07 Feb 2022
07 Feb 2022
Status: this preprint is currently under review for the journal TC.

Rain-on-Snow (ROS) Understudied in Sea Ice Remote Sensing: A Multi-Sensor Analysis of ROS during MOSAiC

Julienne Stroeve1,2,3, Vishnu Nandan1, Rosemary Willatt3, Ruzica Dadic4,5, Philip Rotosky6, Michael Gallagher7, Robbie Mallett3, Andrew Barrett2, Stefan Hendricks8, Rasmus Tonboe9, Mark Serreze2, Linda Thielke6, Gunnar Spreen6, Thomas Newman3, John Yackel10, Robert Ricker11, Michel Tsamados3, Amy Macfarlane5, Henna-Reetta Hannula12, and Martin Schneebeli5 Julienne Stroeve et al.
  • 1University of Manitoba, Centre for Earth Observation Science (CEOS), Winnipeg, Canada
  • 2University of Colorado, Cooperative Institute for Research in Environmental Science (CIRES), National Snow and Ice Data Center (NSIDC), Boulder, CO, USA
  • 3University College London, United Kingdom
  • 4Victoria University of Wellington, Antarctic Research Centre, New Zealand
  • 5WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
  • 6University of Bremen, Institute of Environmental Physics, Bremen, Germany
  • 7University of Colorado, Cooperative Institute for Research in Environmental Science (CIRES), National Oceanographic and Atmospheric Administration (NOAA) Physical Sciences Laboratory, Boulder, CO, USA
  • 8Alfred Wegener Institute, Bremerhaven, Germany
  • 9Technical University of Denmark, Copenhagen, Denmark
  • 10Department of Geography, University of Calgary, Canada
  • 11Norwegian Research Centre, Tromsø, Norway
  • 12Finnish Meteorological Institute, Helsinki, Finland

Abstract. Arctic rain-on-snow (ROS) deposits liquid water onto existing snowpacks. Upon refreezing, this can form icy crusts at the surface or within the snowpack. By altering radar backscatter and microwave emissivity, ROS over sea ice can influence the accuracy of sea ice variables retrieved from satellite radar altimetry, scatterometers, and passive microwave radiometers. During the Arctic Ocean MOSAiC Expedition, there was an unprecedented opportunity to observe a ROS event using in situ active and passive microwave instruments similar to those deployed on satellite platforms. During liquid water accumulation in the snowpack, there was a four-fold decrease in radar energy returned at Ku- and Ka-bands. After the snowpack refroze and ice layers formed, this decrease was followed by a six-fold increase in returned energy. Besides altering the radar backscatter, analysis of the returned waveforms shows the waveform shape changed in response to rain and refreezing. Microwave emissivity at 19 and 89 GHz increased with increasing liquid water content and decreased as the snowpack refroze, yet subsequent ice layers altered the polarization difference. Corresponding analysis of CryoSat-2 waveform shape and backscatter as well as AMSR2 brightness temperatures further shows the rain/refreeze was significant enough to impact satellite returns. Our analysis provides the first detailed in situ analysis of the impacts of ROS and subsequent refreezing on both active and passive microwave observations, providing important baseline knowledge for detecting ROS over sea ice and assessing their impacts on satellite-derived sea ice variables.

Julienne Stroeve et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review of tc-2021-383 by Stroeve, J., et al.', Anonymous Referee #1, 14 Mar 2022
    • AC1: 'Reply on RC1', Julienne Stroeve, 10 Apr 2022
  • RC2: 'Comment on tc-2021-383', Anonymous Referee #2, 30 Apr 2022
    • AC2: 'Reply on RC2', Julienne Stroeve, 15 Jun 2022

Julienne Stroeve et al.

Julienne Stroeve et al.


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Short summary
Impacts of rain-on-snow (ROS) on satellite-retrieved sea ice variables remains to be fully understood. This study evaluates the impacts of ROS over sea ice on active and passive microwave data collected during the 2019–20 MOSAiC expedition. Rainfall and subsequent refreezing of the snowpack significantly altered emitted and backscattered radar energy, laying important groundwork for understanding their impacts on operational satellite retrievals of various sea ice geophysical variables.