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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/amt-2020-253
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2020-253
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  07 Jul 2020

07 Jul 2020

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This preprint is currently under review for the journal AMT.

The development of rainfall retrievals from radar at Darwin

Robert Jackson1, Scott Collis1, Valentin Louf2, Alain Protat3, Die Wang4, Scott Giangrande4, Elizabeth J. Thompson5, Brenda Dolan6, and Scott W. Powell7 Robert Jackson et al.
  • 1Argonne National Laboratory, 9700 Cass Ave., Lemont, IL, USA
  • 2School of Earth, Atmosphere and Environment, Monash University, Clayton, VIC, Australia
  • 3Bureau of Meteorology, 700 Clayton St., Docklands, VIC, Australia
  • 4Brookhaven National Laboratory, 98 Rochester St., Upton, NY, USA
  • 5National Oceanic and Atmospheric Administration Physical Sciences Laboratory, 325 Broadway, Boulder, CO, 80305
  • 6Colorado State University, Department of Atmospheric Sciences, 3915 W Laport Ave, Fort Collins, CO 80523
  • 7Department of Meteorology, Naval Postgraduate School, Monterey, CA

Abstract. The U.S. Department of Energy Atmospheric Radiation Measurement program Tropical Western Pacific site hosted a C-band POLarization (CPOL) radar in Darwin, Australia. It provides two decades of tropical rainfall characteristics useful for validating global circulation models. Rainfall retrievals from radar assume characteristics about the droplet size distribution (DSD) that vary significantly. To minimize the uncertainty associated with DSD variability, new radar rainfall techniques use dual polarization and specific attenuation estimates. This study challenges the applicability of several specific attenuation and dual-polarization based rainfall estimators in tropical settings using a 4-year archive of Darwin disdrometer datasets in conjunction with CPOL observations. This assessment is based on three metrics: statistical uncertainty estimates, principal component analysis (PCA), and comparisons of various retrievals from CPOL data.

The PCA shows that over 99 % of the variability in estimated rainfall rate R can be explained by radar reflectivity factor for rainfall rates 1 < R <10 mmhr−1. These rates primarily originate from stratiform clouds and weak convection (median drop diameters less than 1.5 mm). The dual-polarization specific differential phase increases in usefulness for rainfall estimators in times with R > 10 mmhr−1. Rainfall estimates during these conditions primarily originate from deep convective clouds with median drop diameters greater than 1.5 mm. Using specific attenuation for estimating R generally does not provide additional skill beyond other metrics for Darwin. An uncertainty analysis and intercomparison with CPOL show that a CSU-blended technique for tropical oceans, with modified estimators developed from VDIS observations, is most appropriate for use in all cases, such as when 1 < R < 10 mmhr−1 (stratiform rain), and when R > 10 mm hr−1 (deeper convective rain).

Robert Jackson et al.

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Latest update: 08 Aug 2020
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Short summary
Four years of 2D video disdrometer data in Darwin are used to develop and validate rainfall retrievals for tropical convection in C- and X- band radars in Darwin. Using blended techniques previously used for Colorado and Manus and Gan Island, with modified coefficients in each estimator, provided the most optimal results. Using specific attenuation for developing radar estimators provided no advantage over the use of other radar observables.
Four years of 2D video disdrometer data in Darwin are used to develop and validate rainfall...
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