The Floe Size Distribution in the Marginal Ice Zone of the Beaufort and Chukchi Seas

Harry L Stern III1, Axel J B Schweiger2, Margaret Stark3, Jinlun Zhang4, Phil Byongjun Hwang5 and Michael Steele2, (1)Univ Washington, Seattle, WA, United States, (2)Applied Physics Laboratory University of Washington, Polar Science Center, Seattle, WA, United States, (3)University of Washington, Polar Science Center, Applied Physics Laboratory, Seattle, WA, United States, (4)University of Washington, Seattle, WA, United States, (5)Scottish Association for Marine Science, Oban, United Kingdom
Abstract:
In order to support the calibration and validation of our high-resolution coupled sea ice/ocean modeling and assimilation system, which now includes a floe size distribution (FSD), we have analyzed the FSD in 256 MODIS satellite images from 2013 and 2014 in the Marginal Ice Zone (MIZ) of the Beaufort and Chukchi seas. Proper characterization of the FSD is important for modeling the MIZ.

We find that the FSD (the number of floes in different size categories) obeys a power-law distribution with an exponent that varies systematically over the course of spring, summer, and fall. The exponent (or slope in log-log space) is relatively shallow in spring but becomes steeper in summer, reflecting the fact that floes break up, resulting in fewer large floes relative to the number of small floes. In late summer the slope becomes shallower again, since small floes melt more quickly than large floes.

The spatial resolution of MODIS limits our analysis to floes larger than about 1 km in diameter. To investigate smaller scales, we calculated the FSD in satellite images from radar (SAR, 50-meter resolution) and optical (MEDEA, 1-meter resolution) sensors that overlap in space and time with MODIS images, to see whether the power-law FSD in the MODIS images extends to smaller scales. We present the results of those calculations, as well as comparisons between the modeled and observed FSD.

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