Theoretical investigation of nonhydrostatic effects on convectively forced flows: Propagating and evanescent gravity-wave modes

Jaemyeong Mango Seo, Jong Jin Baik, Hye-Yeong Chun

Research output: Contribution to journalArticle

Abstract

Nonhydrostatic effects on convectively forced mesoscale flows are theoretically investigated using a linearized, two-dimensional, steady-state, nonrotating, Boussinesq airflow system with prescribed convective forcing. The nondimensionalized airflow system contains the nonhydrostaticity factor β = U/Na, where U is the basic-state wind speed, N is the basic-state buoyancy frequency, and a is the half-width of the convective forcing. In an inviscid-limit system, the solution for vertical velocity is classified into the propagating mode (k ≤ β-1, where k is the nondimensional horizontal wavenumber) and the evanescent mode (k > β-1). As β increases, an alternating wavy pattern of updrafts and downdrafts appears downstream of the convective forcing with a nondimensional horizontal wavelength of 2πβ corresponding to the nondimensional critical horizontal wavenumber kc = β-1. The momentum flux analysis shows that the alternating updrafts and downdrafts are almost horizontally propagating gravity waves of the propagating mode whose k is slightly smaller than kc and that these gravity waves strengthen the momentum flux above the convective forcing. In a viscous system, the solution for vertical velocity has propagating and decaying components simultaneously that cannot be explicitly separated. Here, the propagating mode and two evanescent modes are defined by comparing the magnitudes of the nondimensional vertical wavenumber and decay rate. For large viscous coefficients, the k-range of the propagating mode becomes narrow and the alternating updrafts and downdrafts are dissipated. As β increases, the propagating mode, which strengthens the momentum flux above the convective forcing, is effectively dissipated even with a small viscous coefficient.

Original languageEnglish
Article number126604
JournalPhysics of Fluids
Volume30
Issue number12
DOIs
Publication statusPublished - 2018 Dec 1

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gravity waves
vertical air currents
momentum
coefficients
buoyancy
decay rates
wavelengths

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics

Cite this

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abstract = "Nonhydrostatic effects on convectively forced mesoscale flows are theoretically investigated using a linearized, two-dimensional, steady-state, nonrotating, Boussinesq airflow system with prescribed convective forcing. The nondimensionalized airflow system contains the nonhydrostaticity factor β = U/Na, where U is the basic-state wind speed, N is the basic-state buoyancy frequency, and a is the half-width of the convective forcing. In an inviscid-limit system, the solution for vertical velocity is classified into the propagating mode (k ≤ β-1, where k is the nondimensional horizontal wavenumber) and the evanescent mode (k > β-1). As β increases, an alternating wavy pattern of updrafts and downdrafts appears downstream of the convective forcing with a nondimensional horizontal wavelength of 2πβ corresponding to the nondimensional critical horizontal wavenumber kc = β-1. The momentum flux analysis shows that the alternating updrafts and downdrafts are almost horizontally propagating gravity waves of the propagating mode whose k is slightly smaller than kc and that these gravity waves strengthen the momentum flux above the convective forcing. In a viscous system, the solution for vertical velocity has propagating and decaying components simultaneously that cannot be explicitly separated. Here, the propagating mode and two evanescent modes are defined by comparing the magnitudes of the nondimensional vertical wavenumber and decay rate. For large viscous coefficients, the k-range of the propagating mode becomes narrow and the alternating updrafts and downdrafts are dissipated. As β increases, the propagating mode, which strengthens the momentum flux above the convective forcing, is effectively dissipated even with a small viscous coefficient.",
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Theoretical investigation of nonhydrostatic effects on convectively forced flows : Propagating and evanescent gravity-wave modes. / Seo, Jaemyeong Mango; Baik, Jong Jin; Chun, Hye-Yeong.

In: Physics of Fluids, Vol. 30, No. 12, 126604, 01.12.2018.

Research output: Contribution to journalArticle

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