Moon Affects Rainfall, Says Study Based on NASA and Japanese Aerospace Data

It has long been known that the moon's positioning in the sky changes the tides, but new evidence proves that the moon also affects precipitation amounts. Published in Geophysical Research Letters, the study demonstrates that the forces from the lunar cycle affect the amount of moisture the air holds.

"As far as I know, this is the first study to convincingly connect the tidal force of the moon with rainfall," Tsubasa Kohyama, a corresponding author and University of Washington doctoral student in atmospheric sciences, said in an official statement.

When the moon is high in the sky, the gravitational pull is greater -- causing the ocean waters to protrude outward. This creates high tides. In actuality, the entire atmosphere of the Earth bulges toward the moon when it is at its highest point.

Kohyama first noticed that there was a small fluctuation in air pressure when he began studying atmospheric waves; he and co-author John (Michael) Wallace, a professor of atmospheric sciences at the University of Washington looked into the strange actuality for two years.

Scientists first recognized that the moon's location affects air pressure in 1847, and Wallace and Kohyama published a paper substantiating this fact by using a global grid of data. Now, this new study verifies that the shift the moon causes on air pressure in fact results in less rainfall.

When the gravitational pull of an overhead moon causes the atmosphere to swell towards it, the pressure in the atmosphere rises, which in turn causes precipitation levels to fall. A higher air pressure warms the temperature of the air and warmer air can hold on to more moisture, thus producing less rain.

"It's like the container becomes larger at higher pressure," Kohyama said in a release, explaining that lower humidity produces less precipitation.

Based on data amassed by NASA and the Japan Aerospace Exploration Agency's Tropical Rainfall Measuring Mission satellite from 1998 to 2012, Kohyama and Wallace noted that rainfall is higher when the moon is higher--but only by about 1 percent.  

The scientists will continue to study the phenomenon and further investigate how the moon's phases correlate with rainfall amounts and the frequency of storms.

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