Preprints
https://doi.org/10.5194/egusphere-2022-1099
https://doi.org/10.5194/egusphere-2022-1099
 
18 Oct 2022
18 Oct 2022
Status: this preprint is open for discussion.

Effects of including the adjoint sea ice rheology on estimating Arctic ocean-sea ice state

Guokun Lyu1, Armin Koehl2, Xinrong Wu3, Meng Zhou1, and Detlef Stammer2 Guokun Lyu et al.
  • 1Shanghai Key Laboratory of Polar Life and Environment Sciences, School of Oceanography, Shanghai Jiao Tong University, Shanghai, China
  • 2Center for Earth System Research and Sustainability (CEN), University of Hamburg, Hamburg, Germany
  • 3Key Laboratory of Marine Environmental Information Technology, National Marine Data and Information Service, Tianjin, China

Abstract. The adjoint technique has been applied to the coupled ocean and sea ice models for sensitivity studies and Arctic state estimation. However, the accuracy of the adjoint model is degraded by simplifications on the adjoint of the sea ice model, especially adjoint sea ice rheology. As part of ongoing developments of coupled ocean and sea ice estimation system, we incorporate and stabilize the adjoint of viscous-plastic sea ice dynamics (adjoint-VP) and compare it with the adjoint of a free drift sea ice model (adjoint-FD) through assimilation experiments. Using the adjoint-VP resulted in a further cost reduction of 7.9 % in comparison to adjoint-FD with noticeable improvements in ocean temperature over the open water and intermediate layers of the Arctic Ocean. Adjoint-VP more efficiently adjusts uncertain parameters than adjoint-FD by involving different sea ice retreat processes. For instance, adjoint-FD melts sea ice up to 1.0 m in the marginal seas from May to June through over-adjusting air temperature (>8 °C); adjoint-VP reproduces the sea ice retreat with smaller adjustments on the atmospheric state within the prior uncertainty range. The developments of the adjoint model here lay the foundation for further improving Arctic ocean and sea ice estimation through comprehensively adjusting the initial conditions, atmosphere forcings, and model parameters.

Guokun Lyu et al.

Status: open (until 23 Dec 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1099', Anonymous Referee #1, 07 Nov 2022 reply
  • RC2: 'Comment on egusphere-2022-1099', Anonymous Referee #2, 06 Dec 2022 reply

Guokun Lyu et al.

Guokun Lyu et al.

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Short summary
Data assimilation techniques are important for combining observations with numerical models. Here, we improve the adjoint of full sea ice dynamics (adjoint-VP) to replace the simplified adjoint of a free-drift (adjoint-FD) sea ice dynamic for developing an advanced Arctic ocean and sea ice modeling and adjoint-based assimilation system. We find that adjoint-VP provides a better ocean and sea ice estimation than adjoint-FD, considering the residual errors and adjustments of the atmosphere state.