La Soufriere and the Atlantic hurricane season


You don’t often see something like this happening in Hurricane Alley:



Those early explosions at La Soufriere St. Vincent blasted around 0.5 megatonnes of sulfur dioxide into the atmosphere — the biggest release of this potentially climate-changing gas in the Caribbean since they began keeping records of it. (Global Volcanism Program)

The volcano has calmed down a little since then, going days in between explosions instead of hours, with weaker explosions sending up plumes only half as high (some 26,000 feet now versus 52,000 feet a week ago).

And La Soufriere — French for “sulfur place” — is “only” pumping out about 460 tons of SO2 per day, according to measurements on April 16.

All of this is taking place in what meteorologists call the Atlantic Main Development Region, a breeding ground for hurricanes and tropical storms.



Points to remember: Warm water needed to start a hurricane, and how tall these cyclones can get — topping out near the base of the stratosphere, where it’s usually very cold.


So, this close to the start of hurricane season on June 1st, how will all that ash and sulfur affect the storms?

I looked into it a little bit and found that researchers are asking a different question: can volcanic eruptions in the tropics affect Atlantic hurricanes and other tropical cyclones around the world?

The answers thus far, based on computer models and data gleaned from the historical record as well as two large eruptions in 1982 and 1991, and with many learned qualifications and reservations along the way, seem to be:

  • Yes. (Emanuel et al.; Evan)
  • No. (Camargo and Polvani)
  • Maybe. (Camargo and Polvani; Pausata and Camargo)

Wondering why Camargo and Polvani’s very thorough study is both “no” and “maybe”?

It’s because they couldn’t find evidence of a direct effect in their study but kept the possibility open (see the last paragraph of their discussion).

One reason for the uncertainty, of course, is that, even before you add in a large eruption, the science of Earth’s atmosphere and oceans is insanely complicated (and no, we’re not going to get into it here).

Another reason is that both the 1982 and 1991 eruptions happened at a time when a natural process called ENSO was definitely affecting tropical cyclone formation, including hurricanes in the Atlantic basin.

If you’d rather not think too hard this Sunday morning (very understandable), here are some very colorful animations of the process in selected years: the eastern equatorial Pacific gets warmer than usual (red: El Nino) or colder (blue: La Nina — we’re in the tail end of this part of the ENSO cycle right now).

For what these changes do to our weather, you’ll have to click the ENSO link. It’s pretty amazing!

Tambora’s gaping maw is still impressive. (Image: NASA Johnson, CC BY- NC-ND 2.0)

Getting back to our volcanoes, because ENSO was blurring the 1982 and 1991 picture researchers chose a monster eruption for their computer models: the VEI 7 eruption of Indonesia’s Tambora, in 1815, that caused the infamous and deadly “Year Without A Summer” (and indirectly gave us Frankenstein).

You can see here how Tambora compares to other eruptions.

Tambora 1815 absolutely dwarfed the ongoing eruption at La Soufriere St. Vincent. It was also an order of magnitude larger than Pinatubo in 1991 and two orders of magnitude larger than the 1982 eruption of El Chichon in Mexico.

The boffins use it because a tropical VEI 7 eruption’s global effects on tropical cyclones, if such effects exist, should stand out in computer models no matter what the ENSO thing is doing. And the results should apply to smaller eruptions, too. (Pausata and Camargo)

Do eruptions affect hurricanes?

The researchers who answered “yes” or “maybe” all mention the same effect: fewer hurricanes in the North Atlantic basin.

They find different causes for it, though. Overall, the idea is that large eruptions cool ocean surface and subsurface temperatures and increase air temperatures around and in the lower stratosphere.

This, basically. That’s a shot of Pinatubo’s VEI 6 eruption. (Images: USGS)

Why? For complex reasons.

That is not hypothetical, by the way. Data collected on the 1982 and 1991 eruptions show that it happens, though in ways that are too intricate to go into here.

What no one yet knows is whether those colder sea surface temps from an eruption translate into fewer hurricanes (which run on warm water).

