title: Numerical simulations of internal wave generation by convection in water.
abstract: Water's density maximum at 4°C makes it well suited to study internal gravity wave excitation by convection: an increasing temperature profile is unstable to convection below 4°C, but stably stratified above 4°C. We present numerical simulations of a waterlike fluid near its density maximum in a two-dimensional domain. We successfully model the damping of waves in the simulations using linear theory, provided we do not take the weak damping limit typically used in the literature. To isolate the physical mechanism exciting internal waves, we use the spectral code dedalus to run several simplified model simulations of our more detailed simulation. We use data from the full simulation as source terms in two simplified models of internal-wave excitation by convection: bulk excitation by convective Reynolds stresses, and interface forcing via the mechanical oscillator effect. We find excellent agreement between the waves generated in the full simulation and the simplified simulation implementing the bulk excitation mechanism. The interface forcing simulations overexcite high-frequency waves because they assume the excitation is by the "impulsive" penetration of plumes, which spreads energy to high frequencies. However, we find that the real excitation is instead by the "sweeping" motion of plumes parallel to the interface. Our results imply that the bulk excitation mechanism is a very accurate heuristic for internal-wave generation by convection.
authors.affiliation: Department of Astrophysics and Theoretical Astrophysics Center, University of California, Berkeley, California 94720, USA.|Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Lecoanet
authors.affiliation: CNRS, Aix-Marseille Université, Ecole Centrale Marseille, IRPHE, Marseille 13013, France.|Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California 90095, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Le Bars
authors.affiliation: Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA.|Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Keaton J
authors.initials: KJ
authors.lastname: Burns
authors.affiliation: School of Mathematics & Statistics, University of Sydney, NSW 2006, Australia.
authors.forename: Geoffrey M
authors.initials: GM
authors.lastname: Vasil
authors.affiliation: Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA.|Laboratory for Atmospheric and Space Physics and Department of Astrophysical & Planetary Sciences, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Brown
authors.affiliation: Department of Astrophysics and Theoretical Astrophysics Center, University of California, Berkeley, California 94720, USA.
authors.forename: Eliot
authors.initials: E
authors.lastname: Quataert
authors.affiliation: Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106, USA.|Department of Physics, Farmingdale State College, Farmingdale, New York 11735, USA.|Department of Astrophysics, American Museum of Natural History, New York, New York 10024, USA.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Oishi