Reconciling the north–south density difference scaling for the Meridional Overturning Circulation strength with geostrophy A. A. Cimatoribus1,*, S. Drijfhout1,2, and H. A. Dijkstra3 1Global Climate Division, Royal Netherlands Meteorological Institute, De Bilt, the Netherlands 2National Oceanography Centre, Southampton, UK 3Institute for Marine and Atmospheric research Utrecht, Utrecht University, Utrecht, the Netherlands *now at: Department of Physical Oceanography, Royal Netherlands Institute for Sea Research, Den Burg, the Netherlands
Received: 27 November 2013 – Accepted: 09 December 2013 – Published: 20 December 2013
Abstract. Since the formulation of the Stommel two-box model for the
meridional overturning circulation (MOC), various theoretical and
conceptual models for the MOC emerged based on scaling the MOC
strength with the north south density difference. At the same time
the MOC should obey geostrophic balance with an east-west density
difference. Scaling with the north south density gradient seems to
violate the common assumption of geostrophic balance for the
large-scale circulation, which implies that the pressure gradient is
orthogonal to the flow. In this brief report, we report on the
results of a series of numerical simulations in an idealized ocean
basin (with a zonally periodic channel at its southern end). The
simulations performed with different surface forcing conditions
indicate that the meridional and zonal density gradients, important
for the MOC strength, are in fact related to each other through the
stratification located at the northern end of the periodic channel.
The results suggest that the water properties at the northern end of
the periodic channel play a crucial role in setting the MOC
strength, possibly explaining the sensitivity of climate models to
the conditions in this area.
Citation: Cimatoribus, A. A., Drijfhout, S., and Dijkstra, H. A.: Reconciling the north–south density difference scaling for the Meridional Overturning Circulation strength with geostrophy, Ocean Sci. Discuss., 10, 2461-2479, doi:10.5194/osd-10-2461-2013, 2013.