Abstract
Abstract To better simulate the seasonal evolution of sea ice in the Arctic, with particular attention to the marginal ice zone, a sea ice model of the distribution of ice thickness, floe size, and enthalpy was implemented into the Pan-arctic Ice–Ocean Modeling and Assimilation System (PIOMAS). Theories on floe size distribution (FSD) and ice thickness distribution (ITD) were coupled in order to explicitly simulate multicategory FSD and ITD distributions simultaneously. The expanded PIOMAS was then used to estimate the seasonal evolution of the Arctic FSD in 2014 when FSD observations are available for model calibration and validation. Results indicate that the simulated FSD, commonly described equivalently as cumulative floe number distribution (CFND), generally follows a power law across space and time and agrees with the CFND observations derived from TerraSAR-X satellite images. The simulated power-law exponents also correlate with those derived using MODIS images, with a low mean bias of –2%. In the marginal ice zone, the modeled CFND shows a large number of small floes in winter because of stronger winds acting on thin, weak first-year ice in the ice edge region. In mid-spring and summer, the CFND resembles an upper truncated power law, with the largest floes mostly broken into smaller ones; however, the number of small floes is lower than in winter because floes of small sizes or first-year ice are easily melted away. In the ice pack interior there are fewer floes in late fall and winter than in summer because many of the floes are “welded” together into larger floes in freezing conditions, leading to a relatively flat CFND with low power-law exponents. The simulated mean floe size averaged over all ice-covered areas shows a clear annual cycle, large in winter and smaller in summer. However, there is no obvious annual cycle of mean floe size averaged over the marginal ice zone. The incorporation of FSD into PIOMAS results in reduced ice thickness, mainly in the marginal ice zone, which improves the simulation of ice extent and yields an earlier ice retreat.
Highlights
Significant changes have occurred in Arctic sea ice, whether in the ice pack interior (IPI) or in the marginal ice zone (MIZ) (e.g., Comiso, 2012; Strong and Rigor, 2013; Meier et al, 2014; Kwok and Cunningham, 2015; Lindsay and Schweiger, 2015)
Results indicate that the simulated floe size distribution (FSD), commonly described equivalently as cumulative floe number distribution (CFND), generally follows a power law across space and time and agrees with the CFND observations derived from TerraSAR-X satellite images
Before examining the seasonal evolution of Arctic sea ice FSD in the multicategory TFED sea ice model, model performance is assessed against Moderate Resolution Imaging Spectroradiometer (MODIS) and TerraSAR-X observations to verify that the model results are able to represent realistic natural conditions
Summary
Significant changes have occurred in Arctic sea ice, whether in the ice pack interior (IPI) or in the marginal ice zone (MIZ) (e.g., Comiso, 2012; Strong and Rigor, 2013; Meier et al, 2014; Kwok and Cunningham, 2015; Lindsay and Schweiger, 2015). The FSD equation describes changes in FSD due to ice advection, thermodynamic growth, and lateral melting It includes changes in FSD because of mechanical redistribution of floe size due largely to ocean surface wave-induced ice fragmentation and wind- and current-induced ice ridging and lead opening calculated in the ITD equation. The FSD theory, tested in a simplified ITD and FSD sea ice model with idealized numerical experiments, is able to simulate FSD that follows a power law as observed by satellites and airborne surveys (Rothrock and Thorndike, 1984; Holt and Martin, 2001; Toyota et al, 2006; Steer et al, 2008; Perovich and Jones, 2014). An examination of model results, including model validation, leads to conclusions about the seasonal evolution of sea ice in both the MIZ and IPI
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