In situ measurements of 3D turbulence in Hurricanes Frances and Ivan using a pressure-sphere anemometer

As part of a joint effort between NOAA and the CBLAST Hurricane program, the NOAA Air Resources Laboratory has developed an Extreme Turbulence (ET) probe for measuring 3D turbulence and fluxes in hurricanes. This probe is a surface-based system that uses pressure-sphere anemometry, which is commonly employed for aircraft gust probes. It uses a 43 cm fiberglass sphere with 30 pressure ports distributed over its surface. Special modifications were developed to prevent water and spray from fouling the ports during a hurricane deployment. Turbulence data from the system are archived at 50 Hz.

In September 2004, a set of ET probes was successfully deployed into Hurricanes Frances and Ivan as they made landfall along the U.S. Coast. Three probes were deployed along the Atlantic Coast of Florida for Hurricane Frances. They were located to the north of the eye and collected data over approximately a 30 hour period during the landfall. Two probes were deployed near the coast at the Florida-Alabama border for Ivan. These probes operated for over 50 hours and passed near Ivan's eyewall.

Analysis of the data from the deployments indicates that the data are of high quality. Only rarely did the wind data show any evidence of the pressure ports being fouled by water. Velocity spectra computed from the ET measurements show the expected -5/3 inertial subrange, which is further evidence that the water fouling was minimal. In Ivan, the probes measured average pressures as low as 950 hPa and wind gusts up to about 50 m s^-1. A continuous 30 hour record of the turbulent kinetic energy (TKE) was generated from the Ivan data, showing that the TKE increased by a factor of ten as the storm came ashore. At its peak, the TKE was about 30 m² s^-2.