4.5A The Life Cycle of Mountain Waves Forced by a Midlatitude Cyclone Encountering an Isolated Ridge

Monday, 18 August 2014: 3:45 PM
Kon Tiki Ballroom (Catamaran Resort Hotel)
Maximo Q. Menchaca, University of Washington, Seattle, WA; and D. R. Durran

Idealized studies of mountain waves have primarily focused on the steady state response to horizontally uniform flows encountering an obstacle. In this research, we extend previous studies of non-steady mountain waves to examine their generation, propagation, and dissipation when forced by a midlatitude cyclone impinging on an isolated ridge. The cyclone is obtained by superimposing a localized finite amplitude potential vorticity on a baroclinically unstable jet. Localized terrain is placed in an initially quiescent region of the flow, away from the initial PV anomaly. The maturing cyclone propagates towards the terrain, generating gravity waves exhibiting strong time dependent behavior that are affected by the changing flow.

Significant wave genesis is tied to the passage of surface fronts and their accompanying jet streaks and stronger surface winds. Wave packets advect downstream after front passage, causing noticeable wave-mean flow interaction. Waves generated by cold fronts impinging on terrain are compared with waves generated by warm fronts, allowing for exploration into the influence of directional shear on waves. Mountain waves produced by warm fronts have shorter horizontal and vertical wavelength and do not propagate far from their source compared with mountain waves produced by cold fronts. These simulations also produce many other realistic features, including wave breaking and downslope windstorms.

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