Statistical analysis of atmospheric forcing of North Pole ice draft variations

A series of correlation experiments and regression models are used to explo re the atmospheric forcing of observed interannual variability in North Pol e ice drafts as measured by U.S. Navy submarine sonar from 1982 to 1992. Me an ice drafts as well as ice draft distributions are used in the analysis. Nearby drifting buoys are used to approximate a full 2-year motion history of the North Pole ice parcels prior to submarine underpass. Drawing from th eoretical work and empirical observation, predictors of North Pole ice draf t variation are selected which embody accumulated ice exposure to subfreezi ng air temperature, ice divergence, and patterns of ice motion. The timesca les of the predictors are based on systematic evaluations of the lag depend ence of the predictor-predictand relationships. Linear correlation of each predictor with the observed ice draft distribution shows accumulated ice ex posure to subfreezing air temperature is weakly correlated with reductions in shallow (0 to 2.5-m) drafts. Ice divergence a week prior to draft measur ement correlates most closely with the redistribution of ice drafts shallow er than 3.5 m, Ice divergence and ice deflection from its wind-forced motio n during the 6 months prior to observation correlate with deeper ice drafts (deeper than 6.8 and 4.6 m, respectively). Together, these two parameters explain mure than 80% of the variance of the observed mean ice draft. The a ccumulated ice exposure to subfreezing air temperatures colder than the 198 0-1992 mean in the 2 years prior to ice arrival at the North Pole adds litt le to an explanation of the interannual variance of the mean ice draft. The results imply that (1) a realistic formulation of sea ice dynamics is a fi rst-order priority for model simulations of ice draft and (2) North Pole ic e thickness is not a simple function of Arctic air temperature.