Excitation of spiral bands in hurricanes by interaction between the symmetric mean vortex and a shearing environmental steering current. Article

Willoughby, HE. (1979). Excitation of spiral bands in hurricanes by interaction between the symmetric mean vortex and a shearing environmental steering current. . JOURNAL OF THE ATMOSPHERIC SCIENCES, 36(7 , Jul. 1979), 1226-1235. 10.1175/1520-0469(1979)036<1226:eosbih>2.0.co;2

cited authors

  • Willoughby, HE

authors

abstract

  • In hurricanes, linear, stationary, asymmetric, inertia buoyancy oscillations can be resonantly forced at a radius where their tangential wavenumber times the orbital frequency of the mean swirling flow is equal to the local inertia frequency. If the hurricane is advected by an environmental geostrophic steering current without shear, the Coriolis force arising from the motion balances the environmental pressure gradient. However, if the motion of the storm differs from the geostrophic wind or if that wind has a horizontal shear, this balance is disrupted. For a uniform shear, resolution of the imbalance into radial and tangential components leads to a forcing that has a symmetric component and asymmetric components with tangential wavenumbers + or !1 and + or !2. The symmetric and wavenumber + or !1 components have exponential horizontal structure, but the + or !2 components have sinusoidal structure and are amplified by the wave action conservation mechanism of Willoughby. These waves resemble the spiral bands observed by research aircraft in Hurricane Anita of 1977 . As is generally found for resonant forcing, the amplitude of the oscillations is sensitive to the dissipation rate, but for values of this quantity appropriate to cumulus friction and an enviromental shear equal to 10% of the Coriolis parameter, the maximum horizontal velocity amplitude in the eye wall is several metres per second. (A)

publication date

  • January 1, 1979

published in

start page

  • 1226

end page

  • 1235

volume

  • 36

issue

  • 7 , Jul. 1979