Phases of the Moon has a slight effect on rainfallAmy Walsh (Author) Published Date : Feb 01, 2016 13:27 IST
Phases of moon has an effect on the amount of rainfall. Researchers from University of Washington have stated that 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.
The research will be published in Geophysical Research Letters. It shows that the lunar forces affect the amount of rain, however the effect is not much.
Before this study, Peter Thorne, a climate scientist at National Climatic Data Center in North Carolina, had stated that it's not a strong link. The lunar variations seem to account for 1% to 2% of the total changes in rainfall or stream runoff. It's a real effect, but it's a real small effect, Thorne says.
The researchers still aren't sure how the moon exerts this effect. Most guesses also come from the 1960s and '70s. Back then, some scientists suggested that the moon's orbit could distort the magnetosphere, a region of ionized particles surrounding Earth's protective magnetic field. This might allow more particles from space into the atmosphere, where they could trigger rain when they collide with clouds.
As far as I know, this is the first study to convincingly connect the tidal force of the moon with rainfall, said corresponding author Tsubasa Kohyama, a UW doctoral student in atmospheric sciences.
Kohyama was studying atmospheric waves when he noticed a slight oscillation in the air pressure. He and co-author John (Michael) Wallace, a UW professor of atmospheric sciences, spent two years tracking down the phenomenon.
Air pressure changes linked to the phases of the moon were first detected in 1847,and temperature in 1932, in ground-based observations. An earlier paper by the UW researchers used a global grid of data to confirm that air pressure on the surface definitely varies with the phases of the moon.
When the moon is overhead or underfoot, the air pressure is higher, Kohyama said.
Their new paper is the first to show that the moon's gravitational tug also puts a slight damper on the rain.
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.
Kohyama and Wallace used 15 years of data collected by NASA and the Japan Aerospace Exploration Agency's Tropical Rainfall Measuring Mission satellite from 1998 to 2012 to show that the rain is indeed slightly lighter when the moon is high. 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.
Wallace plans to continue exploring the topic to see whether certain categories of rain, like heavy downpours, are more susceptible to the phases of the moon, and whether the frequency of rainstorms shows any lunar connection.
Phases of the Moon has a slight effect on rainfall