Sack Lunch Seminar (SLS)

Mike Spall (WHOI)

Influences of Precipitation on Water Mass Transformation and
the Meridional Overturning Circulation

The influences of precipitation on the properties of water mass transformation and
the strength of the meridional overturning circulation in marginal seas are studied using
theoretical and idealized numerical models. Nondimensional equations are developed
for the temperature and salinity anomalies of deep convective water masses, making explicit their dependence on both geometric parameters such as basin area, sill depth, and latitude, as well as on the strength of atmospheric forcing. In addition to the properties of the convective water, the theory also predicts the magnitude of precipitation required to shut down deep convection and switch the circulation into the haline mode. High resolution numerical model calculations compare well with the theory for the properties of the convective water mass, the strength of the meridional overturning circulation, and also for the shutdown of deep convection. The model also shows that for precipitation levels that exceed this critical threshold, the circulation remains in a thermally direct mode even in the absence of deep convection.