The temperature component is pretty straightforward, and most news reports focus on it. The air pressure part is a little more complicated. It refers to the difference in air pressure between the western and eastern parts of the equatorial Pacific. Scientists use readings from Darwin, on the north-central coast of Australia, and from Tahiti, more than 5, miles to the east. But from time to time, air pressure conditions change over the equatorial Pacific, affecting the trade winds, which normally blow from east to west.
The winds act on the surface of the water, which is warmed by the sun, pushing it along. And in the eastern Pacific cold, deep water rises up to replace it. A huge mass of warm water in the ocean transfers a lot of heat high into the atmosphere through convection — warm, moist air rising from the sea surface and forming thunderstorms. The heat in turn affects atmospheric circulation, both in the north-south direction and east-west.
The location of all that convection is important. The changes in atmospheric circulation can result in changes in weather in various parts of the world, what meteorologists call teleconnections. Much of this is related to the position of the jet stream, the high altitude winds that sweep across the planet from west to east. That can bring rainier, cooler conditions to much of the Southern United States, and warmer conditions to parts of the North.
Normal conditions: In December top figure in column to the right , the sea surface temperatures and the winds were near normal, with warm water in the Western Pacific Ocean right column of images, red on the top panel of the December plot , and cool water, called the "cold tongue" in the Eastern Pacific Ocean right column of images, green on the top panel of the December plot.
The winds in the Western Pacific are very weak see the arrows pointing in the direction the wind is blowing towards , and the winds in the Eastern Pacific are blowing towards the west towards Indonesia. The bottom panel of the December plot shows anomalies, the way the sea surface temperature and wind differs from a normal December. In December , the warm water right column of images, red in the top panel of the December plot has spread from the western Pacific Ocean towards the east in the direction of South America , the "cold tongue" right column of images, green color in the top panel of the December plot has weakened, and the winds in the western Pacific, usually weak, are blowing strongly towards the east, pushing the warm water eastward.
The anomalies show clearly that the water in the center of Pacific Ocean is much warmer red than in a normal December. This name was used for the tendency of the phenomenon to arrive around Christmas. The bottom panel in the animations, labeled anomalies, shows temperature deviations from normal how much the sea surface temperature is different from the long term average.
The red color in the anomalies plot indicates that the temperature of the water is much warmer than is normal for that month, whereas blue color indicates that the water is much cooler than is normal. In the left hand panel of the graphic below, you see the sea surface temperature at the Equator in the Pacific Ocean Indonesia is towards the left, South America is towards the right.
Time is increasing downwards from at the top of the plot, to the present, at the bottom of the plot. NOTE: Click to see a larger version of this annotated graphic or a larger, realtime version of this graphic with the latest data. Sea surface temperatures left panel : The first thing to note is the blue "scallops" on the right of the plot, in the eastern Pacific. These indicate the cool water typically observed in the Eastern Pacific called the "cold tongue". Cold tongue temperatures vary seasonally, being warmest in the northern hemisphere springtime and coolest in the northern hemisphere fall.
The red color on the left is the warm pool of water typically observed in the western Pacific Ocean. The anomalies show how much the sea surface temperature is different from the usual value for each month.
Water temperatures significantly warmer than the norm are shown in red, and water temperatures cooler than the norm are shown in blue. Notice the very cool water blue , in the Eastern Pacific, in All other graphics provided by the TAO project office.
See YouTube video.
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