Observational data sets and preliminary results are summarized for the Coupled Boundary Layer Air Sea Transfer (CBLAST) experiments flown into Hurricanes Fabian and Isabel (2003). The ONR/NOAA CBLAST 2003 experiment was flown in conjunction with the NOAA/NESDIS Ocean Winds experiment for deriving a high wind scatterometer algorithm for ocean surface wind speeds. CBLAST 2003 consisted of a series of 3 flight days, each consisting of two NOAA WP-3D research flights, which were flown into both Fabian and Isabel. In addition a pre-Fabian deployment of 16 drifting buoys and 6 subsurface oceanographic floats was conducted into the path of Fabian 24 hours prior to the second research flight by an Air Force Reserve WC-130J aircraft. It’s purpose was to obtain surface currents, ocean mixed layer observations and surface meteorological observations concurrent with subsequent research flights. These flights generated an unprecedented air-sea interaction data set for diagnosing surface fluxes at gale and hurricane force wind speeds and as input and ground truth for coupled air-sea numerical model predictions of hurricane intensity change.

The WP-3D flights consisted of two basic flight pattern modules. The first was the survey pattern designed to obtain sequences of 12 closely spaced GPS dropsonde segments across the eyewall in four quadrants of the storm. The objective, which was achieved, was to resolve eyewall boundary layer structure with sufficient detail to employ budget methods to diagnose momentum and enthalpy fluxes corresponding to maximum eyewall winds in excess of 60 m/s. A total of 300 eyewall sondes (350 overall) were deployed during the six flight days in CBLAST/ Ocean Winds in 2003.

The second CBLAST module was the stepped descent module designed to obtain turbulence and sea spray spectra at six different altitudes in the hurricane boundary layer for rain-free, gale force wind speeds- observations which would allow surface values to be deduced by extrapolation. The objective, achieved partially was to obtain along and cross wind stair-steps at two wind speed regimes in each of the three wave regimes around the storm defined by the Scanning Radar Altimeter (SRA). A total of 12 stepped descents were obtained in Fabian and Isabel.

Observations of 2-D wave spectra were obtained in Fabian with the SRA which showed the 3 distinctly different regimes of wave/swell interaction: 1) short, steep, growing waves moving with the wind in the rear and right-rear sectors, 2) large, mature waves in the right, right-front and front sectors moving right of the wind by 30-60 degrees and 3) large swell moving right of the wind by 60 to 120 degrees in the left-front, left and left-rear sectors.

Concurrent with the SRA measurements were observations of 1) turbulence from the Best Atmospheric Turbulence (BAT) Probe, IRGA and Licor fast response humidity systems, 2) spray droplet spectra from the CIP probe, 3) wave breaking from the Scripps high-speed, motion-compensated digital camera system, 4) continuous surface wind vector measurements from Stepped Frequency Microwave Radiometer (SFMR), UMASS C- and K-band scatterometers, which when operated synchronously make up the Integrated Wind and Rain Atmospheric Profiler (IWRAP), 5) continuous boundary layer wind profiles from both IWRAP and the P-3 Tail Doppler radar systems and 6) sea surface temperature (SST) in clear regions from a downward-looking, dual-frequency infrared radiometer. Taken together, these systems provided the observations needed for bulk estimates of surface fluxes from existing parameterizations as well as for creating new surface flux bulk parameterizations, a key goal of CBLAST.