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Testing the Drop-Size Distribution Based Separation of Stratiform and Convective Rain Using Radar and Disdrometer Data from a Mid-latitude Coastal Region
* 1 , 1 , 2 , 2, 3 , 3
1  Department of Electrical and Computer Engineering, Colorado State University, Fort Collins, CO 80523, USA
2  NASA GSFC Wallops Flight Facility, Wallops Island, VA 23337, USA
3  Science Systems and Applications, Inc., Lanham, MD 20706, USA


Stratiform and convective rain are associated with different microphysical processes and generally produce drop size distributions (DSDs) with different characteristics. Identification of these two rain types is also important for estimating rainfall rates from ground-based polarimetric radars as well as spaceborne radars. Previous studies have investigated DSD characteristics using disdrometer data along with radar observations and/or vertically pointing Doppler radar observations. One such study, using data from Darwin, Australia (a tropical coastal location), found that the two rain types could be separated in the NW – Dm space, where Dm is the mass-weighted mean diameter and NW is the normalized intercept parameter. Since then, the separation method has been tested using data and observations from Greeley, Colorado, a mid-latitude continental location with semi-arid climate, and Huntsville, Alabama, a sub-tropical continental location. In this paper, we investigate the same separation technique using data and observations from a mid-latitude coastal region, situated in the Delmarva peninsula in Virginia at NASA Wallops Flight Facility (WFF). Two different types of disdrometers were used to construct the full DSD spectra and the NW versus Dm based classification is compared with simultaneous observations from a S-band polarimetric radar 38 km away from the disdrometer site. Three-minute DSDs were used for the classification and RHI (range-height indicator) radar scans over the disdrometer were used for validation. Events which occurred on 14 and 16 October 2019 were chosen. Results show, surprisingly, that there was no need to modify the separation criteria from those used in Darwin, AU. Also considered were the outer rain bands of Hurricane Dorian (as Category-1) which occurred on 06 September 2019. However, in this case, it was largely stratiform rain during the major part of the storm affecting WFF. Scattering (T-matrix) calculations using the 3-minute DSD spectra were used to derive retrieval equations for NW and Dm for the S-band radar data. These were applied to the radar scans to identify convective and stratiform rain regions as well as mixed or transition regions. Chosen RHI scans from two events (14 October 2019 and 06 September 2019) will be used as illustrative examples. Vertical profiles of reflectivity, differential reflectivity and copolar correlation coefficient over the disdrometer site will be extracted to establish whether or not the melting layer can be clearly distinguished. Specific times will be chosen from the two events and compared against the disdrometer data based classification as well for those corresponding times.

Keywords: stratiform rain; convective rain; drop size distributions; disdrometers; S-band polarimetric radar
Comments on this paper
Anthony Lupo
Intersting work
I enjoyed seeing your results and comparing some of these to one of our research groups here at the University of Missouri.
Merhala Thurai
Thank you for your comments. If there are related publications from the University of Missouri research groups, I would appreciate the references. We will continue the testing and evaluation of the method, and also explore the possibility of separating the stratiform and convective rain in terms of two (yet to be evaluated) DSD moments.