Click on the image above to view regional images.
Satellite derived wind speeds are obtained by both passive (radiometer) and active (scatterometer) means. Both rely on measuring the scattering effect produced when microwaves are reflected off the ocean surface. A rough ocean surface returns a stronger signal because the waves reflect more energy back to the sensor while a smooth ocean surface returns a weaker signal. The version 0.3 Experimental Doldrums product is derived using the NOAA NESDIS National Climatic Data Center Blended Sea Winds product. The blended product offers globally 0.25°x0.25° ocean surface (10-meter height) winds interpolated from multiple (up to six) satellite observations. The blending of multiple satellite observations allows for greatly enhanced temporal resolution (up to 6 hourly). These data are freely available from NCDC along with complete documentation.
The 6 hourly near real-time Blended Sea Winds are produced quasi-daily and available from NCDC. The blended product is a composite of up to six satellite observations. Currently these include SSMI F13, SSMI F14, TMI, QuikSCAT, SSMI F15, and AMSR-E. NOAA Coral Reef Watch then uses these data to identify regions of low wind conditions defined here as exhibiting a daily mean of less than 3 m/s (i.e. "doldrums"). The duration of these doldrums events is then tracked by accumulating the number of days over which this condition is met (doldrums days). As an experimental product it undergoes continual development and refinement 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).
Note: This Doldrums product is based on a version of near-real-time (NRT) (about a 24-hour delay) Blended Sea Winds produced quasi-daily. Since the updates are done automatically under a non-operational environment (no 24/7 IT support), timely production is not guaranteed.
Update Oct 6, 2011: Since Oct 4, 2011, the Blended Sea Winds production has been impacted because of the loss of data from the AMSR-E instrument. Input data from two additional satellites (SSMI F15 ver.6 and F17 ver.7) are now added to the experimental near-real-time Blended Sea Winds. Users should exercise caution until the characteristics of the modified Seawinds product have been established. See Aqua/AMSR-E press release for details.
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, explicit 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.
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.
Manzello D, Hendee JC, Ward D, Hillis-Starr Z. (2006) An
Evaluation of Environmental Parameters Coincident with the
Partial Bleaching Event in St. Croix, U.S. Virgin Islands 2003.
Proceedings of the 10th International Coral Reef Symposium,
Okinawa, Japan, 709-717
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.
Manzello D, Hendee JC, Ward D, Hillis-Starr Z. (2006) An Evaluation of Environmental Parameters Coincident with the Partial Bleaching Event in St. Croix, U.S. Virgin Islands 2003. Proceedings of the 10th International Coral Reef Symposium, Okinawa, Japan, 709-717Mumby P. J., Skirving W., Strong A. E., Hardy J. T., LeDrew E. F., Hochberg E. J., Stumpf R. P., and David L. T. (2004) Remote sensing of coral reefs and their physical environment. Marine Pollution Bulletin 48(3-4), 219.
Obura D. O. (2005) Resilience and climate change: lessons from coral reefs and bleaching in the Western Indian Ocean. Estuarine, Coastal and Shelf Science 63(3), 353.
Perry, K.L. et al, 2001. SeaWinds on QuikSCAT Level 3 Daily, Gridded Ocean Wind Vectors(JPL SeaWinds Project), Version 1.1, JPL Document D-20335, Jet Propulsion Laboratory, Pasadena, CA.
Skirving WJ, Guinotte J. (2001) The sea surface temperature story on the Great Barrier Reef during the coral bleaching event of 1998. In: Wolanski E(ed) Oceanographic process of coral reefs: physical and biological links in the Great Barrier Reef. CRC Press, Boca Raton
Zhang, H.-M., J.J. Bates, and R.W. Reynolds. (2006) Assessment of composite global sampling: Sea surface wind speed. Geophysical Research Letters VOL. 33, L17714, doi:10.1029/2006GL027086.
Zhang, H.-M., R.W. Reynolds, and J.J. Bates. (2006) Blended and Gridded High Resolution Global Sea Surface Wind Speed and Climatology from Multiple Satellites: 1987 - Present. American Meteorological Society 2006 Annual Meeting, Paper #P2.23, Atlanta, GA, January 29 - February 2, 2006.