An instability theory of ice‐air interaction for the formation of ice edge bands

Abstract

Ice edge bands are well‐observed phenomena at the ice edge of the world ocean at times when winds are blowing off the ice. Differing from the wave radiation theory, water wave theory, wind wave theory, and ice‐water coupling theory, we propose an ice‐air feedback mechanism to generate the ice edge bands. To eliminate ocean effects, the water is set motionless. Thermally generated surface winds, blowing from ice to water (ice breeze) with some deflection due to the earth's rotation, force the drift of ice floes in the marginal ice zone (MIZ). By changing the surface temperature gradient, the ice motion feeds back on the surface winds. A coupled ice‐air model similar to the author's earlier paper is employed to discuss the instability properties of such a feedback mechanism. The linearized governing equations are then solved as an eigenvalue problem with two model parameters: mean ice thickness Hi (0.5 m < Hi < 2.5 m) and a characteristic surface temperature difference over ice and water DT0 (4°C < DT0 < 20°C). The model results show alternating ice divergence and convergence zones and demonstrate a great number of e‐folding acceleration modes excited by the coupled ice‐air system. Ice floes are transported from the divergence area to the convergence zone and are eventually rearranged into a band structure. The e‐folding acceleration rate of ice motion depends on the width of two adjacent convergence zones l. It increases with L/l (where L is the length of twice the MIZ width, i.e., 200 km) for 10 km < l < 200 km, and then remains high for 2 km < l < 10 km. The length scale (2–10 km) of the high acceleration modes agrees well with the observed ice edge bandwidth (1–10 km). The e‐folding acceleration rate increases with an increase in DT0 and with a decrease in Hi.