Of Volcanoes and Hurricanes

Today we are going to talk about volcanoes. And hurricanes. And whether or not there might be any relationship.
For those of you raising one eyebrow in question about the concept of any link between these two things, listen: hurricanes appear to be linked to sea surface temperatures. Volcanic eruptions send sulfur dioxide into the air; this can mix with water vapor and create sulfate aerosols. With a large enough eruption, these aerosols are global, and have a noticeable effect; the aerosols absorb shortwave and long wave radiation (making that part of the atmosphere warmer). The aerosols also have the effect of reflecting more sunlight, so less reaches the surface; both land and sea surface temperatures are cooler. With that change in sea surface temperature, we have our possible link to hurricanes.
Enter today’s article, “Atlantic hurricane activity following two major volcanic eruptions” by Amato T. Evan. Published in the Journal of Geophysical Research in 2012, this article looks at the hurricane seasons after two volcanic eruptions and compares them to the seasons immediately preceding. This comparison is not as easy as one might think, because there are many factors that contribute to the change in hurricanes from year to year and decade to decade.
An ash cloud from Mount Pinatubo, a few days before the eruption in 1991. Credit: United States Geological Survey.
An ash cloud from Mount Pinatubo, a few days before the eruption in 1991. Credit: United States Geological Survey.
The two volcanic eruptions discussed in this work are El Chichón, in April 1982, and Mount Pinatubo in June of 1991. Using collected data on sea surface temperature, hurricane intensity and track, and other factors, the author modeled hurricane seasons before and after these eruptions (these models are known to recreate actual hurricane activity well). One modelling simulation was what ‘would have been’ with no effect of the volcanoes, but only normal seasonal variations, to act as the control. Another simulation was run with the effect of the volcanoes.
There were noticeable differences between pre-volcano and post-volcano hurricanes. The three seasons following each volcanic event had about half the number of storms from the seasons before. The pre-volcano hurricanes were also longer-lived and more intense.
The Atlantic Main Development Region (MDR), a region defined by 8-20 degrees North and 20-65 degrees West, is where many hurricanes have their genesis. In pre-volcano hurricanes, 48% began there, with 23% northwards in the eastern United States region. After the volcanoes, however, this flips nearly on its head, to 20% in the MDR and 52% in the eastern US. Before the volcanoes, 29% of them developed in the Caribbean/Gulf of Mexico region, and 27% of the post-eruptions started there as well. Storms formed in the MDR are usually stronger; the switch to formation in the eastern US region may thus help explain why post-volcano storms were less intense.
A satellite image of Hurricane Isabel in September 2013. Courtesy of National Oceanic and Atmospheric Administration.
A satellite image of Hurricane Isabel in September 2013. Courtesy of National Oceanic and Atmospheric Administration.
These results are not as straightforward as one might hope. As previously mentioned, there are many factors that affect hurricanes. Both 1982 and 1992–the years immediately following the eruptions–featured the weather phenomena known as El Niño. The decrease in storm activity for these years may have been both due to the sulfate aerosols and El Niño (it has been suggested that the eruptions fully or partially caused the following El Niño events, but this is unproven). A weather phenomena with the opposite effects of El Niño, known as La Niña, was also present in 1988, which may further bias the pre-volcano results.
In the end, we cannot be sure if there is a link between large volcanic events and hurricanes. This paper only looked at two volcanoes–the ones large enough, with enough data about them, to really be studied. With the biases and other factors, this study is not enough to draw any full conclusions.

 

Bibliography
Evan, Amato T. “Atlantic hurricane activity following two major volcanic eruptions.” Journal of Geophysical Research: Atmospheres 117.D6 (2012).
Today’s main Article.
National Oceanic and Atmospheric Administration. What is the difference between a hurricane, a cyclone, and a typhoon?  NOAA/National Ocean Service, 10 Oct. 2014. Web.
A webpage on the NOAA site discussing hurricanes/typhoons. Also the source of the second image used in this post.
Newhall, Chris, Hendley II, James W, and Stauffer, Peter H. United States Geological Survey. The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines. United States Geological Survey, 28 Feb. 2005. Web.
A USGS factsheet discussing the Mount Pinatubo eruption. Also the source of the first image used in this post.

 

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