Response to Comment Paper by Dr. Maxim A. Yurkin for 2021 JGR Paper “Evaluation of Higher‐Order Quadrature Schemes in Improving Computational Efficiency for Orientation‐Averaged Single‐Scattering Properties of Nonspherical Ice Particles”

Abstract

In Fenni et al. (2021), hereafter F21, subject of the present discussion, we evaluate several high-order quadrature schemes for accuracy and efficacy in obtaining orientation-averaged single-scattering properties (SSPs). We use our efficient scattering model MIDAS to perform electromagnetic scattering calculations to evaluate the gain in efficiency from these schemes.To better frame the discussion, we would like to recall the background of and motivations to the study reported in F21. As explained in its Introduction and acknowledged in its acknowledgments, the study is performed under a project supported by the NASA Precipitation Measurement Missions program. Our primary goal is thus to improve the quantitative retrieval of precipitation that involves solid (or mixed-phase) hydrometeors using both active and passive instruments onboard the global precipitation measurement (GPM) satellite, that is, the Ku-Ka dual-frequency precipitation radar (DPR) and GPM microwave imager (GMI) radiometer respectively. In addition to Ku and Ka bands, we also investigate the use of W-band radar, because there is one on an existing mission, CloudSat, and there will be more on planned missions, for example, EarthCare. As such, there are a few salient concerns of our study.• We are concerned with both radar and radiometer measurements. For the former, backscatter of the particles is a crucial quantity. • The scattering targets of concern (i.e., solid hydrometeors) are generally irregular and complex, without symmetry to exploit. • The radiative transfer model(s), RTMs, used for passive (radiometer) retrievals are limited to media with axially or azimuthally symmetric scattering and thus require orientation-averaged single-scattering quantities.To stay consistent in the active-passive (radar-radiometer) combined retrieval, backscatter must be orientationally averaged too. • In addition, there is a concern for computation and storage costs. The numerical solution methods reported in F21 for electromagnetic (EM) scattering, albeit at varying degrees, are all computationally demanding, meaning that they require a computer (or computers) with a substantial amount of memory and take a considerable amount of time to reach a solution. We therefore do not wish to repeatedly solve the same problem and would like to save the solution. However, even for one single orientation, it takes considerable storage space, especially for large size parameters, and the storage requirement increases proportionally with the number of orientations.