Understanding the modes of the sea-ice thickness distribution: Processes and variability

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The sea-ice thickness distribution (ITD) is fundamental to understanding the heat, mass and freshwater budgets of the Arctic Ocean, plays important roles in climate feedbacks, and exerts strong control on regional primary productivity, marine navigation and surface operations. Estimates of ITD based on observations in the perennial ice zone (PIZ) nearly always exhibit a prominent mode at some thickness, hm, larger than and distinct from modal thicknesses associated with the annual freezeup and recently-opened leads. This mode has been interpreted as un-deformed multi-year ice at, or growing thermodynamically towards, its equilibrium thickness. Observations indicate significant inter-regional, annual and inter-annual variations of hm within the PIZ, over the approximate range 1 to 5 meters. This statistic of the ITD has received much less attention than other parameters, such as the mean, standard deviation and e-folding length scale of ridged ice. The results of this project will improve understanding of the variations in space and time of this ecologically and societally important measure of ice thickness.The PI hypothesizes that measurements of ice of near-modal thickness have reduced bias and random error with respect to other measures of ice thickness, thus making the mode a robust parameter of the ITD. The goal of the proposed research is to enhance understanding of the ITD, focusing on the mode hm, by producing improved estimates of space/ time variations of the ITD, and greater understanding of its role in Arctic climate. Specific objectives are (a) to test the hypothesis that the mode is robust to observational errors; (b) to document space and time variation of hm and other parameters of the ITD in the PIZ; (c) to simulate the variations of the ITD and hm as a response to prescribed forcing and compare results with observations; (d) to study the dependence of simulated ITDs on the formulation of ridging and on errors in the forcing data; and (e) to synthesize the results as a new analysis and interpretation of the ITD emphasizing hm and its variations. The study domain is the Arctic Ocean PIZ during the period 1975-2010. The timescales to be considered include inter-seasonal, inter-annual and trends, as well as physical processes acting on hours and longer.