The Environmental Fluid Dynamics Lecture Series Presents an IBM Lecture

1. Dr. Vanda Grubišić Director, Earth Observing Laboratory National Center for Atmospheric Research (NCAR) Thursday, September 5, 2013 3:00 p.m. 161 Fitzpatrick Hall The Environmental Fluid Dynamics Lecture Series Presents an IBM Lecture Wave-induced Boundary-layer Separation in the Lee of the Medicine Bow Mountains Two cases of mountain waves, rotors and the associated turbulence in the lee of the Medicine Bow Mountains in SE Wyoming have been investigated using aircraft observations and mesoscale numerical simulations. Analyzed measurements include observations from in situ sensors and high-resolution cloud radar on board the University of Wyoming King Air aircraft. The analyzed radar measurements comprise the first direct observations of the wave-induced boundary-layer separation. Physical interpretation of the documented phenomena in these two events was facilitated by mesoscale model simulations. The two events show some striking similarities but also significant differences. In both cases rotors were observed; but whereas one resembles a classical lee wave rotor, the other bears more resemblance to an atmospheric internal hydraulic jump, with mid-tropospheric gravity wave-breaking aloft. High-resolution dual-Doppler syntheses of the two-dimensional velocity fields in the vertical plane beneath the aircraft reveal the boundary-layer separation, the scale and structure of the attendant rotors, and downslope windstorms. In both cases, the rotor extended horizontally about 5-10 km and vertically 2-2.5 km. The characteristic strength of horizontal vorticitywithin the rotor zone was found to be 0.2 s-1. In one of the cases, several large sub-rotors of 500 m to 1000 m in diameter were identified inside the main rotor.