Variability of thermally driven circulation in an idealized basin

Abstract

Thermohaline circulation from a low resolution numerical model may show very regular variability, but the cause is not well understood yet. In this study, variability of thermally driven circulation from a depth level coordinate ocean circulation model (GFDL MOM3) has been investigated. It has been suggested that bottom geometry has important effect on the strength of the variability and the following four types of bottom geometries were considered, which are a flat bottom, a bowl shaped bottom, one with a continental shelf along the eastern wall and one with a shelf along the western all wall. The model ocean is driven by zonally uniform heat flux at the surface. Surface wind stresses are not considered. As reported in earlier studies the variability is strongest in the flat bottom case and weakest in the bowl shaped bottom case. In the flat bottom case, the interaction between eastwards zonal flow at the surface driven meridional temperature gradient and boundaries near the north-eastern corner of the basin is the key variability is formed near the north-eastern corner and circulates cyclonically over the polar region. Therefore, the bottom geometry along the eastern boundary is the most important in the generation of the variability.