Sensitivity analysis of DSD retrievals from polarimetric radar in stratiform rain based on the <i>μ</i>–Λ relationship
<p>Raindrop size distributions (DSDs) play a crucial role in quantitative rainfall estimation using weather radar. Thanks to dual polarization capabilities, crucial information about the DSD in a given volume of air can be retrieved. One popular retrieval method assumes that the DSD can be mod...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-08-01
|
| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/15/4951/2022/amt-15-4951-2022.pdf |
| Summary: | <p>Raindrop size distributions (DSDs) play a crucial role in quantitative rainfall estimation using weather radar. Thanks to dual polarization capabilities, crucial information about the DSD in a given volume of air can be retrieved. One popular retrieval method assumes that the DSD can be modeled by a constrained gamma distribution in which the shape (<span class="inline-formula"><i>μ</i></span>) and rate (<span class="inline-formula">Λ</span>) parameters are linked together by a deterministic relationship. In the literature, <span class="inline-formula"><i>μ</i></span>–<span class="inline-formula">Λ</span> relationships are often taken for granted and applied without much critical discussion. In this study, we take another look at this important issue by conducting a detailed analysis of <span class="inline-formula"><i>μ</i></span>–<span class="inline-formula">Λ</span> relations in stratiform rain and quantifying the accuracy of the associated DSD retrievals. Crucial aspects of our research include the sensitivity of <span class="inline-formula"><i>μ</i></span>–<span class="inline-formula">Λ</span> relations to the temporal aggregation scale, drop concentration, inter-event variability, and adequacy of the gamma distribution model. Our results show that <span class="inline-formula"><i>μ</i></span>–<span class="inline-formula">Λ</span> relationships in stratiform rain are surprisingly robust to the choice of the sampling resolution, sample size, and adequacy of the gamma model. Overall, the retrieved DSDs are in a rather decent agreement with ground observations (correlation coefficient of 0.57 and 0.74 for <span class="inline-formula"><i>μ</i></span> and <span class="inline-formula"><i>D</i><sub>m</sub></span>). The main sources of errors and uncertainty during the retrievals are calibration offsets in reflectivity (<span class="inline-formula"><i>Z</i><sub>hh</sub></span>) and differential reflectivity (<span class="inline-formula"><i>Z</i><sub>dr</sub></span>). Measurement noise and differences in scale between radars and disdrometers also play a minor role. The raindrop concentration (<span class="inline-formula"><i>N</i><sub>T</sub></span>) remains the most difficult parameter to retrieve, which can be off by several orders of magnitude. After careful data filtering and removal of problematic <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M18" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>Z</mi><mi mathvariant="normal">hh</mi></msub><mo>/</mo><msub><mi>Z</mi><mi mathvariant="normal">dr</mi></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="39pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="3e1e5e025f5cb13bb6c81ee65a27f35b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-4951-2022-ie00001.svg" width="39pt" height="14pt" src="amt-15-4951-2022-ie00001.png"/></svg:svg></span></span> pairs, the correlation coefficient for the retrieved <span class="inline-formula"><i>N</i><sub>T</sub></span> values remained low, only slightly increasing from 0.12 into 0.24.</p> |
|---|---|
| ISSN: | 1867-1381 1867-8548 |