Sierra Nevada mountain waves and rotors

Fifty years after the Sierra Wave Project, and nearly thirty years after the Colorado Lee Wave program, the atmospheric science community is revisiting the problem of large-amplitude mountain waves, rotors, and associated clear-air turbulence with a coordinated, two-phase field program and research effort (Sierra Rotors, 2004, and Terrain-induced Rotor Experiment, 2006). The goal of this effort is to improve the understanding and predictability of the coupled mountain-wave/rotor/boundary-layer system and the associated clear-air turbulence in complex terrain while taking advantage of the newest advances in remote sensing and mesoscale numerical modeling. Atmospheric rotors, intense low-level horizontal vortices that form along an axis parallel to and downstream of a mountain ridge crest, are know to pose a great hazard to aviation.

The Sierra Rotors project examined mountain waves and wave induced rotors in the lee of the Sierra Nevada in Owens Valley of eastern California during the spring of 2004. A range of instrumentation was deployed in Owens Valley, including a dense array of surface stations from DRI, two ISS (Integrated Sounding Systems) from NCAR, an MGLASS (radiosonde station) near Fresno, and various instruments and modeling efforts from other groups. Several strong wave events with rotors and attendant severe downslope windstorms were observed. This poster will present our current understanding of the Sierra Nevada mountain wave and rotor dynamics, based in part on the Sierra Rotors observations and real-data high-resolution numerical simulations.