Valerie Garnier, Mohamed Iskandarani, and Eric Chassignet, RSMAS/Univ. of Miami
The flexibility inherent in HYCOM's vertical coordinate system gives the user wide latitude in configuring the vertical structure in the model. However, the latter has a direct impact on the pressure gradient errors. Previously tests have shown that the errors are negligible for isopycnal and z coordinates whatever the bathymetry. They are also negligible with the use of terrain-following layers restricted to shallow depths. However, the errors increase with the bathymetric slopes and when deeper layers are turned into terrain-following mode. While the errors can be controlled by confining the sigma-layers to shallow depths, an alternate formulation for the baroclinic pressure gradient is proposed that will enable HYCOM to cope with steeper bathymetric slopes and deeper terrain-following coordinate surfaces. Implemented modifications will be presented as well as preliminary tests, mainly the seamount test case.