Underwater glider observations and modeling of an abrupt mixing event in the upper ocean

Abstract

An abrupt mixing event in the upper ocean is investigated in the Northwestern Mediterranean Sea using gliders, a new ocean monitoring technology, combined with regional atmospheric model outputs and mooring data. Intense winds (up to 20 m s−1) and buoyancy forcing during December 2009 induced strong vertical mixing of the upper ocean layer in the Balearic Sea. High‐resolution data from a coastal glider reveal a surface cooling of near 2 °C and the deepening of the Mixed Layer Depth (MLD) by more than 40 meters in the center of the basin. Comparisons between glider and ship‐emulated sections of hydrographic profiles show that the glider data make visible the small‐scale spatial variability of the MLD. The heat content released to the atmosphere by the upper ocean during this mixing event exceeds 1000 W m−2. A simulation from the Weather Research and Forecasting model reports values consistent with these observations. Additionally the atmospheric numerical simulation shows the development and evolution of a cyclone located south of the Balearic Islands. This cyclone is likely to be responsible for the wind intensification and the consequent air‐sea energy exchanges that occurred in the study area during this period.