Research into the air masses that drive changes in our day-to-day weather has been limited by land-based and regional studies, leaving wide gaps in our understanding of these impactful phenomena.
A new paper by a Kent State University geographer has just filled in most of those gaps.
In August, the International Journal of Climatology published an article by Cameron C. Lee, Ph.D., assistant professor in the Department of Geography in the College of Arts and Sciences, titled “The gridded weather typing classification version 2: A global‐scale expansion.” The article describes how a classification system for North America that Lee devised as part of his doctoral dissertation has recently been expanded to map 11 types of air masses across the entire globe, every day for the past 40 years.
“If you think about these air masses as being defined by temperature on one axis and humidity on another axis, then you can get anywhere from humid and warm on one end to cold and dry on the other end, and everything in between,” Lee said. “Or you can have seasonal weather — the weather that you would expect for that location for that time of the year.”
The grid also includes two “transitional” weather types — warm and cold front passages.
Lee said all types of air masses can occur across the globe at any time; his model is designed to show how those occurrences vary from the statistical norms for each location.
Lee said the idea of classifying weather types this way has been around since the 1980s. His model, though, is the first to map air masses globally, including over the oceans.
“It defines what I call these seasonally and geographically relative air masses on a day-by-day basis for the entire globe, in a .5 by .5 latitude and longitude resolution,” he said.
That works out to 259,000 locations, every day from 1979 through August 2019, that Lee has classified into one of these weather types — or four-billion “location-days.” He also updates the grid monthly.
“It sounds like a lot of work, and I guess it was, but it’s not like I have to personally go in and classify four billion things,” he said. “It’s basically a giant computer program that gets the data from National Oceanic and Atmospheric Administration (NOAA) models and plugs it into the algorithm that I have to classify everything.”
Lee has already applied the model toward another paper he recently submitted, comparing the frequency of the three different warm weather types with the three cool types for the entire planet, and how they have changed.
“The initial results do show a dramatic rise in the ratio between warm versus cool types,” Lee said. “I also created another index that looks at what I call the extreme types (hot and humid, hot and dry, cool and humid, cool and dry). We do see a slight increase of those over time as well.”
He said these weather types have a greater impact on human health and ecosystems.
“With climate change, the global mean temperature change is a good indicator that we have climate change happening, but it’s not the mean temperature change really affecting us, it’s the extremes,” Lee said. “But with a change in the mean come more frequent extreme weather situations.”
Lee said his model could also be useful for tracking other weather patterns and events like hurricanes, El Niños, and polar vortices.
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