Why tornadoes take weekends?

Sweltering summer tornado and hail comply weekend Joneses. New research has opened up new ways of unintended impacts of human activities on the weather conditions.

Scientists analyzed the summer thunderstorms in the eastern U.S. from 1995 to 2009, using data Prediction Center storms the National Oceanic and Atmospheric Administration. It turned out that the mid-week frequency of tornadoes and hail, 20% higher than the average, and on weekends — falls 20% below the average.

The results are statistically significant, are not accidental and consistent observations of other types of storms.

The researchers analyzed data from air quality monitoring provodimogoUpravleniem by the U.S. Environmental Protection, and noticed that the summer of anthropogenic pollution in the eastern United States reached a peak in the middle of the week. It is understandable — gazuyut morning people at work, in the evening with her.

The authors believe that the two graphs have a connection. The fact that the moisture collected on the pollutant particles, and this effect contributes to the formation of clouds. Computer models suggest that such drops rise to colder layers, becoming more massive, and turn into hailstones.

Connection with a tornado is more complicated. Large hailstones, which were formed without the involvement of aerosols have a smaller surface area than the relatively small "hydrometeors" of the same weight, that is, particles of condensed water or ice. Hailstones evaporate more slowly, and therefore almost no suck heat from the air. This facilitates the formation of warm air sverhyacheek so-called, that is the type of clouds that usually bring tornadoes and hail.

Relationship between pollution and storms in the western U.S. is not looked through because the air is too dry and the cloud masses are too high, where there is too cold, says study co-author Daniel Rosenfeld of the Hebrew University (Israel).

According to him, such a connection — another good reason to fight air pollution.

Results of the study were published in Journal of Geophysical Research — Atmospheres.

Prepared according to the National Geographic.

Dmitry Tselikov

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