Impact of 1/8 degrees to 1/64 degrees resolution on Gulf Stream model - data comparisons in basin-scale subtropical Atlantic Ocean models

We investigate the impact of 1/8 degrees, 1/16 degrees, 1/32 degrees, and 1 /64 degrees ocean model resolution on model-data comparisons for the Gulf S tream system mainly between the Florida Straits and the Grand Banks. This i ncludes mean flow and variability, the Gulf Stream pathway, the associated nonlinear recirculation gyres, the large-scale C-shape of the subtropical g yre and the abyssal circulation. A nonlinear isopycnal, free surface model covering the Atlantic from 9 degrees N to 47 degrees N or 51 degrees N, inc luding the Caribbean and Gulf of Mexico, and a similar 1/16 degrees global model are used. The models are forced by winds and by a global thermohaline component via ports in the model boundaries. When calculated using realist ic wind forcing and Atlantic model boundaries, linear simulations with Munk western boundary layers and a Sverdrup interior show two unrealistic mean Gulf Stream pathways between Cape Hatteras and the Grand Banks, one proceed ing due east from Cape Hatteras and a second one continuing northward along the western boundary until forced eastward by the regional northern bounda ry. The northern pathway is augmented when a linear version of the upper oc ean global thermohaline contribution to the Gulf Stream is added as a Munk western boundary layer. A major change is required to obtain a realistic pa thway in nonlinear models, Resolution of 1/8 degrees is eddy-resolving but mainly gives a wiggly version of the linear model Gulf Stream pathway and w eak abyssal flows except for the deep western boundary current (DWBC) force d by ports in the model boundaries. All of the higher resolution simulation s show major improvement over the linear and 1/8 degrees nonlinear simulati ons. Additional major improvement is seen with the increase from 1/16 degre es to 1/32 degrees resolution and modest improvement with a further increas e to 1/64 degrees. The improvements include (1) realistic separation of the Gulf Stream from the coast at Cape Hatteras and a realistic Gulf Stream pa thway between Cape Hatteras and the Grand Banks based on comparisons with G ulf Stream pathways from satellite IR and from GEOSAT and TOPEX/Poseidon al timetry (but 1/32 degrees resolution was required for robust results), (2) realistic eastern and western nonlinear recirculation gyres (which contribu te to the large-scale C-shape of the subtropical gyre) based on comparisons with mean surface dynamic height from the generalized digital environmenta l model (GDEM) oceanic climatology and from the pattern and amplitude of se a surface height (SSH) variability surrounding the eastern gyre as seen in TOPEX/Poseidon altimetry, (3) realistic upper ocean and DWBC transports bas ed on several types of measurements, (4) patterns and amplitude of SSH vari ability which are generally realistic compared to TOPEX/Poseidon altimetry, but which vary from simulation to simulation for specific features and whi ch are most realistic overall in the 1/64 degrees simulation, (5) a basin w ide explosion in the number and strength of mesoscale eddies (with warm cor e rings (WCRs) north of the Gulf Stream, the regional eddy features best ob served by satellite IR), (6) realistic statistics for WCRs north of the Gul f Stream based on comparison to IR analyses (low at 1/16 degrees resolution and most realistic at 1/64 degrees resolution for mean population and ring s generated/year; realistic ring diameters at all resolutions), and (7) rea listic patterns and amplitude of abyssal eddy kinetic energy (EKE) in compa rison to historical measurements from current meters. Published by Elsevier Science B.V.