A new study out of MIT suggests rising global temperatures are causing energy shifts in Earth's atmosphere that are strengthening midlatitude storms, while weakening other important weather systems over North America, Europe and Asia.
Large storm systems called extratropical cyclones draw energy from processes related to Earth's horizontal temperature gradient – the difference in temperature between our planet's northern and southern latitudes. Larger differences in temperature normally result in stronger cyclones, while the reverse is true for slighter gradients.
These systems are created in regions poleward of Earth's tropical zones, and subsequently sweep over the midlatitude regions. While not as dramatic as tropical cyclones, they are responsible for swift changes in temperature and humidity, and are associated with a wide range of conditions, including rainfall and heavy gusts.
In recent decades, the Arctic has been warming faster than the rest of the Earth, which has effectively shortened the horizontal temperature gradient. The new study set out to discover what effect the Arctic warming might have had on atmospheric energy distribution and storm formation.
Using global temperature and humidity data collected by satellites and weather balloons starting from the 1970s, the researchers created a detailed grid showing these values at various atmospheric heights. They noted the average summertime temperature and humidity in regions between 20 degrees latitude and 80 degrees latitude for June, July and August in each year from 1979 – 2017. This information was then fed into an MIT developed algorithm capable of estimating the amount of energy at various points in the atmosphere that could be used for various weather events.
"We can see how this energy goes up and down over the years, and we can also separate how much energy is available for convection, which would manifest itself as thunderstorms for example, versus larger-scale circulations like extratropical cyclones," comments study co-author and Associate Professor Paul O'Gorman, of MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS).
The scientists discovered that the energy available to fuel large extratropical cyclones had diminished by as much as 6 percent since 1979. Conversely, the energy that drives more localized thunderstorms has risen by roughly 13 percent.
Alongside the destruction wreaked by powerful storms, the weakening of extratropical cyclones presents its own risks.
"Extratropical cyclones ventilate air and air pollution, so with weaker extratropical cyclones in the summer, you're looking at the potential for more poor air-quality days in urban areas," says graduate student at EAPS and study co-author, Charles Gertler. "Moving beyond air quality in cities, you have the potential for more destructive thunderstorms and more stagnant days with perhaps longer-lasting heat waves."
In future the researchers hope to fine tune the methodology so they can estimate how climate change could affect weather systems in specific regions.
The results of the study will be published this week in the Proceedings of the National Academy of Sciences.
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