TY - JOUR

T1 - The Matsuno-Gill model on the sphere

AU - Shamir, Ofer

AU - Garfinkel, Chaim I.

AU - Gerber, Edwin P.

AU - Paldor, Nathan

N1 - Publisher Copyright:
© The Author(s), 2023. Published by Cambridge University Press.

PY - 2023/6/5

Y1 - 2023/6/5

N2 - We extend the Matsuno-Gill model, originally developed on the equatorial -plane, to the surface of the sphere. While on the -plane the non-dimensional model contains a single parameter, the damping rate, on a sphere the model contains a second parameter, the rotation rate (Lamb number). By considering the different combinations of damping and rotation, we are able to characterize the solutions over the plane. We find that the -plane approximation is accurate only for fast rotation rates, where gravity waves traverse a fraction of the sphere's diameter in one rotation period. The particular solutions studied by Matsuno and Gill are accurate only for fast rotation and moderate damping rates, where the relaxation time is comparable to the time on which gravity waves traverse the sphere's diameter. Other regions of the parameter space can be described by different approximations, including radiative relaxation, geostrophic, weak temperature gradient and non-rotating approximations. The effect of the additional parameter introduced by the sphere is to alter the eigenmodes of the free system. Thus, unlike the solutions obtained by Matsuno and Gill, where the long-term response to a symmetric forcing consists solely of Kelvin and Rossby waves, the response on the sphere includes other waves as well, depending on the combination of and. The particular solutions studied by Matsuno and Gill apply to Earth's oceans, while the more general -plane solutions are only somewhat relevant to Earth's troposphere. In Earth's stratosphere, Venus and Titan, only the spherical solutions apply.

AB - We extend the Matsuno-Gill model, originally developed on the equatorial -plane, to the surface of the sphere. While on the -plane the non-dimensional model contains a single parameter, the damping rate, on a sphere the model contains a second parameter, the rotation rate (Lamb number). By considering the different combinations of damping and rotation, we are able to characterize the solutions over the plane. We find that the -plane approximation is accurate only for fast rotation rates, where gravity waves traverse a fraction of the sphere's diameter in one rotation period. The particular solutions studied by Matsuno and Gill are accurate only for fast rotation and moderate damping rates, where the relaxation time is comparable to the time on which gravity waves traverse the sphere's diameter. Other regions of the parameter space can be described by different approximations, including radiative relaxation, geostrophic, weak temperature gradient and non-rotating approximations. The effect of the additional parameter introduced by the sphere is to alter the eigenmodes of the free system. Thus, unlike the solutions obtained by Matsuno and Gill, where the long-term response to a symmetric forcing consists solely of Kelvin and Rossby waves, the response on the sphere includes other waves as well, depending on the combination of and. The particular solutions studied by Matsuno and Gill apply to Earth's oceans, while the more general -plane solutions are only somewhat relevant to Earth's troposphere. In Earth's stratosphere, Venus and Titan, only the spherical solutions apply.

KW - atmospheric flows

KW - rotating flows

KW - shallow water flows

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U2 - 10.1017/jfm.2023.369

DO - 10.1017/jfm.2023.369

M3 - Article

AN - SCOPUS:85162213159

SN - 0022-1120

VL - 964

JO - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

M1 - A32

ER -