When Weather Follows the Workweek

Ever get the feeling that bad weather tends to form oh so "conveniently" around your commute to work? Studies linking air pollution to weather phenomena indicate that for some regions in the U.S., this trend may not be all in your head.

The reports have identified weekly cycles in weather phenomena, including rainfall, lightning, and storms. These cycles describe what is called the weekend effect, a trend in which these phenomena occur more frequently on the five day work week of warmer months than on weekends due to air pollution and emissions. To add to the list, a new study published by the Journal of Geophysical Research says tornadoes and hail storms follow similar patterns.

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The Science

The link between these cycles and air pollution is explained by heat transfer and changes in temperature. Aerosol particles from pollutants are a type of condensation nuclei, meaning more cloud droplets form with higher levels of pollution. Since the moisture in the cloud is spread among more particles, the droplet size is also smaller. Smaller size means rain develops higher in the cloud. This height has a direct impact on the severity of weather conditions.

To begin, condensation at higher heights provides more potential for clouds to develop into storms. Droplets which reach greater heights will also form larger rain droplets, and can even form hail if carried above the freezing line. Large droplets can encourage the formation of tornadoes because they provide less evaporative cooling during descent, while hail stones can stimulate the formation of lightning.

The Study

The new study of these patterns for hail and tornadoes was carried out using statistics and carefully selected data to ensure its accuracy. Long term trends and seasonal patterns were used to adjust the analyzed recordings, and only numbers from 1995 and above were used to prevent bias from advancements in weather-observing equipment.

The analysis was conducted separately for each month and region of the eastern U.S. It was found that correlation is significant and relevant only in the southeastern U.S. during the summer months. This is because warm, moist conditions are required for these effects to manifest.

What does this study mean? Is the U.S. government one step closer to controlling the weather through labor regulations? Do people in Florida have work schedules to blame for harsh storms? Perhaps not, but it does provide some insight into the effect of air pollution on the development of severe weather.

Source:

Ars Technica