Another unknown are the effects of a warmed stratosphere base — remember, that’s up where it’s normally quite cold and outflow at hurricane cloud tops keeps the storm strong. Could warming up there reduce outflow and weaken or perhaps even shut down the tropical cyclone/hurricane/typhoon? (These are all the same storm; the names for it vary from place to place.)

The takeaway from all this is that La Soufriere’s 2021 eruption to date is definitely not going to have major effects like those of Pinatubo, El Chichon, and Tambora.


To date. La Soufriere St. Vincent is capable of ultraplinian blasts, too. Look at that bottom layer, pre-1700s (actually about 15,000 years ago). Image source, #3.


However, meteorologists are probably monitoring this almost as closely as the volcanologists are. If nothing else, there is much data here that might improve their computer models.

And who knows? Maybe NOAA will mention the eruption when their official forecast comes out in May.

Featured image: Mike Mareen/Shutterstock


Sources:

Altman, J.; Saurer, M.; Dolezal, J.; Maredova, N.; and others. 2021. Large volcanic eruptions reduce landfalling tropical cyclone activity: Evidence from tree rings. Science of The Total Environment, 775: 145899.

Camargo, S. J., and Polvani, L. M. 2019. Little evidence of reduced global tropical cyclone activity following recent volcanic eruptions. npj Climate and Atmospheric Science, 2(1): 1-10.

Emanuel, K.; Solomon, S.; Folini, D.; Davis, S.; and Cagnazzo, C. 2013. Influence of tropical tropopause layer cooling on Atlantic hurricane activity. Journal of Climate, 26(7): 2288-2301.

Evan, A. T. 2012. Atlantic hurricane activity following two major volcanic eruptions. Journal of Geophysical Research: Atmospheres, 117(D6).

Global Volcanism Program. 2021. Report on Soufriere St. Vincent (Saint Vincent and the Grenadines). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 7 April-13 April 2021. Smithsonian Institution and US Geological Survey.

Mann, M. E.; Cane, M. A.; Zebiak, S. E.; and Clement, A. 2005. Volcanic and solar forcing of the tropical Pacific over the past 1000 years. Journal of Climate, 18(3): 447-456.

National Weather Service Climate Prediction Center. 2021. El Nino/Southern Oscillation (ENSO) diagnostic discussion (April 8) https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml

National Weather Service Office, Jackson, MS. 2021. El Nino and La Nina. https://www.weather.gov/jan/el_nino_and_la_nina. Last accessed April 16, 2021.

NEMO SVG. April 16, 2021, 9:30 p.m. La Soufriere Bulletin #65. http://nemo.gov.vc/nemo/index.php/49-news-events/press-release/653-la-soufriere-bulletin-65-april-16-2021-9-30-p-m

Pausata, F. S., and Camargo, S. J. 2019. Tropical cyclone activity affected by volcanically induced ITCZ shifts. Proceedings of the National Academy of Sciences, 116(16): 7732-7737.

Self, S.; Zhao, J. X.; Holasek, R. E.; Torres, R. C.; and King, A. J. 1993. The atmospheric impact of the 1991 Mount Pinatubo eruption. https://pubs.usgs.gov/pinatubo/self/

Stevenson, S.; Otto-Bliesner, B.; Fasullo, J.; and Brady, E. 2016. “El Niño like” hydroclimate responses to last millennium volcanic eruptions. Journal of Climate, 29(8): 2907-2921.

University of the West Indies Seismic Research Centre (UWI-SRC). April 16, 2021. Live update on the La Soufriere eruption in St. Vincent and the Grenadines. https://youtube.com/watch?v=pYCr9E3qxKk

___. Update, April 16, 2021, 6 p.m. https://twitter.com/uwiseismic/status/1383215432144867329?s=20

Wendel, J. and Kumar, M. 2016. Pinatubo 25 years later: Eight ways the eruption broke ground. https://eos.org/articles/pinatubo-25-years-later-eight-ways-the-eruption-broke-ground. Last accessed April 16, 2021.



Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.