NOAA’s airborne WSRA instrument provides forecasters with real-time ocean wave topography and other data while flying into hurricanes

Satellite image of Hurricane Lorenzo, Credit: NASA

Researchers from the Physical Sciences Laboratory (PSL) are lead authors of an article to appear in the Journal of Physical Oceanography, which provides an overview of NOAA’s Wide Swath Radar Altimeter (WSRA). Carried on a NOAA operational Hurricane Hunter P-3 aircraft, the WSRA is the only instrument that can produce a topographic map of the ocean waves. The WSRA operates unattended during hurricane flights, transforming the wave topography into directional wave spectra and reporting significant wave height, wavelength, and direction of the primary and secondary wave fields, rainfall rate and sea surface roughness. The data products are transmitted in real-time through a satellite data link to a ground station and then to the National Hurricane Center for use by forecasters in intensity projections and incorporation in hurricane wave models.

The WSRA was developed by ProSensing with funding from the NOAA Small Business Innovative Research and Joint Hurricane Testbed programs and additional support from the University of Massachusetts. PSL researcher Ed Walsh helped develop and refine the real-time processing capability and analyze the data products. PSL also funded system refinements and operational use for more than 10 years.

During the 2019 hurricane season, the WSRA flew aboard a NOAA P-3 aircraft into Hurricane Lorenzo when it was moving north about halfway between Florida and Africa. The WSRA documented a maximum wave height of 30 feet and captured the tremendous spatial variation of the wave field throughout all quadrants of Lorenzo. Specifically, the biggest waves were in the right front quadrant and nearly aligned with the local wind; the primary and the secondary wave fields were generally not aligned with the local wind in the left front quadrant; and in the center of the eye of the storm where there was no wind, the waves were 23 feet high and propagating towards the northwest. One key finding from this study was that the velocity of the waves in Hurricane Lorenzo was 2.4 times faster than it’s forward speed, indicating that wave generation weakens the storm by radiating the energy.

Waves generated by hurricanes represent a major threat to marine safety and coastal inundation. The environmental data collected by the WSRA can document the evolving characteristics of individual hurricanes, helping verify and improve the performance of ocean wave models. Including WSRA data in wave models could help improve predictions of hurricane track and intensity.

Walsh, Edward, Christopher Fairall, and Ivan PopStefanija (2021): In the eye of the storm, J. Phys. Oceanogr., (PSL Authors Bolded)