15 Sep 2022
15 Sep 2022
Status: this preprint is open for discussion.

Nudging allows direct evaluation of coupled climate models with in-situ observations: A case study from the MOSAiC expedition

Felix Pithan1, Marylou Athanase1, Sandro Dahlke1, Antonio Sánchez-Benítez1, Matthew D. Shupe2,3, Anne Sledd2,3, Jan Streffing1,4, Gunilla Svensson5, and Thomas Jung1,6 Felix Pithan et al.
  • 1Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), Bremerhaven/Potsdam, Germany
  • 2Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado
  • 3National Oceanic and Atmospheric Administration Physical Science Laboratoriy, Boulder, Colorado
  • 4Jacobs University Bremen, Bremen, Germany
  • 5Department of Meteorology and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 6Institute of Environmental Physics, University of Bremen, Bremen, Germany

Abstract. Comparing the output of general circulation models to observations is essential for assessing and improving the quality of models. While numerical weather prediction models are routinely assessed against a large array of observations, comparing climate models and observations usually requires long time series to build robust statistics. Here, we show that by nudging the large-scale atmospheric circulation in coupled climate models, model output can be compared to local observations for individual days. We illustrate this for three climate models during a period in April 2020 when a warm air intrusion reached the MOSAiC expedition in the central Arctic. Radiosondes, cloud remote sensing and surface flux observations from the MOSAiC expedition serve as reference observations. The climate models AWI-CM1/ECHAM and AWI-CM3/IFS miss the diurnal cycle of surface temperature in spring, likely because both models assume the snow pack on ice to have a uniform temperature. CAM6, a model that uses three layers to represent snow temperature, represents the diurnal cycle more realistically. During a cold and dry period with pervasive thin mixed-phase clouds, AWI-CM1/ECHAM only produces partial cloud cover and overestimates downwelling shortwave radiation at the surface. AWI-CM3/IFS produces a closed cloud cover but misses cloud liquid water. Our results show that nudging the large-scale circulation to the observed state allows a meaningful comparison of climate model output even to short-term observational campaigns. We suggest that nudging can simplify and accelerate the pathway from observations to climate model improvements and substantially extends the range of observations suitable for model evaluation.

Felix Pithan et al.

Status: open (until 09 Feb 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review of egusphere-2022-706', Anonymous Referee #1, 03 Oct 2022 reply
  • RC2: 'Comment on egusphere-2022-706', Anonymous Referee #2, 20 Jan 2023 reply

Felix Pithan et al.

Felix Pithan et al.


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Short summary
We compare climate model output to observations from the MOSAiC expedition in the central Arctic ocean. All models show how the arrival of a warm airmass warms the Arctic in April 2020, but two models do not show the response of snow temperature to the diurnal cycle. One model has too little liquid water and too much ice in clouds during cold days. Evaluating climate models usually requires long observational timeseries, but we here present a method that also works for short field campaigns.