Turbulent Vertical Velocities in Labrador Sea Convection

Abstract

Turbulent vertical velocity measurements are scarce in regions prone to convection such as the Labrador Sea, which hinders our understanding of deep convection dynamics. Vertical velocity, $w$, is retrieved from wintertime glider deployments in the convective region. From $w$, downward convective plumes of dense waters are identified. These plumes only cover a small fraction of the convective area. Throughout the convective area, the standard deviation of $w$ agrees with scaling relations for the atmospheric surface and boundary layers. It initially depends on surface buoyancy loss in winter, and later, on wind stress after mid-March. Both periods are characterized by positive turbulent vertical buoyancy flux. During convective periods in winter, the positive buoyancy flux is mostly forced by surface heat loss. After mid-March, when buoyancy loss to the atmosphere is reduced, the positive buoyancy flux results from a restratifying upward freshwater flux, potentially of lateral origins and without much atmospheric influence.