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Inversions in a vertical profile of the atmosphere paint a picture of what is going on at a level (Altitude) well above what we can feel (weather often beginning at the surface and extending to the troposphere (6-20km), commonly extended to the stratosphere). Meteorologists look at multiple levels above the surface to detail what could be happening in your area.  Photo: An example of a Skew-T/LOG-P chart that depicts many variables in a vertical profile of the atmosphere taken at 1200 UTC on 12/22/2019 from Central Illinois. (Photo from the University Center of atmospheric Research) Warm air advection refers to the transfer of warm air from one region to another, which in turn, leads to warmer temperatures at the surface or well into the atmosphere. In this case, we see temperatures rise well above the surface, which creates an inversion layer. Looking at the Skew-T graph, we notice the slanted blue lines give temperature values in Celsius, and the red line presents a graph of the temperature differences with height. At the very bottom of the graph, the temperature is near freezing (0 degrees Celsius), while slightly above the surface, the temperature is closer to 10 degrees Celsius. Due to present cold air at the surface and the factor of warm air rising, the warm air that is advecting into the new region will rise as it moves in. Often air temperature will decrease with height, but in the case of inversions, the air temperature warms with height. The case stands where warmer air moves into a region and rises higher than the already present warm air, thus creating this inversion effect. During the summer, an inversion can aid in the presence of severe weather as a result of solar heating allowing for the inversion layer to be broken due to rapidly rising air. During the winter, an inversion can be present due to advection of warm air, but topography can play a role in blocking air from rising further or mixing. In the case of mixing, warm air rises and generates a mix of the air that was present above it, which acts to ‘dilute’ the air and dry air can mix with fog, clouds or pollution. This situation of pollution interacting with topography is evident in a photo overlooking Salt Lake City, Utah. We can mistake a layer of white just above the town for low hanging clouds, but in reality, it’s a layer of pollution that is trapped.  Photo: Inversion layer present over Salt Lake City, Utah in the winter months. (Photo courtesy of The Daily Universe) Thanks to the surrounding mountain ranges and the city standing in the valley, the inversion layer is somewhat stagnant in town. Pollution accumulates since it is trapped by the surrounding topography which leads to regular poor air quality. In fact, the population has dealt with premature deaths due to the consistent exposure to pollutants.
Utah is only one example of poor air quality due to surrounding topography. Other towns include Los Angeles, Beijing and Hong Kong that deal with high amounts of pollutants in the air. Constant emissions from vehicles and homes contribute to a growing amount of particulate matter in the air that could be trapped in an inversion layer. Winter is a harsh time for inversions to be present for a lengthy period of time in colder regions. Because of the low amount of solar heating with shorter sunlit hours, the chance of mixing the air at the surface with the air aloft is challenged. Cities have little choice to inhibit the buildup of these pollutants, and the ultimate choice is to reduce emissions for a cleaner environment. Research is underway for further preventative measures that these towns can take to reduce pollution and the effect on the community. To learn about more air quality topics click, here. ©2020 Meteorologist Jason Maska
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