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Not a Myth: The Amount of Rain Depends (Slightly) on the Phase of the Moon
Researchers have found that the moon's tidal forces affect rainfall on earth. [eurekalert.org] From the EurekAlert article:
When the moon is high in the sky, it creates bulges in the planet's atmosphere that creates imperceptible changes in the amount of rain that falls below.
New University of Washington research to be published in Geophysical Research Letters shows that the lunar forces affect the amount of rain - though very slightly.
However the effect is not very strong:
The change is only about 1 percent of the total rainfall variation, though, so not enough to affect other aspects of the weather or for people to notice the difference.
The mechanism is explained as follows:
When the moon is overhead, its gravity causes Earth's atmosphere to bulge toward it, so the pressure or weight of the atmosphere on that side of the planet goes up. Higher pressure increases the temperature of air parcels below. Since warmer air can hold more moisture, the same air parcels are now farther from their moisture capacity.
"It's like the container becomes larger at higher pressure," Kohyama said. The relative humidity affects rain, he said, because "lower humidity is less favorable for precipitation."
Additional coverage is found at IFLScience. [iflscience.com]
The actual paper [wiley.com] is Open Acess.
However it seems not to be the first result of that type. When searching for more coverage, I've come across an article of USA today [usatoday.com] which, if I interpret the URL correctly, is from October 2010 (unfortunately I couldn't find any explicit date of the article). There they write:
But an upcoming study in the journal Geophysical Research Letters finds the phases of the moon appear to have some slight influence both on rainfall patterns and river flow across the USA, confirming ancient folklore that suggested such connections.
Researchers, led by Randy Cerveny of Arizona State University, found that rain and snow tends to increase slightly a few days prior to a quarter moon, which is roughly halfway between the full and new moons. This was also true for stream flow, the amount of water that flows through a river gauge.
While the journal is the same, Randy Cerveny is not one of the authors of the paper mentioned above. After searching for the author's name on the journal, I guess the paper they refer to is this one [wiley.com] from November 2010.
