We all know about the current controversies associated with the ozone layer or the global warming phenomenon. Now, the NASA’s Earth Science Enterprise (ESE) is warning us that atmospheric changes or El Niño events can affect the Earth’s rotation.
"Changes in the atmosphere, specifically atmospheric pressure around the world, and the motions of the winds that may be related to such climate signals as El Niño are strong enough that their effect is observed in the Earth’s rotation signal," said David A. Salstein, an atmospheric scientist from Atmospheric and Environmental Research, Inc., of Lexington, Mass., who led a recent study.
From year to year, winds and air pressure patterns change, causing different forces to act on the solid Earth. During El Niño years, for example, the rotation of the Earth may slow ever so slightly because of stronger winds, increasing the length of a day by a fraction of a millisecond (thousandth of a second).
Please read the article for technical explanations, images and animations. Here is a synthesis in plain English.
"The key is that the sum of the angular momentum (push) of the solid Earth plus atmosphere system must stay constant unless an outside force (torque) is applied," Salstein said. "So if the atmosphere speeds up (stronger westerly winds) then the solid Earth must slow down (length-of-day increases). Also if more atmosphere moves to a lower latitude (further from the axis of rotation), and atmospheric pressure increases, it also gains angular momentum and the Earth would slow down as well."
Salstein looked at meteorological and astronomical measurements from different sources and found they were in good agreement as this diagram demonstrates.
According to NASA's ESE, "it shows that changes in climate signals can have global implications on Earth's overall rotation."
Source: NASA Goddard Space Flight Center, March 4, 2003
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