Abstract
Abstract. Estimates of Arctic sea ice thickness have been available from the CryoSat-2 (CS2) radar altimetry mission during ice growth seasons since 2010. We derive the sub-grid-scale ice thickness distribution (ITD) with respect to five ice thickness categories used in a sea ice component (Community Ice CodE, CICE) of climate simulations. This allows us to initialize the ITD in stand-alone simulations with CICE and to verify the simulated cycle of ice thickness. We find that a default CICE simulation strongly underestimates ice thickness, despite reproducing the inter-annual variability of summer sea ice extent. We can identify the underestimation of winter ice growth as being responsible and show that increasing the ice conductive flux for lower temperatures (bubbly brine scheme) and accounting for the loss of drifting snow results in the simulated sea ice growth being more realistic. Sensitivity studies provide insight into the impact of initial and atmospheric conditions and, thus, on the role of positive and negative feedback processes. During summer, atmospheric conditions are responsible for 50 % of September sea ice thickness variability through the positive sea ice and melt pond albedo feedback. However, atmospheric winter conditions have little impact on winter ice growth due to the dominating negative conductive feedback process: the thinner the ice and snow in autumn, the stronger the ice growth in winter. We conclude that the fate of Arctic summer sea ice is largely controlled by atmospheric conditions during the melting season rather than by winter temperature. Our optimal model configuration does not only improve the simulated sea ice thickness, but also summer sea ice concentration, melt pond fraction, and length of the melt season. It is the first time CS2 sea ice thickness data have been applied successfully to improve sea ice model physics.
Highlights
Historical observations of sea ice thickness have been limited due to their sparse spatial and temporal coverage of, and uncertainties in, measurements
We determined an optimal region for comparing sea ice thickness between simulations with the sea ice model CICE and CS2 data by taking into account the strengths and weaknesses of both approaches
The resulting region includes most of the central Arctic, but not the area of the thickest ice north of Canada or any of the shelf seas
Summary
Historical observations of sea ice thickness have been limited due to their sparse spatial and temporal coverage of, and uncertainties in, measurements. Based on sea ice draft observations from 34 US Navy submarines, a decrease of mean autumn sea ice thickness from 2.8 to 1.6 m could be identified over the period 1975–2000 within the central Arctic Ocean (Rothrock et al, 2008). Cryosphere-focused satellite altimeters such as the NASA Ice, Cloud, and land Elevation Satellite (ICESat) and ESA CryoSat-2 (CS2) have allowed estimation of sea ice thickness across the Arctic (Giles et al, 2007, 2008; Kwok and Rothrock, 2009; Laxon et al, 2013)
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