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Barotropic to baroclinic energy conversion using a time-varying background density

Published online by Cambridge University Press:  11 May 2021

Sorush Omidvar Open the ORCID record for Sorush Omidvar [Opens in a new window] ,
Mohammadreza Davoodi Open the ORCID record for Mohammadreza Davoodi [Opens in a new window]  and
C. Brock Woodson Open the ORCID record for C. Brock Woodson [Opens in a new window]
Sorush Omidvar*
Affiliation:
School of Environmental, Civil, Agricultural, and Mechanical Engineering, University of Georgia, Athens, GA30602, USA
Mohammadreza Davoodi
Affiliation:
UT Arlington Research Institute, University of Texas at Arlington, Fort Worth, TX76118, USA
C. Brock Woodson
Affiliation:
School of Environmental, Civil, Agricultural, and Mechanical Engineering, University of Georgia, Athens, GA30602, USA
*
†Email address for correspondence: sorush.omidvar@gmail.com
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Abstract

Internal wave generation is fundamentally the conversion of barotropic to baroclinic energy that often occurs due to vertical acceleration of stratified flows over topographic features. Acceleration results in a phase lag between density (pressure) perturbations and the barotropic velocity. To estimate the conversion of barotropic to baroclinic energy, the density perturbation is often calculated using a time-invariant background density. Other phenomena, however, can also alter the phasing of density perturbations and vertical velocities, such as barotropic tidal heaving and internal wave interactions. Consequently, accurately accounting for these dynamics in energy budgets is important. Tidal averaging or modal decomposition are often used to isolate topographic energy conversion in the presence of these other phenomena. However, while effective, these methods do not provide insights into the dynamics of conversion either through time or over depth. Here, we present a new analytical approach to calculating barotropic to baroclinic conversion using a time-varying background density. Our method results in an additional term in the baroclinic energy budget that directly accounts for barotropic tidal heaving and internal wave interactions, depending on the formulation of the background density. The tidally averaged, domain-integrated conversion rate is consistent across methods. Isolation of topographic conversion demonstrates that conversion due to interactions between internal wave beams and barotropic tidal heaving lead to relatively small differences in the overall conversion. However, using a time-varying background density allows for full decomposition of barotropic to baroclinic conversion through time and the identification of regions where negative conversion related to mixing actually occurs.

JFM classification

Geophysical and Geological Flows: Coastal engineering Geophysical and Geological Flows: Internal waves Geophysical and Geological Flows: Ocean processes
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 918 , 10 July 2021 , A26
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Copyright
© The Author(s), 2021. Published by Cambridge University Press

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