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| Titel |
The dynamics of buoyant jets in a linearly stratified ambient cross-flow: Implications for the interaction between volcanic plumes and wind |
| VerfasserIn |
Guillaume Carazzo, Frédéric Girault, Thomas Aubry, Helene Bouquerel, Edouard Kaminski |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093985
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| Publikation (Nr.) |
 EGU/EGU2014-9242.pdf |
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| Zusammenfassung |
| Volcanic plumes produced by explosive eruptions commonly interact with atmospheric wind
causing plume bending and a reduction of its maximum rise height. It is well known that the
maximum height reached by a buoyant plume rising in a cross-flow with uniform velocity is
controlled by the plume buoyancy flux at the source, the strength of the initial environmental
density stratification, the wind velocity and the efficiency of turbulent entrainment. Although
numerous studies have been carried out to understand the effects of variations of
environmental and source conditions on the plume maximum height, turbulent
entrainment has not been taken into account with the same level of detailed analysis.
Here, we present new laboratory experiments aimed at better understanding the
contribution of the turbulent entrainment to determining the plume maximum height. The
experiments consist in injecting downward fresh water in a tank containing an aqueous
NaCl solution with linear density stratification. The jet source is towed at a constant
speed through the stationary fluid in order to produce a cross-flow. According to
the range of source and environmental conditions, the buoyant jet is distorted or
bent-over and its maximum rise height is reduced up to a factor of 2 when wind speed
is high. We quantify the efficiency of turbulent entrainment due to wind in our
experiments and we show that the dynamical regime strongly depends on the ratio of
the horizontal wind speed and the vertical plume velocity, and on the Richardson
number defined at the source. Our results provide a robust framework to characterize
the entrainment coefficient due to wind in a 1D model of turbulent jet rising in a
linearly stratified ambient cross-flow, and hence can be used for the assessment of
the impact of atmospheric winds on the dynamics of explosive volcanic plumes. |
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