These global-scale, false-color images represent data collected bythe NOAA Advanced Very High Resolution Radiometer (AVHRR) sensor and compositedfor the months of April 1983 andApril 1989, respectively. Over the oceans, the colors represent seasurface temperature anomaly--reds show higher than average temperatures,blues are lower than average, and white is average. On land, the colorsrepresent anomalously high or low production of green foliage (alsoknown as vegetation index)--greens represent anomalously highproductivity and browns show areas of anomalously low productivity.These images demonstrate that there is a relationship between seasurface temperature and vegetation productivity.
Note that in April 1983, there was a large El Niño in the equatorialPacific Ocean, whereas the Southern Atlantic was cooler than average.Much of the continent of South America was experiencing drought or drierthan normal conditions, reflected by the low vegetation index values(brown pixels) at that time. Along the equator, winds tend to blow fromeast to west, helping transport moisture and rain clouds inland. Yet,because water evaporates much less readily from a cooler sea surfacethan from a warmer one, the trade winds brought very littleprecipitation from the Southern Atlantic to South America at this time.Conversely, at higher latitudes in both the Northern and SouthernHemispheres, winds tend to blow from west to east. Notice the effects ofthe anomalously warm sea surface on both North America and Australiaduring this month. The large pocket of warm water off the west coast ofNorth America contributed to unusually high rainfall over the aridregions of Southern California and New Mexico, helping to spawntemporary grasslands where there is typically desert. Notice also howthe large region of anomalously warm water in the Indian Oceancontributed to extensive greening across the typically dry Australianoutback.
In contrast, April 1989 was a La Niña year in the equatorial Pacificand the Southern Atlantic was warmer than average. Many of the signalsdescribed in the previous paragraph appear to be reversed in this laterimage. For instance, the warm Atlantic waters are feeding more moisturethan usual into the overlying atmosphere, which was eventuallyprecipitated across South America, hence the greener than averagelandscape. However, the large pocket of cool water off the west coastof North America contributed to drought in the Great Plains region.There was also extensive drying across northern Australia as much of theIndian Ocean was cooler than normal.
For more information and animations, see NASADemonstrates How Earth's Global Heat Engine Drives Plant Growth
References & Resources
Images by Marit Jentoft-Nilsen; data courtesy Sietse Los, James Collatz, & Jim Tucker, NASA's Goddard Space Flight Center
