Why tornadoes take weekends off

Scientists have released a new study revealing human activity may be the culprit behind an increase in tornadoes and hailstorms during summer weekdays. It turns out severe weather is higher during the week due to reduced air quality. Simply put, it's linked to our commute.

A research team analyzed summertime storm activity in the eastern U.S. from 1995 to 2009 using data from the National Oceanic and Atmospheric Administration's (NOAA) Storm Prediction Center. The data revealed tornadoes and hailstorms occurred at a rate of 20 percent above average during the week, and 20 percent below on the weekend.

The findings proved to not be random, and in fact, matched with similar cycles seen in other storms.

The researchers also looked at EPA air quality data. They noticed human-made summertime air pollution over the east coast spikes midweek, just like severe weather. This led the researchers to make the link to the pollution we create while driving to and from work.

Why would pollution have anything to do with tornadoes and severe weather? Explaining the hail is easy. Moisture gathers around specks of pollutants; this in turn leads to more cloud droplets as the pollution increases. Computer models indicate as these heavy droplets get picked up higher into the air they can cause more hail.

So now for the tornadoes. How does that work? It seems the larger, heavier hail producing droplets created by pollutants have less surface area than an equal mass of smaller particles of normally condensed water droplets or ice. The pollutant based droplets evaporates more slowly and are not as likely to pull heat from the air. This makes it easier for the warm air to help form supercells that spawn tornadoes.

The western U.S. gets a break because the air is too dry and the cloud masses too high and too cold for pollution to react in the same way.

So while reducing pollution is something we should be doing anyway the overall quality of the planet and our health, we've now got another reason to add to the pile. It may just be the reason we've all been needing to start needling our bosses about more telecommuting time.

The research team of Daniel Rosenfeld and colleague Thomas Bell detailed their findings in the October issue of the Journal of Geophysical Research-Atmospheres.

National Geographic, via Ecogeek

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