Continuum sea ice rheology determined from subcontinuum mechanics

A method is presented to calculate the continuum‐scale sea ice stress as an imposed, continuum‐scale strain‐rate is varied. The continuum‐scale stress is calculated as the area‐average of the stresses within the floes and leads in a region (the continuum element). The continuum‐scale stress depends upon: the imposed strain rate; the subcontinuum scale, material rheology of sea ice; the chosen configuration of sea ice floes and leads; and a prescribed rule for determining the motion of the floes in response to the continuum‐scale strain‐rate. We calculated plastic yield curves and flow rules associated with subcontinuum scale, material sea ice rheologies with elliptic, linear and modified Coulombic elliptic plastic yield curves, and with square, diamond and irregular, convex polygon‐shaped floes. For the case of a tiling of square floes, only for particular orientations of the leads have the principal axes of strain rate and calculated continuum‐scale sea ice stress aligned, and these have been investigated analytically. The ensemble average of calculated sea ice stress for square floes with uniform orientation with respect to the principal axes of strain rate yielded alignment of average stress and strain‐rate principal axes and an isotropic, continuum‐scale sea ice rheology. We present a lemon‐shaped yield curve with normal flow rule, derived from ensemble averages of sea ice stress, suitable for direct inclusion into the current generation of sea ice models. This continuum‐scale sea ice rheology directly relates the size (strength) of the continuum‐scale yield curve to the material compressive strength.