Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1997
Description:
A series of numerical experiments is conducted in order to examine the role of topographic
irregularities in generation of subinertial cross-channel barotropic currents and
to obtain quantitative estimates of the offshore flow amplitude, its ratio to the magnitude
of the alongshore currents and the alongshore correlation scale.
A periodic (along the coast) channel with geometry representative of continental
margins is considered. Topographic disturbances have multiple alongshore wavenumber
contributions, kT, and the amplitude proportional to kT-2 (except one experiment). The
motion is forced by spatially uniform and temporally varying alongshore wind stress,
which drives the background current along the channel. The background current adjusts
to topographic disturbances and, in particular, Barotropic Shelf Waves (BSW) result.
That gives rise to the offshore currents.
The amplitude of the cross-channel flow is shown to increase with kT in the long wave
limit (order of 100 km in the model) and, in contrast, to decrease with kT in the short
wave limit (less than 20 km in the model). As a rule, the strongest response is attained
on the intermediate scales where lee waves form most efficiently.
Hart's {1990} quasi-geostrophic solution provided quantitative parameters to explain
the scale dependence and helped to interpret the results of simulations meant to examine
sensitivity of the cross-channel flow characteristics to variation of the governing parameters.
It is shown that the structure of the resonant wave is established by the combination
of spatial properties of the bottom bumps, and by the period and amplitude of the fluctuating
background current. On the basis of this analysis, it is demonstrated how the
BSW dispersion diagram can be used for diagnostic purposes.
The averaged (in time and along the channel) amplitude of subinertial cross-channel
currents ranged from negligible values to about 5.5 cm/sec, indicating that, indeed,
rather substantial offshore flow can be generated due to the effect of the topographic
irregularities. The alongshore correlation scale was no smaller than about 5 km and in
a few simulations (for instance, with lee-wave-favourable mean wind included) reached
30 - 50 km.
Description:
This work was supported by the Office of Naval Research, Coastal Science Program,
Grant N00014-95-1-0580.
Keywords:
Upwelling
;
Waves
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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