Preprints
https://doi.org/10.5194/amt-2021-163
https://doi.org/10.5194/amt-2021-163

  11 Aug 2021

11 Aug 2021

Review status: this preprint is currently under review for the journal AMT.

New sampling strategy removes imaging spectroscopy solar-smearing bias in sub-km vapour scaling statistics

Mark T. Richardson1,2, David R. Thompson1, Marcin J. Kurowski1, and Matthew D. Lebsock1 Mark T. Richardson et al.
  • 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
  • 2Department of Atmospheric Science, Colorado State University, Fort Collins, CO 90095, USA

Abstract. Upcoming spaceborne imaging spectrometers will allow retrieval of total column water vapour (TCWV) over land at horizontal resolution of 30–80 m. Here we show how to obtain, from these retrievals, exponents describing the power-law scaling of sub-km horizontal variability in clear-sky bulk planetary boundary layer (PBL) water vapour (q). Using large-eddy simulations (LES) of shallow convective PBLs we show how sunlight entering the PBL up to several km away from the footprint location degrades estimates of these exponents. We address this by calculating exponents perpendicular to the solar azimuth, that is to say flying “across” the sunlight path rather than “towards” or “away” from the Sun. Across 23 LES snapshots, at SZA = 60° the mean bias in calculated exponent is 38 ± 12 % (95 % range) along the solar azimuth, while following our strategy it is 3 ± 9 % and no longer significant. Both bias and root-mean-square error RMSE decrease with lower SZA. We include retrieval errors from several sources including: (1) the Earth Surface Mineral Dust Source Investigation (EMIT) instrument noise model, (2) requisite assumptions about the atmospheric thermodynamic profile, and (3) spatially nonuniform aerosol distributions. This technique can be used to obtain unique information about sub-km PBL q scaling from upcoming spaceborne spectrometer missions, while mitigating errors due to challenging solar geometries.

Mark T. Richardson et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-163', Anonymous Referee #1, 31 Aug 2021
  • RC2: 'Comment on amt-2021-163', Anonymous Referee #2, 04 Sep 2021
    • AC1: 'Reply on RC2', Mark Richardson, 07 Sep 2021

Mark T. Richardson et al.

Mark T. Richardson et al.

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Short summary
Sunlight's diagonal path through the atmosphere "smears" the resolution of atmospheric retrievals from imaging spectroscopy. In simulations we show how calculating exclusively "across" the sunlight direction instead of "into" or "away from" the Sun removes a bias and allows sub-km information about water vapour's spatial scaling to be calculated. This approach could be tested by airborne campaigns and, if successful, used to obtain new information from upcoming spaceborne data products.