Recalculated Radiating Instabilities Using the Correct Matching and Boundary Conditions

Jae-Yul Yun Physical Oceanography Division, Korea Ocean Research and Development Institute, Seoul, Korea

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James M. Price Minerals Management Service, U.S. Department of the Interior, Herndon, Virginia

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Lorenz Magaard Department of Oceanography, University of Hawaii, Honolulu, Hawaii

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Abstract

Yun et al. (hereafter YPM) have reported results of a study on the radiating instabilities of nonzonal shear flows as a possible source of the energetic internal temperature fluctuations observed in the regions away from the axis of the Kuroshio Extension current. Kamenkovich and Pedlosky, however, pointed out that a matching condition and a boundary condition are incorrect in YPM’s formulation. In this paper, the radiating instabilities of zonal and northeastward flows are recalculated using the correct matching and boundary conditions, and the radiational properties of the solutions are discussed.

The solutions of YPM and this study on the northeastward flow are almost the same at short wavelengths up to several 100 km, and their differences become slightly greater as the wavelengths become closer to 2000 km due to a modification by the beta effect. However, the same conclusion made in YPM still holds in this analysis. That is, a strong shear flow with a northward or southward component is more likely than a zonal flow to radiate instability energy toward the far field for a given flow condition representing the midlatitude western North Pacific and it does so with greater realism. This is due to the beta effect and the westward component of the crossflow radiation direction.

Corresponding author address: Dr. Jae-Yul Yun, Physical Oceanography Division, Korean Ocean Research and Development Institute, Ansan P.O. Box 29, 425-600 Seoul, Korea.

jyyun@kordi.re.kr

Abstract

Yun et al. (hereafter YPM) have reported results of a study on the radiating instabilities of nonzonal shear flows as a possible source of the energetic internal temperature fluctuations observed in the regions away from the axis of the Kuroshio Extension current. Kamenkovich and Pedlosky, however, pointed out that a matching condition and a boundary condition are incorrect in YPM’s formulation. In this paper, the radiating instabilities of zonal and northeastward flows are recalculated using the correct matching and boundary conditions, and the radiational properties of the solutions are discussed.

The solutions of YPM and this study on the northeastward flow are almost the same at short wavelengths up to several 100 km, and their differences become slightly greater as the wavelengths become closer to 2000 km due to a modification by the beta effect. However, the same conclusion made in YPM still holds in this analysis. That is, a strong shear flow with a northward or southward component is more likely than a zonal flow to radiate instability energy toward the far field for a given flow condition representing the midlatitude western North Pacific and it does so with greater realism. This is due to the beta effect and the westward component of the crossflow radiation direction.

Corresponding author address: Dr. Jae-Yul Yun, Physical Oceanography Division, Korean Ocean Research and Development Institute, Ansan P.O. Box 29, 425-600 Seoul, Korea.

jyyun@kordi.re.kr

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  • Kamenkovich, I. V., and J. Pedlosky, 1996a: Radiating instability of nonzonal ocean currents. J. Phys. Oceanogr.,26, 622–643.

  • ——, and ——, 1996b: On the correct matching and boundary conditions for a radiating broken-line current. J. Phys. Oceanogr.,26, 1664–1665.

  • McIntyre, M. E., and M. A. Weissman, 1978: On the radiating instabilities and resonant over-reflection. J. Atmos. Sci.,35, 1190– 1196.

  • Pedlosky, J., 1977: On the radiation of meso-scale energy in the mid-ocean. Deep-Sea Res.,24, 591–600.

  • Talley, L. D., 1983: Radiating barotropic instability. J. Phys. Oceanogr.,13, 972–987.

  • Yun, J.-Y., 1986: Baroclinic instabilities of nonzonal ocean currents with application to the Kuroshio Extension Current. Ph.D. dissertation, University of Hawaii, 147 pp.

  • ——, J. M. Price, and L. Magaard, 1995: Radiating instability of nonzonal oceanic shear flows with application to the Kuroshio Extension current. J. Phys. Oceanogr.,25, 1778–1804.

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