An inverse modeling study in Fram Strait. Part I: dynamics and circulation |
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| Institution: | 1. Department of Chemical and Environmental Engineering, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK;2. Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK;3. GeoArktis As, Rosestien 3, N-4022 Stavanger, Norway;4. Store Norske AS, PO Box 613, NO-9171 Longyearbyen, Norway;1. IFREMER, Géosciences Marines, BP70, 29280 Plouzané, France;2. Laboratory of Géosciences Montpellier, Montpellier University, Campus Triolet cc060, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France;1. Department of Earth and Atmospheric Sciences, 3507 Cullen Blvd., University of Houston, Houston, TX 77204, USA;2. Department of Geology, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, PA 19010, USA;3. CAS Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Rd., Guangzhou 510301, China |
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| Abstract: | In order to reconstruct the circulation in the northern Greenland Sea, between 77°N and 81°N, and the exchanges with the Arctic Ocean through Fram Strait, a variational inverse model is applied to the density field observed in summer 1984 during the MIZEX 84 experiment. An estimate of the three-dimensional large-scale pressure field is obtained in which the solution is decomposed into a limited number of vertical modes and the mode amplitudes are described by piece-wise polynomials on a finite-element grid. The solution should be consistent with a frictional depth-integrated vorticity balance and with the density data. The global model parameters are tuned to ensure agreement between the retrieved geostrophic velocity and independent currentmeter data. In a companion paper (Schlichtholz and Houssais, 1999b), the same method, but without dynamical constraint, is applied to the same hydrographic dataset to perform a detailed water mass analysis and to estimate individual water mass transports.A comprehensive picture of the summer geostrophic circulation in Fram Strait is obtained in which northward recirculations in the East Greenland Current (EGC) and various recirculations from the West Spitsbergen Current (WSC) to the EGC are identified. It is suggested that the branch of the WSC following the upper western slope of the Yermak Plateau turns westward beyond 81°N and recirculates southward along the lower slope, then merging with a westward recirculating branch south of 79°N. At 79°N, a southward net transport of 6.5 Sv is found in the EGC which, combined with a northward net transport of only 1.5 Sv in the WSC, results in a fairly large outflow of 5 Sv from the Arctic Ocean to the Greenland Sea.The inverse solutions show that, in summer, the local induction of vorticity by the wind stress curl or by meridional advection of planetary vorticity should be small, so that, in the EGC and in the WSC, the vorticity balance is mainly achieved between the bottom pressure torque and dissipation of vorticity through bottom friction. A substantial barotropic flow associated with along-slope potential energy gradients is indeed identified on both sides of the strait. |
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