Self-consistency of turbulence spectra measured with the helicopter-borne turbulence measurement system HELIPOD during PHELIX

HELIPOD is one of the most advanced airborne turbulence measurement systems that are currently available to the atmospheric sciences community. HELIPOD has a mass of 250 kg, is 5 m long, is suspended about 15 m below a helicopter, and is operated at a forward velocity of typically 40 m/s, so that the downwash of the helicopter does not contaminate the turbulence measurements. HELIPOD's output includes 100-Hz data streams of three-dimensional wind velocity, humidity, temperature, and static pressure. The system has been operated at altitudes as low as 8 m AGL, as well as up to 2 km AGL. HELIPOD was operated in November 1997 during the three-week long Profiler-HELIPOD Intercomparison Experiment (PHELIX) at Vandenberg AFB at the Pacific coast near Santa Maria, CA.

In this contribution, turbulence spectra and vertical profiles of energy dissipation rates and structure parameters measured with HELIPOD during PHELIX in the California marine boundary layer and in the free atmosphere above the capping inversion are presented. Power spectra and cross spectra of temperature, humidity, and the three wind velocity components are compared against predictions from turbulence theory. Instrumental artifacts are identified, and their magnitude is discussed.