Understory captures evidence of temperature inversion in Kansas City
The dense spacing of our weather sensors, and frequent measurements (every second!) means that we can observe natural phenomena that other systems miss. During the past two months we’ve observed multiple occurrences of cool air pools in the low-lying areas of Kansas City due to temperature inversion.
Normally, the temperature of the air in the atmospheric layer nearest the surface of the earth – the troposphere – decreases with elevation. The surface of the earth absorbs energy from the sun, reemitting it as long wave radiation that warms the air near the surface. This warm air rises and cools. During temperature inversion, a cool layer of air becomes trapped underneath a warmer air mass, so the temperature of the air actually increases with elevation.
The inversion layer effectively shuts down convection because the cold air at the surface does not rise. This can cause air quality problems in cities since smog does not dissipate as it usually does. Cities that lie in valleys (like Los Angeles) are particularly affected because surrounding mountains trap the cool air from the sides, while the warm inversion layer caps it from above. Temperature inversion is also the cause when the Grand Canyon fills with clouds, since moisture condenses in the cool air.
Surface inversions, like what we observe in Kansas City, happen because the land temperature drops rapidly without the sun and cools the air directly above it during long nights with little wind. This cold air then sinks into low-lying areas, forming cold pools. We observed this effect a dozen times during March and April, but usually the temperature differences are very weak. However, on April 23rd, the cold pools were very clear.
In the maps below, April 22nd and April 24th exhibit normal conditions for Kansas City. Usually the temperature is fairly constant throughout the city at any given time. On April 22nd between 2 and 3 in the morning, the entire Kansas City metro area was 45°F, and 48 hours later the metro area was 60°F. A temperature inversion formed during night of April 22nd and lasted throughout the morning of April 23rd, with the most obvious effects between 2am and 3am. Cold pools formed in the low-lying areas in Leavenworth, Bonner Springs, southwest of Gladstone, ¬¬and the area between Lee’s Summit, Overland Park, and Independence.
On each night we observe temperature inversion, the cold pools exist in the same areas. The morning of March 30th had even clearer temperature inversion, with strong cold pools in Leavenworth, Gladstone, Bonner Springs, and Overland Park. The cold pools disappear during the day of March 30th, but Kansas City also experienced some temperature inversion during the morning of March 31st, although it was a very weak case. Even during weak temperature inversion, we still find cold pools in the same locations: Leavenworth, Bonner Springs, Gladstone, and Overland Park, extending into Lee’s Summit.
In the graphs below, the elevation and temperature for each RTi station is plotted for this same date range. March 28th, 29th, 31st, and April 1st again represent the normal conditions, in which stations at lower elevations record slightly higher temperatures. The range of temperatures is usually around 5 degrees Fahrenheit. But on March 30th we see evidence of temperature inversion, so stations at lower elevations experience cold pools, and stations at higher elevations measure comparatively higher temperatures. The range of temperatures is closer to 12 degrees, which is an impressive difference for a relatively small area.
We care about temperature inversion in Kansas City because it has negative effects on air quality, trapping smog in the city and causing adverse health effects for people with sensitive lungs. Temperature inversion can also cause freezing rain if the ground is cold enough to freeze water on contact. This creates a layer of ice that can damage property, weigh on tree branches and power lines, and make roadways slick. It is interesting that we see temperature inversion in Kansas City because it is relatively flat, but we can conclude even slight topographic roughness is sufficient to form cold pools. Cities with strong inversions are typically in mountainous areas, but our data show that more attention should be paid to temperature inversions in all cities, even in relatively flat regions.
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