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Tiny particles = bigger storms
A Hebrew University of Jerusalem study shows that mankind has likely altered rainfall and weather.
Man-made pollution consisting of even the tiniest particles may have greater impact on weather systems and crops than previously thought, according to research done at Hebrew University of Jerusalem that has just been published in the prestigious journal Science.

Scientists, including second author Prof. Daniel Rosenfeld of HU’s Institute of Earth Sciences, studied the role of ultrafine particles on thunderstorms. While larger particles are known to enhance thunderstorms, scientists had not observed – until now – that even smaller particles, like those produced by vehicles and industry, could have the same effect. Furthermore, this new study reveals that the ultra-fine particles could invigorate rain clouds and increase rainfall in a much more powerful way than their larger counterparts.

The study focuses on the power of manmade emissions to trigger rain clouds and intensify storms. These aerosols come from urban and industrial air pollution, wildfires and other sources. While scientists have known that these particles play an important role in shaping weather and climate, the new study shows that even the smallest of man-made particles can have an outsize effect, creating more severe thunderstorms that in turn may lead to soil erosion, runoff and crop damage.

These tiny pollutants – less than one-thousandth the width of a human hair – were long thought to be too small to have much impact on raindrop formation. However, according to lead-author Dr. Jiwen Fan of the US Department of Energy’s Pacific Northwest National Laboratory, “We showed that the presence of these particles is one reason why some storms become so strong and produce so much rain. In a warm and humid area where atmospheric conditions are otherwise very clean, the intrusion of very small particles can make quite an impact.”

The study was conducted in the Amazon, a largely pristine, untouched area in South America. This setting gave scientists the rare opportunity to study the impact of pollution from nearby Manaus, a city of two million people in the region, and to pinpoint the effects of human pollution on a heretofore pristine weather environment.

“This groundbreaking research strongly suggests that mankind has likely altered the rainfall and weather in densely populated tropical- and summer-monsoon areas such as India, Southeast Asia, Indonesia, and even southeastern US,” said Rosenfeld, who has done much research in the field of particles and rain. Significantly, this heavier downpour often leads to soil erosion and crop damage, affecting the lives and livelihoods of those living in the affected areas.

Through detailed computer simulations, the scientists showed how the smaller particles have a powerful impact on rain clouds. While small in size, these particles are large in number and serve as a platform upon which small water droplets congregate and excess water vapor condenses. This enhanced condensation releases more heat, which in turn cause updrafts to become more powerful. The updrafts cause more warm air to be pulled into the clouds, which ultimately produces more ice and snow pellets, lightning, and heavier rain in the regions.
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