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| Titel |
Transformation and disintegration of strongly nonlinear internal waves by topography in stratified lakes |
| VerfasserIn |
V. I. Vlasenko, K. Hutter |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 20, no. 12 ; Nr. 20, no. 12, S.2087-2103 |
| Datensatznummer |
250014521
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| Publikation (Nr.) |
 copernicus.org/angeo-20-2087-2002.pdf |
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| Zusammenfassung |
For many lakes the
nonlinear transfer of energy from basin-scale internal waves to short-period
motions, such as solitary internal waves (SIW) and wave trains, their
successive interaction with lake boundaries, as well as over-turning and
breaking are important mechanisms for an enhanced mixing of the turbulent
benthic boundary layer. In the present paper, the evolution of plane SIWs in a
variable depth channel, typical of a lake of variable depth, is considered,
with the basis being the Reynolds equations. The vertical fluid stratification,
wave amplitudes and bottom parameters are taken close to those observed in Lake
Constance, a typical mountain lake. The problem is solved numerically. Three
different scenarios of a wave evolution over variable bottom topography are
examined. It is found that the basic parameter controlling the mechanism of
wave evolution is the ratio of the wave amplitude to the distance from the
metalimnion to the bottom d. At sites with a gentle
sloping bottom, where d is small, propagating (weak
or strong) internal waves adjust to the local ambient conditions and preserve
their form. No secondary waves or wave trains arise during wave propagation
from the deep part to the shallow water. If the amplitude of the propagating
waves is comparable with the distance between the metalimnion and the top of
the underwater obstacle ( d ~ 1), nonlinear
dispersion plays a key role. A wave approaching the bottom feature splits into
a sequence of secondary waves (solitary internal waves and an attached
oscillating wave tail). The energy of the SIWs above the underwater obstacle is
transmitted in parts from the first baroclinic mode, to the higher modes. Most
crucially, when the internal wave propagates from the deep part of a basin to
the shallow boundary, a breaking event can arise. The cumulative effects of the
nonlinearity lead to a steepening and overturning of the rear wave face over
the inclined bottom and to the formation of a turbulent jet propagating
upslope. Some time later, after the breaking event, a new stable stratification
is formed at the site of wave destruction. The breaking criterion of ISWs is
discussed.
Key words. Oceanography: general
(limnology; numerical modeling) – Oceanography: physical (internal and
inertial waves) |
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