Sierra Rotors and the Terrain-induced Rotor Experiment (T-REX)

The Terrain-induced Rotor Experiment (T-REX) is an initiative to study mountain-wave induced rotors and low- as well as upper-level turbulence in airflow over complex terrain. Rotors, low-level horizontal vortices that form parallel to, and downstream of, the mountain crest can pose severe aeronautical hazards and have been cited as causing aircraft upsets and accidents of commercial, military and civilian aviation. T-REX has been planned as a two-phase effort, with the Sierra Rotors experiment constituting its first phase. The geographical focus area of T-REX is Owens Valley in the southern Sierra Nevada in California.

In this talk we will report on the organization, conduct, and preliminary findings of the Sierra Rotors experiment, the intensive observation program of Phase I of T-REX, to take place in March and April 2004. The core of the ground-observing network in the Sierra Rotors experiment consists of the DRI network of automatic weather stations in Owens Valley supplemented with the two NCAR 915 MHz wind profilers (MAPR and MISS) plus two upwind radiosonde locations (NCAR MGLASS and NAS Lemoore). Following the intense observation period in March and April 2004, Phase I of T-REX will continue with a longer-term monitoring program to (1) establish quantitative characteristics of the rotor behavior including the rotor type and location as well as the frequency distribution of the mountain-wave events, (2) evaluate the extent to which current operational mesoscale models can reliably forecast the occurrence of rotors.

The Sierra Rotors experiment and the attendant numerical and theoretical studies are setting the stage for Phase II of T-REX, whose hallmark is a major field experiment in March-April 2006 featuring enhanced ground-based systems and airborne observing platforms. This phase will explore the interaction of lee waves, rotors and related turbulence zones by probing the mesoscale airflow between surface and 20 km altitude. We will also describe present plans for future activities and a preliminary organizational structure of Phase II of T-REX.