## Abstract

Scale analysis indicates that five nondimensional parameters (R_{0} ^{2}, ε, μ, λ and kλ) characterize the disturbance generated by the steady flow of a uniform wind (U_{0}, V_{0}) incident on a mountain ridge of width a. Here μ = h_{0}/H_{R} is the ratio of the mountain height h_{0} to the deformation depth H_{R} = fa/N where f is the Coriolis parameter and N is the static buoyancy frequency. The parameters λ = H_{R}/H and kλ are the ratios of H_{R} to the density scale height H and the potential temperature scale height H/k respectively. There are two Rossby numbers; ε = V_{0}/fa, and R_{0} = U_{0}/fa. If R_{0} ^{2} ≤ 1, then the mountain-parallel flow is in approximate geostrophic balance and the flow is semigeostrophic. If the flow is anelastic (λ ≃ 1), no direct correspondence between the two approximations was found. However the anelastic effects are qualitatively similar for the two and lead to: i) an increase in the strength of the mountain anticyclone, ii) a reduction in the extent (and possible elimination) of the zone of blocked, cyclonic flow, iii) a permanent turning of the flow proportional to the mass of air displaced by the mountain, and iv) an increase in the ageostrophic cross-mountain flow. The last result implies an earlier breakdown of semigeostrophic theory for anelastic flow over topography. Apart from a strengthening of the cold potential temperature anomaly over the mountain, the presence of a finite potential temperature scale height (ie k nonzero) does not significantly alter the flow solution. -from Authors

Original language | English (US) |
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Pages (from-to) | 1020-1029 |

Number of pages | 10 |

Journal | Journal of the Atmospheric Sciences |

Volume | 45 |

Issue number | 6 |

DOIs | |

State | Published - 1988 |

## All Science Journal Classification (ASJC) codes

- Atmospheric Science