Would there be severe thunderstorms over North America if the Gulf of Mexico were filled with land?
The eastern half of the U.S is one of the principal hot spots for severe thunderstorm activity, especially tornadoes. The standard explanation is the combination of high terrain to the west and the Gulf of Mexico to the south.
A U.S. National Science Foundation-funded study published in the Journal of Climate by Purdue University scientists largely overturns one-half of this long-standing hypothesis. The scientists used a global climate model to conduct climate simulation experiments testing the hypothesis by "flattening" the North American terrain or "filling in" the Gulf of Mexico with land.
"In our climate system, there are large-scale environmental 'pockets' that harbor hazardous weather events," said Varavut Limpasuvan, a program director in NSF's Division of Atmospheric and Geospace Sciences. "Through novel modeling experiments, this study examined the relative importance of two surface properties, terrain elevation and land-sea contrast unique to this region."
The study shows that the potential for severe thunderstorms depends strongly on upstream elevated terrain but surprisingly weakly on the Gulf of Mexico. Removing elevated terrain substantially reduces severe thunderstorm environments, especially over the continental interior, associated with a cooler and drier atmosphere.
Replacing the Gulf of Mexico with land primarily shifts severe thunderstorm environments slightly eastward from the central Great Plains into Illinois, while reducing severity over southern Texas.
The research makes it clear that there is more to learn about why North America is a hot spot for severe thunderstorms and tornadoes and, more generally, how severe weather may change in the future due to climate change.