Assessing the Benefits of Specific Attenuation for Quantitative Precipitation Estimation with a C-Band Radar Network

• Published in: Journal of hydrometeorology Vol. 22; no. 10; pp. 2617 - 2631
• Main Authors: Cen, Ju-Yu, Trömel, Silke, Ryzhkov, Alexander, Simmer, Clemens
• Format: Journal Article
• Language: English
• Published: Boston American Meteorological Society 01.10.2021
• Subjects: Algorithms; Atmospheric precipitations; Attenuation; C band; Drop size; Gauges; Horizontal polarization; Meteorological services; Meteorology; Performance assessment; Polarization; Precipitation; Precipitation estimation; Quality control; Radar; Radar attenuation; Radar networks; Rain; Rain gauges; Raindrops; Rainfall; Reflectance; Superhigh frequencies; Temperature effects; Vertical polarization; Germany; Taiwan
• ISSN: 1525-755X; 1525-7541
• DOI: 10.1175/JHM-D-20-0299.1

Recent advances demonstrate the benefits of radar-derived specific attenuation at horizontal polarization (A H) for quantitative precipitation estimation (QPE) at S and X band. To date the methodology has, however, not been adapted for the widespread European C-band radars such as those installed in the network of the German Meteorological Service (DWD, Deutscher Wetterdienst). Simulations based on a large dataset of drop size distributions (DSDs) measured over Germany are performed to investigate the DSD dependencies of the attenuation parameter αH for the A H estimates. The normalized raindrop concentration (Nw) and the change of differential reflectivity (Z DR) with reflectivity at horizontal polarization (Z H) are used to categorize radar observations into regimes for which scan-wise optimized αH values are derived. For heavier continental rain with Z H > 40 dBZ, the A H-based rainfall retrieval R(A H) is combined with a rainfall estimator using a substitute of specific differential phase ( K DP * ) . We also assess the performance of retrievals based on specific attenuation at vertical polarization (A V). Finally, the regime-adapted hybrid QPE algorithms are applied to four convective cases and one stratiform case from 2017 to 2019, and compared to DWD’s operational Radar-Online-Aneichung (RADOLAN) RW rainfall product, which is based on Z h only but adjusted to rain gauge measurements. For the convective cases, our hybrid retrievals outperform the traditional R(Z h) and pure R(A H/V) retrievals with fixed αH/V values when evaluated with gauge measurements and outperform RW when evaluated by disdrometer measurements. Potential improvements using ray-wise αH/V and segment-wise applications of the ZPHI method along the radials are discussed.