IUGG 2003 Abstract

P03 The Role of Tides, Mesoscale Processes, and Bottom Topography in Energy Transfer and Mixing Tuesday, July 1 PM Location: Site B, Room 19 Presiding Chair:E. Morozov

TIME [ 1400 ] [ P03/01P/B19-001 ]

PROPAGATION OF INTERNAL SOLITON ALONG THE SHELF

Olga D. SHISHKINA(Department of Hydrophysics and Hydroacoustics, Institute of Applied Physics RAS)

John GRUE(Mechanics Division, Department of Mathematics, University of Oslo) J. Kristian SVEEN ( Mechanics Division, Department of Mathematics, University of Oslo )

There is a number of known papers studying solitary waves as almost plane waves propagating at the constant topography or under the bottom varying in the direction of propagation. This work presents the results of transformation of the solitary wave in case of transverse variation of the bottom topography resulting in a three-dimensional internal wave motion. Such conditions may take place when the solitary wave is generated by tidal internal motions at the shelf slope, and then it comes to another part of theshore with the shelf edge oriented almost normally to the region of generation of the incoming wave (The Strait of Gibraltar). Or the wave propagates along a relatively narrow estuary and interacts with its near-shore zone (The Red Sea). Phenomena observed in the laboratory experiments and their correlation withSAR images of known field features are discussed. Main attention in this work was paid to possible fluid motions at the shelf bottom caused by a passing internal wave: (i) how far these motions propagate onto the shelf; (ii) what is the range of flow velocities at the shelf; (iii) what kind of flow motions should be expected depending on the parameters of the stratification and of the passing wave. Some peculiarities of propagation of a solitary wave along a shelf in the two-layer fluid with the finite thickness of both layers has been modelled in the tank with the dimensions L:B:H = 12:0.5:1 m. The behaviour of the fluid layer above the shelf was different depending on the pycnocline’s depth. When the pycnocline was positioned just above the shelf the wave could not propagate onto the shelf and wave motion was observed within the deep part of the tank only. In this case the on-shelf flow had a pronounced horizontal character (a shear flow). In case when the pycnocline was considerably above the shelf the wave could propagate along the shelf as well. The parameters of the initial wave became different at the shelf and in the deep part of the tank. In such conditions propagation of two parts of the wave will be described by different theories. As the amplitude of the wave was of about the shelf depth this part of the incoming wave was formed further in accordance with the fully non-linear theory. And another part of the wave continued its propagation in the same form. Such a combination of two plane waves of different profiles produced intense three-dimensional wave motion at the level of the pycnocline. And longitudinal propagation of the solitary wave along the tank transformed to the transverse wave motion with the less wavelength. In case when the wave amplitude was greater than the fluid depth at the shelfan intense fluid mixing was observed at the level of the pycnocline. This work was carried out in the frames of the Project INTAS-01-0025.