Scientists from James Madison University have performed a multi-variable investigation of thunderstorm environments in two distinct geographic regions: the Washington, D.C. and Kansas City metropolitan regions.
Air pollution is increasing the severity of summertime thunderstorms. Image credit: ELG21.
Land cover and the properties of the atmospheric boundary layer modify thunderstorms and their signature phenomena — lightning.
Some of the sharpest contrasts in thunderstorms on the globe occur along the continental-ocean boundary.
In general, the land has an order-of-magnitude greater amount of lightning than the ocean.
Thermodynamic properties of the atmosphere change greatly because of differences in surface land cover.
“Pollution acts as cloud nuclei,” said James Madison University’s Professor Mace Bentley, lead author of the study.
“It gets brought into the cloud through the updraft; the updraft and downdraft then separate the pollution particles, which divides the electrical charges in the cloud and leads to more lightning production.”
For the study, the authors examined nearly 200,000 thunderstorms in the Washington, D.C., area and more than 300,000 in the Kansas City area.
Using 12 years of lightning data from the National Lightning Detection Network and data from hundreds of air pollution stations in the two cities, they were able to determine that in environments with high instability, adding more pollution increases cloud-to-ground lightning strikes.
“Our analysis grouped the lightning flashes into a total of 196,836 thunderstorm events in the Washington DC region, while 310,209 thunderstorms were identified from the flash database for Kansas City,” they said.
“Over 37.7% and 39.2% of all thunderstorm events consisted of over 10 flashes for Washington, DC and Kansas City, respectively.”
“Evidence suggests that warm season thunderstorm environments in benign synoptic conditions are considerably different in thermodynamics, aerosol properties, and aerosol concentrations between the Washington, DC and Kansas City regions,” they added.
“However, it appears that thunderstorm intensity, as measured by flash counts, is regulated by similar thermodynamic-aerosol relationships despite the differences in ambient environments.”
“When examining thunderstorm initiation environments, there exist statistically significant, positive relationships between convective available potential energy and flash counts.”
“Aerosol concentration also appears to be a more important quantity than particle size for lightning augmentation.”
The researchers are now doing similar research on Bangkok, Thailand, a megacity with more pollution than Washington, D.C., and Kansas City and located in a hot, tropical climate.
The results so far are similar, albeit with lightning rates even higher in those storms.
“It looks like no matter where you go in the world, urban pollution is capable of enhancing thunderstorms and lightning,” Professor Bentley said.
The study appears in the journal Atmospheric Research.
_____
Mace Bentley et al. 2024. Toward untangling thunderstorm-aerosol relationships: An observational study of regions centered on Washington, DC and Kansas City, MO. Atmospheric Research 304: 107402; doi: 10.1016/j.atmosres.2024.107402
Source : Breaking Science News