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Abstract
The characteristics of a series of cloud-delineated wake patterns downwind of isolated mountain barriers on the Alaskan Peninsula and eastern Aleutian Islands have been studied using a geometrically corrected NOAA satellite picture in conjunction with available meteorological information. Four of these wakes are shown to be atmospheric analogs of Kármán-type vortex streets observed in laboratory experiments. A critical Reynolds number of 92±5 has been estimated for the flow. The drag coefficients associated with the vortex streets varied from 1.1 for an irregular, asymmetrical wake to 2.3 for a regular, symmetrical wake; the turbulent eddy viscosity ranged from 1.2−1.8×103 m2 s−1 for the four vortex streets. The two vortex streets having the lowest Reynolds number flows (R= 97, 112) appear to have developed through a “double vortex street” laminar instability while the vortex street having the largest Reynolds number flow (R = 183) apparently developed through a “single vortex street” instability. Formation of the remaining vortex street (R= 120) appeared to result from a downstream growth of a mountain-induced instability in the wind field.
Abstract
The characteristics of a series of cloud-delineated wake patterns downwind of isolated mountain barriers on the Alaskan Peninsula and eastern Aleutian Islands have been studied using a geometrically corrected NOAA satellite picture in conjunction with available meteorological information. Four of these wakes are shown to be atmospheric analogs of Kármán-type vortex streets observed in laboratory experiments. A critical Reynolds number of 92±5 has been estimated for the flow. The drag coefficients associated with the vortex streets varied from 1.1 for an irregular, asymmetrical wake to 2.3 for a regular, symmetrical wake; the turbulent eddy viscosity ranged from 1.2−1.8×103 m2 s−1 for the four vortex streets. The two vortex streets having the lowest Reynolds number flows (R= 97, 112) appear to have developed through a “double vortex street” laminar instability while the vortex street having the largest Reynolds number flow (R = 183) apparently developed through a “single vortex street” instability. Formation of the remaining vortex street (R= 120) appeared to result from a downstream growth of a mountain-induced instability in the wind field.
