Assessing the benefits of specific attenuation for quantitative precipitation estimation with a C-band radar network
Ju‐Yu Chen, Silke Trömel, Alexander Ryzhkov, Clemens Simmer
Abstract
Abstract 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 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 α H for the A H estimates. The normalized raindrop concentration (N w ) 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 α H values are derived. For heavier continental rain with Z H > 40 dBZ, the AH-based rainfall retrieval R(A H ) is combined with a rainfall estimator using a substitute of specific differential phase ( ). 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 α H/V values when evaluated with gauge measurements and outperform RW when evaluated by disdrometer measurements. Potential improvements using ray-wise α H/V and segment-wise applications of the ZPHI method along the radials are discussed.