The NASA SeaWinds scatterometer onboard the QuikSCAT satellite has been providing continuous ocean surface wind data since July of 1999. The Ku-band scatterometer provides 25-km resolution wind fields for 90% of the Earth’s ocean surface every 24 hours. These data are freely available at the NASA-JPL Physical Oceanography Distributed Active Archive Center (PO.DAAC) at a variety of processing levels.

SeaWinds scatterometry uses a satellite microwave radar sensor to measure the backscatter effect produced when high radio frequency (RF) wave pulses scatter on the ocean surface. A rough ocean surface returns a stronger signal because the waves reflect more of the energy back to the scatterometer antenna while a smooth ocean surface returns a weaker signal. The NOAA NESDIS Marine Observing Systems Team applies an empirically derived model function to derive ocean surface (10 meter height) winds from the SeaWinds scatterometer and flags data that may be suspected rain contamination using the methods outlined in the NASA QuikSCAT Science Data Product User’s Manual.

Each day, QuikSCAT provides both an ascending pass (6AM LST equator crossing) and descending pass (6PM LST equator crossing). A composite of these twice daily passes are assembled on an approximately 0.25°x0.25° global grid. NOAA's CoastWatch, together with the Southwest Fisheries Science Center - Environmental Research Division, then compiles 4-day running means of these data and provides them to NOAA Coral Reef Watch via the Ocean Watch Live Access Server. NOAA Coral Reef Watch then uses these data to identify regions of low wind conditions defined here as exhibiting a 4-day mean of < 3 m/s and described as doldrums. The duration of these doldrums events is then tracked by accumulating the number of days over which this condition is met (doldrums days). This product is still undergoing development and analysis to determine the best configuration for the algorithm and to test its utility against past bleaching events.

While basin-scale coral bleaching occurs as a result of large-scale climate phenomena, local weather patterns greatly influence bleaching variability among sites within the basin. Three related factors that influence local bleaching patterns are temperature, light, and mixing. One parameter that exerts a common influence to all of these is wind, As wind speed falls there is reduced vertical mixing, evaporative cooling and sensible heat transfer increasing the likelihood of adverse temperature excursions during summer time maximum water temperatures (Mumby et al. 2001, Dunne and Brown 2001, Skirving and Guinotte 2001, Obura 2005). In addition, the pronounced stratification that can result under low-wind conditions can enhance the photo-degradation of colored dissolved organic material thereby reducing shading (Manzello et al., 2006).

The chart shown at the top of this page is a graphic display of regions exhibiting mean wind speeds of less than 3 m/s across multiple days for the period ending on the indicated date. The number of days at which this condition has persisted is denoted by the colorbar. Landmasses are mapped in grey; light grey regions depict non-valid pixels (e.g. landmask, ice) and white pixels are areas where insufficient data were retrieved throughout the latest four days to construct a composite (i.e. missing data).

Disclaimer: This is currently an experimental product and as such may contain inaccuracies. Neither Coral Reef Watch, NOAA, nor the United States Government, nor any of their employees or contractors, makes any warranty, express or implied, including warranties of merchantability and fitness for a particular purpose, or assumes any legal liability for the accuracy, completeness, or usefulness, of this information.

References

Dunne and Brown. (2001) The influence of solar radiation on bleaching of shallow water reef corals in the Andaman Sea, 1993-1998. Coral Reefs 20(3), 201.