During February 2014, National Weather Service/Ocean Prediction Center
) scientist Joe Sienkiewicz took part in the Ocean Winds Winter Experiment based out of Halifax, Nova Scotia. The goal of the experiment was to sample very high winds in ocean storms with the observing systems on the P-3 (Figure 1) and to synchronize the sampling with satellite overpasses. The satellites have instruments that can estimate the wind speed and direction near the ocean surface. Data collected are then used to improve the wind retrieval methods from the satellite scatterometers
. Joe helped plan three missions and adapt the flight plans underway to ensure the P-3 was positioned in the area of highest winds.
Figure 1. NOAA WP-3D N42R on a cold February morning in Nova Scotia waiting to head out into a storm over the North Atlantic.
Satellite derived ocean surface winds from radar instruments called scatterometers are used by forecasters at the Ocean Prediction Center (OPC), the National Hurricane Center (NHC), coastal Weather Forecast Offices and other national weather centers to monitor wind conditions, to raise or lower wind warnings, assess the accuracy of weather model analyses and forecasts, and verify forecasts. Scatterometer based winds help forecasters provide the most accurate information to help keep mariners safe.
Figure 2. Waves 25 to 30 feet in height as seen from the NOAA P-3 on Feb 14, 2014 south of Nova Scotia with winds to 65 knots (Hurricane Force).
The OPC, NHC and other warning centers across the globe warn for dangerous conditions at sea which are based on the Beaufort Wind Scale. Winter storms over the North Atlantic can be very intense with over forty storms this past winter season reaching hurricane force strength (Beaufort Force 12 - winds 72 MPH (64 knots) and greater). These storms move rapidly and often undergo explosive intensification with winds and waves becoming dangerous very quickly. That is why it is critical that winter ocean storms be sampled by the NOAA team on the P-3 and that satellite measurements be improved. Waves of 25 to 30 feet are shown south of Nova Scotia in Figure 2 from Feb 14, 2014. The highest winds were measured by the P-3 over the warm waters of the Gulf Stream.
Winds and waves are not the only hazard over the North Atlantic. February is cold and sea ice becomes a hazard over the Labrador Sea as shown in Figure 3. The prevailing winds were from the west and northwest and were forcing large areas of ice to break away from the main ice pack and drift into the open ocean. Figure 3 shows how the pack ice breaks up due to the wind forcing with large pieces breaking into smaller pieces and drifting away from the main pack.
Figure 3. Ice breaking away from the main pack over the Labrador Sea on 18 Feb 2014.
The P-3 can be used to validate other satellite measurements. After a flight over the Labrador Sea on Feb 18, sea ice was observed visually just off the eastern end of Nova Scotia in Cabot Strait. The sky was exceptionally clear and large areas of ice could be seen. The VIIRS imaging instrument on the Suomi NPP satellite passed over the same area within an hour of the P-3 and also observed the ice from space. The RADARSAT-2 Synthetic Aperture Radar followed a short while later and using its sophisticated, very high resolution radar was also able to sample the ice. All three images are in Figure 4. The view from the P-3 is highlighted by the red arrows in the VIIRS Visible image. Ice is the white mass in the photo from the P-3. To match the VIIRS and Radarsat-2 images the P-3 photo was inverted. The ice from VIIRS, Radarsat-2 (orange) and P-3 photo all match. Images from the NOAA NESDIS RADARSAT-2 winds product can be found at: http://www.ospo.noaa.gov/Products/ocean/sar/index.html.
Figure 4. Sea ice just east of Cape Breton, Nova Scotia as seen from the Suomi NPP satellite VIIRS imager (upper left), the NOAA P-3 (upper right), and the RADARSAT-2 Synthetic Aperture Radar (bright orange strands east of Nova Scotia)(lower).
The P-3 is an incredible resource and the information gathered has proven to be invaluable to gain trust in satellite remotely sensed ocean winds in high wind conditions and the basis to improve the estimation of the wind speeds.