An Investigation of the Dynamics of the East Greenland Current in Fram Strait Based on a Simple Analytical Model

Abstract

The East Greenland Current (EGC) in Fram Strait is examined in summer, based on the hydrographic data from the MIZEX 84 experiment, and its dynamics is further analyzed using a simple analytical model. From the observed density field, the southward geostrophic transport relative to the bottom in the EGC is estimated to be about 4 Sv (Sv ≡ 106 m3 s?1) at 78.4°N, which, assuming a ratio 1:1 between the bottom and the relative transports as suggested in the literature, allows one to postulate a 4 Sv bottom transport. The hydrographic data also reveal a northward gradient of potential energy along the East Greenland slope, between 77.5°N and 80.5°N. Such a gradient is the prerequisite for the existence of the joint effect of baroclinicity and relief (JEBAR), which is here proposed as a driving mechanism for the bottom transport in the EGC. A model with idealized topography and a density distribution prescribed from the above data is constructed based on a steady-state vorticity equation in which the JEBAR forcing is balanced by damping due to friction. According to the model, the JEBAR-induced flow consistent with such a gradient is southward. Validity requirements on the model assumptions constrain the range of allowable values for the model friction parameters. The prediction of a 4 Sv bottom transport can be obtained for a total amount of friction within this range. Both internal and bottom friction are considered in the model. The relative importance of these two types of friction determines to what extent the JEBAR controls the bottom or the depth-averaged flow and constrains the local characteristics of the flow. If only internal friction is allowed in the model, the required value of the friction coefficient is consistent with the values reported in the literature while, if bottom friction alone is allowed, prediction of a 4 Sv bottom transport is possible only for a relatively high friction coefficient. In terms of flow structure, the best agreement between the predicted flow and the current meter data reported in the literature is obtained for a regime with both types of friction in which, however, internal friction predominates.