Post by syzygy on Feb 22, 2018 7:21:55 GMT
Urban Heat Islands Punch Holes in Fog
download large image (6 MB, JPEG, 6187x6743) / acquired January 30, 2014
In 2016, a satellite image showed peculiar holes in a layer of fog over northern India. Those holes seemed to correspond with the locations of major cities, but the cause was a mystery.
“I would definitely say there is a connection with the cities,” said Steve Lang, a research meteorologist at NASA’s Goddard Space Flight Center in an Earth Observatory story about the phenomenon. “But without being there, we can only speculate that it could be due to either additional aerosols, urban heat islands, or both, having an effect on the clouds.”
A recent study led by Ritesh Gautam of the Indian Institute of Technology (now at Environmental Defense Fund), has found that Lang and other scientists were correct in their hypothesis that aerosols and urban heating can influence fog. The paper was published January 2018 in Geophysical Research Letters.
“The urban heat island effect is totally opposite to the effect that aerosols have on fog,” said Gautam. “On the one hand, you have air pollution likely amplifying fog. On the other, urban heating is helping fog dissipate faster.” The result is the formation of so-called “fog holes” that are occasionally visible over cities in satellite imagery.
Aerosol particles from pollution can serve as “seeds” that make it easier for fog to form. At the same time, an opposing effect can take place. Fog formation requires a stable layer of moist air—high relative humidity—in the lowest part of the atmosphere near the ground. But warm urban areas can reduce the relative humidity, making less moisture available for fog formation and leading to fog holes.
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download large image (2 MB, JPEG, 3912x2608) / acquired January 3, 2018
“In densely populated and polluted environments like India, the winter fog is a major environmental issue,” Gautam said. He notes that every December and January, dense fog disrupts transportation on a daily basis, causing massive delays and cancellations in air and rail travel, and leading to numerous car accidents. Air quality and public health issues are also a concern.
“There has been a long-standing need in India to develop sophisticated fog prediction capability to aid air and rail transportation management,” Gautam said. “Fog holes add another important dimension to the fog problem, where we must account for the urban heating effect when assessing the interactions between aerosols and fog.”
India is not the only place where the effect has been observed. Gautam’s team found fog holes over China, Europe, and the United States.
download large image (6 MB, JPEG, 6187x6743) / acquired January 30, 2014
In 2016, a satellite image showed peculiar holes in a layer of fog over northern India. Those holes seemed to correspond with the locations of major cities, but the cause was a mystery.
“I would definitely say there is a connection with the cities,” said Steve Lang, a research meteorologist at NASA’s Goddard Space Flight Center in an Earth Observatory story about the phenomenon. “But without being there, we can only speculate that it could be due to either additional aerosols, urban heat islands, or both, having an effect on the clouds.”
A recent study led by Ritesh Gautam of the Indian Institute of Technology (now at Environmental Defense Fund), has found that Lang and other scientists were correct in their hypothesis that aerosols and urban heating can influence fog. The paper was published January 2018 in Geophysical Research Letters.
“The urban heat island effect is totally opposite to the effect that aerosols have on fog,” said Gautam. “On the one hand, you have air pollution likely amplifying fog. On the other, urban heating is helping fog dissipate faster.” The result is the formation of so-called “fog holes” that are occasionally visible over cities in satellite imagery.
Aerosol particles from pollution can serve as “seeds” that make it easier for fog to form. At the same time, an opposing effect can take place. Fog formation requires a stable layer of moist air—high relative humidity—in the lowest part of the atmosphere near the ground. But warm urban areas can reduce the relative humidity, making less moisture available for fog formation and leading to fog holes.
...
download large image (2 MB, JPEG, 3912x2608) / acquired January 3, 2018
“In densely populated and polluted environments like India, the winter fog is a major environmental issue,” Gautam said. He notes that every December and January, dense fog disrupts transportation on a daily basis, causing massive delays and cancellations in air and rail travel, and leading to numerous car accidents. Air quality and public health issues are also a concern.
“There has been a long-standing need in India to develop sophisticated fog prediction capability to aid air and rail transportation management,” Gautam said. “Fog holes add another important dimension to the fog problem, where we must account for the urban heating effect when assessing the interactions between aerosols and fog.”
India is not the only place where the effect has been observed. Gautam’s team found fog holes over China, Europe, and the United States.
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(thought, no placemark needed, also been lazy to throw an overlay, still have found interesting enough to share)
