Impact of (seasonal) initialization on the North Atlantic circulation using a hybrid co-ordinate model

Large-scale ocean circulation in the North Atlantic consists of a sub-polar gyre and a sub-tropical gyre with Gulf Stream being the primary western boundary current at the edge of the two-gyres. The thermohaline overturning consists of a northward flow of warm water in the upper 1000-1200 m, and a southward flow of cold NADW between 1200-5000 m along with a deep water renewal in subarctic regions.

Using an hybrid model (HYCOM), the above mentioned features of the North Atlantic circulation are studied comparing long simulations obtained from four different seasonal climatological initializations. The momentum, heat and freshwater fluxes on the surface are represented by 6 hourly GFS reanalysis for all four experiments.

The impact of the initial state on maintaining robust gyres and their associated water masses is studied by examining the mean kinetic energy, T-S characteristics, circulation patterns and mixed layer depths. The variability in the annual mean strength of the boundary currents, transports and the formation or lack thereof mode waters are also analyzed.