Meteorological Triggers for Deep Convection in the Greenland Sea

Abstract

Abstract We postulate that a favorable condition for deep convection just seaward of a pack ice edge within a marginal ice zone (MIZ) occurs when the direction of a cold, strong, off-ice wind is at an angle of less than 45 degrees from the ice edge, with the edge to the right looking downwind. In this situation, the Ekman transport of the ice formed in the outer MIZ will be toward the pack ice, keeping the outer MIZ clear of thick ice. Sustained rapid freezing and brine rejection will occur in the outer MIZ as the cold air blowing off the ice removes heat from the ice-free ocean surface. In the East Greenland Sea MIZ (EGSMIZ), a favorable situation for cold strong winds at the correct angle occurs when there is high pressure in the region between NE Greenland and the pole and unoccluded lows south of the EGSMIZ. This pattern occurs regularly in the EGSMIZ. On horizontal scales less than 20 km, MIZ wind stress and heat flux have large variability due to changes in surface roughness, wind speed and sea surface temperature. The pack ice edge orientation is also highly variable on small scales. Thus, dynamic and thermodynamic forcing of the ocean and the induced vertical motions vary at the small scales and may contribute to confining deep convection to very small (5 to 10 km diameter) chimneys.