P3.19
Mountain waves over the Hohe Tauern
James D. Doyle, NRL, Monterey, CA; and R. B. Smith
The structure and intensity of large-amplitude trapped lee waves over the Hohe Tauern range of the Alps on 20 September 1999 during MAP IOP 2 are investigated through the analysis of in situ aircraft observations, airborne lidar, GPS dropsondes, rapid-scan satellite imagery, and a suite of linear and nonlinear model simulations. Observations indicate that the lee waves attained a maximum vertical velocity of more than 9 m/s, potential temperature perturbations greater than 10 K, and a horizontal wavelength of approximately 12-15 km. High-resolution nonlinear simulations accurately capture the trapped wave evolution and characteristics. Blocking of the southerly flow upstream of the Hohe Tauern decreases the depth of the layer that ascends the mountain crest and modulates the wave response. Vertically propagating waves are partially ducted into a train of lee waves as a result of a weak stability aloft, which forms due to diabatic processes associated with precipitation upstream of the Hohe Tauern crest. Linear analytic solutions confirm the importance of the weak stability layer in the upper-troposphere for the development of the nonhydrostatic evanescent waves. Results from idealized two-dimensional nonlinear simulations suggest that the vertical depth of diabatic heating associated with the upstream precipitation is important. When the latent heating depth is relatively shallow, gravity wave amplification and high drag occur beneath a diabatically-induced wave duct that is consistent with nonlinear resonance theory for the severe windstorm state.
Poster Session 3, Topographic Flows (with Coffee Break)
Thursday, 20 June 2002, 2:45 PM-4:30 PM
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