatter amplitudes of each drop at C-band. The polarimetric radar variables were then calculated from the individual drop contribution over a finite time period, e.g., 1 min. The calculated co-polar reflectivity, differential reflectivity, specific differential propagation phase and the co-polar correlation coefficient were compared with measurements from a C-band polarimetric radar located 15 km away. An attenuation-correction method based on the specific differential propagation phase was applied to the co-polar and differential reflectivity data from the C-band radar, after ensuring accurate radar calibration. Time series comparisons of the parameters derived from the 2DVD and C-band radar data show very good agreement for all four quantities, the agreement being sometimes better than the computations using the 1-min drop size distribution and bulk assumptions on rain microstructure (such as mean shapes and model-based assumptions for drop orientation). The agreement is particularly improved in the case of co-polar correlation coefficient since this parameter is very sensitive to variation of shapes as well as orientation angles. The calculations mark the first attempt at utilizing experimentally derived "drop- by-drop" rain microstructure information to compute the radar polarimetric parameters and to demonstrate the value of utilizing the 2-D video disdrometer for studying rain microstructure under various precipitation conditions. Histograms of drop orientation angles as well as the most probable drop shapes and the corresponding variations were also derived and compared with prior results from the 80 m fall "artificial rain" experiment. Beard, K. V., Bringi, V. N., Thurai, M., and Johnson, D. B.: Modeling and measurement of the shape of raindrops, Proceedings of the 5th European Radar Conference on Meteorology and Hydrology (ERAD 2008), Helsinki, Finland, paper 7.7, 2008. Bolen, S., Bringi, V. N., and Chandrasekar, V.: An optimal area approach to intercomparing polarimetric radar rain rate algorithms with guage data, J Atmos. Oceanic Technol., 15, 605–623, 1998 Bringi, V. N. and Chandrasekar, V.: Polarimetric Doppler Weather Radar: Principles and Applications, Cambridge University Press, 636, 2001. Bringi, V. N., Thurai, M., Nakagawa, K., Huang, G. J., Kobayashi, T., Adachi, A., Hanado, H., and Sekizawa, S.: Rainfall estimation from C-band polarimetric radar in Okinawa, Japan: Comparisons with 2D-video disdrometer and 400 MHz wind profiler, J. Met. Soc. Japan, 84, 705–724, 2006. Huang, G-J., Bringi, V. N. and Thurai, M.: Orientation Angle Distributions of Drops after 80 m fall using a 2-D-Video Disdrometer, J. Atmos. Oc. Tech., 25, 1717–1723, 2008. Lee, G.-W. and Zawadzki, I.: Variability of drop size distributions: Noise and Noise filtering in Disdrometric data, J. Appl. Met., 44, 634–652, 2005. Mardia, K. V.: Statistics of Directional Data, Academic Press, New York, 1972. Petersen, W. A., Knupp, K. R., Cecil, D. J., and Mecikalski, J. R.: The University of Alabama Huntsville THOR Center instrumentation: Research and operational collaboration, extended abstract P. 8A.8, 33rd Conf. on Radar Meteor., August~2007, Cairns, Australia, 2007. Schönhuber, M., Lammer, G. and Randeu, W. L.: The 2-D-Video-Distrometer, Chapter 1 in: Precipitation: Advances in Measurement, Estimation and Prediction, edited by: Michaelides, S., Springer, 2008. ISBN: 978-3-540-77654-3, 2008. Schuur, T. J., Ryzhkov, A. V.,. Zrni\'c, D. S., and Schoenhuber, M.: Drop size distributions measured by a 2-D video disdrometer: Comparison with Dual-polarization radar data, J. Appl. Met., 40, 1019–1034, 2001. Thurai, M., Huang, G.-J., Bringi, V. N., Randeu, W. L., and Schönhuber, M.: Drop Shapes, Model Comparisons, and Calculations of Polarimetric Radar Parameters in Rain, J. Atmos. Ocean. Tech., 24(6), 1019–1032, 2007. Thurai, M., Hudak, D., and Bringi, V. N.: On the Possible Use of Co-polar Correlation Coefficient for Improving the Drop Size Distribution Estimates at C-band, J. Atmos. Oc. Tech., 25, 1873–1880, 2008