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Mind the gap - Part 2: Improving quantitative estimates of cloud and rain water path in oceanic warm rain using spaceborne radars

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posted on 2020-12-16, 15:48 authored by Alessandro Battaglia, Pavlos Kollias, Ranvir Dhillon, Katia Lamer, Marat Khairoutdinov, Daniel Watters
The intrinsic small spatial scales and low reflectivity structure of oceanic warm precipitating clouds suggest that millimeter spaceborne radars are best suited to providing quantitative estimates of cloud and rain liquid water paths (LWPs). This assertion is based on their smaller horizontal footprint; high sensitivities; and a wide dynamic range of path-integrated attenuations associated with warmrain cells across the millimeter wavelength spectrum, with diverse spectral responses to rain and cloud partitioning. State-of-the-art single-frequency radar profiling algorithms of warm rain seem to be inadequate because of their dependence on uncertain assumptions about the rain-cloud partitioning and because of the rain microphysics. Here, high-resolution cloud-resolving model simulations for the Rain in Cumulus over the Ocean field study and a spaceborne forward radar simulator are exploited to assess the potential of existing and future spaceborne radar systems for quantitative warm-rain microphysical retrievals. Specifically, the detrimental effects of nonuniform beam filling on estimates of path-integrated attenuation (PIA), the added value of brightness temperature (TB) derived adopting radiometric radar modes, and the performances of multifrequency PIA and/or TB combinations when retrieving liquid water paths partitioned into cloud (c-LWPs) and rain (r-LWPs) are assessed. Results show that (1) Ka-and W-band TB values add useful constraints and are effective at lower LWPs than the same-frequency PIAs; (2) matched-beam combined TB values and PIAs from single-frequency or multifrequency radars can significantly narrow down uncertainties in retrieved cloud and rain liquid water paths; and (3) the configuration including PIAs, TB values and near-surface reflectivities for the Ka-band-W-band pairs in our synthetic retrieval can achieve an RMSE of better than 30 % for c-LWPs and r-LWPs exceeding 100 g m-2.

Funding

This research has been supported by the European Space Agency under the “Raincast” activity (contract no. 4000125959/18/NL/NA). The work by Alessandro Battaglia has been supported by the project Radiation and Rainfall funded by the UK National Centre for Earth Observation. This research used the ALICE high-performance computing facility at the University of Leicester.

History

Citation

Atmospheric Measurement Techniques, 13, 4865–4883, https://doi.org/10.5194/amt-13-4865-2020, 2020.

Author affiliation

Department of Physics and Astronomy

Version

  • VoR (Version of Record)

Published in

Atmospheric Measurement Techniques

Volume

13

Issue

9

Pagination

4865 - 4883

Publisher

Copernicus GmbH

issn

1867-1381

eissn

1867-8548

Acceptance date

2020-07-28

Copyright date

2020

Available date

2020-09-15

Language

English

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