Search for: All records

Recent studies revealed that scattering calculations at weather radar frequencies using individual drop shapes result in better agreement between simulated and measured polarimetric weather radar parameters, than if established rotational symmetric shape models are used. In the present work, thousands of individual rain drops that were detected with a 2D Video Disdrometer during a tropical storm, were reconstructed and their individual radar cross sections (RCS) were calculated by automatizing a commercial EM solver software. The calculations were carried out at the common weather radar frequencies at 2.8 GHz and 5.625 GHz, both for horizontal and vertical polarization. It is evaluated to what extend the RCS can differ for drops with an equal volume, it is discussed how the scattering parameters of individual drops scale within S- and C-band frequencies, and it is shown for one sample drop what effect the modelling granularity has on determined radar cross section values. 

On 9 September 2019, rain-bands of category-1 Hurricane Dorian passed over a ground instrumentation site in Delmarva peninsula, USA. Drop shapes derived from 2D Video Disdrometer measurements at this site were used to compute the S-band radar cross sections (RCS) for horizontal and vertical polarizations for each drop with equi-volume diameter > 2 mm. These are combined with RCS for the smaller drops assuming equilibrium shapes. Radar reflectivity (Zh ) and differential reflectivity (Zdr ) are calculated for each of the 3 minutes throughout the event which lasted for more than 8 hours. These are compared with simultaneous observations from an S-band polarimetric radar 38 km away. The comparisons highlight the impact of large amplitude drop oscillations on Zdr 

Tropical storm Nate, which was a powerful hurricane prior to landfall along the US Gulf coast, traversed north and weakened considerably to a tropical depression as it moved near an instrumented site in Hunstville, AL. The outer rain bands lasted 18 h (03:00 to 21:00 UTC on 08 October 2017) and a 2D-video disdrometer (2DVD) captured the event which was shallow at times and indicative of pure warm rain processes. The 2DVD measurements are used for 3D reconstruction of drop shapes (including the rotationally asymmetric drops) and the drop-by-drop scattering matrix has been computed using Computer Simulation Technology integral equation solver for drop sizes >2.5 mm. From the scattering matrix elements, the polarimetric radar observables are simulated by integrating over 1 min consecutive segments of the event. These simulated values are compared with dual-polarized C-band radar data located at 15 km range from the 2DVD site to evaluate the contribution of the asymmetric drop shapes, specifically to differential reflectivity. The drop fall velocities and drop horizontal velocities in terms of magnitude and direction, all being derived from each drop image from two orthogonal cameras of the 2DVD, are also considered.