Measuring sea spray changes in hurricanes via measurements of salt concentrations in rain using a salinity/conductivity sensor on a NOAA research aircraft

Sea spray above the ocean surface in hurricanes enhances the transfer of sensible heat to the atmospheric boundary layer. Sea spray becomes of greater significance as the intensity and thereby wind speed of the hurricane increases. A fuller knowledge of the distribution of sea spray over the ocean may help in understanding changes in intensity of the most dangerous hurricanes.

An instrument to measure the salt content of rain has been developed and installed on one of NOAA's P3 hurricane research aircraft. Preliminary calibration of the instrument has been undertaken in mini wind tunnel tests in the laboratory by spraying a fine mist of water containing salt concentrations in the 0 to 100 ppm range on the sensor. On the ground the sensor was also tested with solutions while in place on a pylon on the wing of the plane using simple spray bottles. Further high quality calibrations will be conducted in the University of Texas A&M wind tunnel facility.

An earlier version of the sensor was flown into Hurricane Paloma (2008) at an elevation of 4 km. Limited calibration testing of this sensor suggest the salt concentrations ranged from 0 to 10 ppm.

Rain samples collected at ground level from eleven land falling hurricanes ranged from 5 ppm to 50 ppm (Lawrence et al, 2006 Fall AGU abstract, session A33). Hurricane Katrina showed the highest concentration of salt at 50 ppm.

The use of the sensor is also of value in assessing flight safety because salt encrustation in the turbo prop engines of the P3 aircraft can severely decrease engine power and performance as has been noted in past research flights.