Preprints
https://doi.org/10.5194/tc-2021-14
https://doi.org/10.5194/tc-2021-14

  29 Jan 2021

29 Jan 2021

Status: this preprint has been withdrawn by the authors.

Comparison of optical-equivalent snow grain size estimates under Arctic low Sun conditions during PAMARCMiP 2018

Evelyn Jäkel1, Tim Carlsen1,2, André Ehrlich1, Manfred Wendisch1, Michael Schäfer1, Sophie Rosenburg1, Konstantina Nakoudi3, Marco Zanatta3,4, Gerit Birnbaum5, Veit Helm5, Andreas Herber5, Larysa Istomina5,6, Linlu Mei6, and Anika Rohde7 Evelyn Jäkel et al.
  • 1Leipzig Institute for Meteorology (LIM), University of Leipzig, Germany
  • 2Department of Geosciences, University of Oslo, Oslo, Norway
  • 3Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), Potsdam, Germany
  • 4LISA (Laboratoire Interuniversitaire des Systèmes Atmosphériques), UMR CNRS 7583, Université Paris-Est-Créteil, Université de Paris, Institut Pierre Simon Laplace (IPSL), Créteil, France
  • 5Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), Bremerhaven, Germany
  • 6Institute of Environmental Physics, University of Bremen, Bremen, Germany
  • 7Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

Abstract. The size and shape of snow grains directly impacts the reflection by a snowpack. In this article, different approaches to retrieve the optical-equivalent snow grain size (ropt) or, alternatively, the specific surface area (SSA) using satellite, airborne, and ground-based observations are compared and used to evaluate ICON-ART (ICOsahedral Non-hydrostatic – Aerosols and Reactive Trace gases) simulations. The study is focused on low Sun and partly rough surface conditions encountered during a three-week campaign conducted North of Greenland in March/April 2018 within the framework of the PAMARCMiP (Polar Airborne Measurements and Arctic Regional Climate Model Simulation Project) project. Further, we propose an adjusted airborne retrieval method by using the albedo at 1700 nm wavelength. This reduced the effect of atmospheric masking and improved the sensitivity on ropt. From this approach we achieved a significantly improved uncertainty (< 25 %) compared to the previous method. Ground-based in situ measurements indicated an increase of ropt of 15 µm within a five-day period after a snowfall event, which is small compared to previous observations under similar temperature regimes. This low growth rate is well represented by a parametrization of snow metamorphism, when the vertical temperature gradient effect is suppressed. ICON-ART captured the observed change of ropt during snow fall events, but systematically overestimated the snow grain growth by about 100 %. Satellite-based and airborne retrieval methods showed higher and more variable ropt-values over sea ice (< 300 µm) than over land surfaces (< 100 µm), which could partly be attributed to the impact of surface roughness on the retrieval. Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals revealed a large spread within a series of subsequent individual overpasses, indicating their limitations in observing the snow grain size evolution in early spring conditions with low Sun.

This preprint has been withdrawn.

Evelyn Jäkel et al.

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Evelyn Jäkel et al.

Evelyn Jäkel et al.

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This preprint has been withdrawn.

Short summary
Different approaches to retrieve the optical-equivalent snow grain size using satellite, airborne, and ground-based observations were evaluated and compared to modeled data. The study is focused on low Sun and partly rough surface conditions encountered North of Greenland in March/April 2018. We proposed an adjusted airborne retrieval method to reduce the retrieval uncertainty.