New research confirms more and bigger Atlantic storms
Iowa State University
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"Unfortunately, it's not great news for people living in coastal regions," said Christina Patricola, an Iowa State University assistant professor of geological and atmospheric sciences, an affiliate of the U.S. Department of Energy's Lawrence Berkeley National Laboratory in California and a study leader.
"Atlantic hurricane seasons will become even more
active in the future, and hurricanes will be even more intense."
The research team ran climate simulations using the Department of Energy's Energy Exascale Earth System Model and found that tropical cyclone frequency could increase 66% during active North Atlantic hurricane seasons by the end of this century.
(Those seasons are typically characterized by La Niña
conditions -- unusually cool surface water in the eastern tropical Pacific
Ocean -- and the positive phase of the Atlantic Meridional Mode -- warmer
surface temperatures in the northern tropical Atlantic Ocean).
The projected numbers of tropical cyclones could increase by 34% during inactive North Atlantic hurricane seasons. (Inactive seasons generally occur during El Niño conditions with warmer surface temperatures in the eastern tropical Pacific Ocean and the negative phase of the Atlantic Meridional Mode with cooler surface temperatures in the northern tropical Atlantic Ocean.)
In addition, the simulations project an increase in storm
intensity during the active and inactive storm seasons.
The scientific journal Geophysical Research Letters recently
published the findings. Ana C.T. Sena, an Iowa State postdoctoral research
associate, is first author.
"Altogether, the co-occurring increase in (tropical
cyclone) number and strength may lead to increased risk to the continental
North Atlantic in the future climate," the researchers wrote.
Patricola added: "Anything that can be done to curb
greenhouse gas emissions could be helpful to reduce this risk."
Cyclone studies in Cyclone Country
Iowa State is home to the Cyclones and storm sirens are part of
the hype at most athletic contests. Talk of the Cyclones is all over campus.
But North Atlantic tropical cyclones? What are they?
"Tropical cyclone is a more generic term than
hurricane," Patricola said. "Hurricanes are relatively strong
tropical cyclones."
Exactly, says the National Oceanic and Atmospheric
Administration. Tropical cyclone is a general reference to a low-pressure
system that forms over tropical waters with thunderstorms near the center of
its closed, cyclonic winds. When those rotating winds exceed 39 mph, the system
becomes a named tropical storm. At 74-plus mph, it becomes a hurricane in the
Atlantic and East Pacific oceans, a typhoon in the northern West Pacific.
Patricola grew up in the Northeast and can still tell stories
about 1991's Hurricane Bob.
"That was a big one for us in Massachusetts," she
said. "For me, it was very exciting. It really caught my interest."
She was a Weather Channel fanatic through a lot of hurricanes in
the mid-1990s. And that led to studies of geological and atmospheric sciences
at Cornell University in New York, followed by atmospheric science and climate
research at Texas A&M University and Lawrence Berkeley National Laboratory.
Patricola joined the Iowa State faculty in August 2020.
Patricola's research interests include climate dynamics, climate
variability and change, extreme weather events, atmosphere-ocean interactions,
high-resolution climate modeling, land-atmosphere interactions, paleoclimates.
And, tropical cyclones.
Why are tropical cyclone numbers so consistent?
Patricola and another set of collaborators have just published a
second research paper about tropical cyclones. This one is also in Geophysical
Research Letters, with Derrick Danso, an Iowa State postdoctoral research
associate, as first author. The paper examines a possible explanation for the
relatively constant number of tropical cyclones observed globally from year to
year.
Could it be that African Easterly Waves, low pressure systems
over the Sahel region of North Africa that take moist tropical winds and raise
them up into thunderclouds, are a key to that steady production of storms?
Using regional model simulations, the researchers were able to
filter out the African Easterly Waves and see what happened. As it turned out,
the simulations didn't change the seasonal number of Atlantic tropical
cyclones. But, tropical cyclones were stronger, peak formation of the storms
shifted from September to August, and the formation region shifted from the
coast of North Africa to the Gulf of Mexico.
So African Easterly Waves many not help researchers predict the
number of Atlantic tropical cyclones every year, but they do appear to impact
important storm characteristics, including intensity and possibly where they
make landfall.
Both papers call for more study.
"We are," Patricola said, "chipping away at the problem of predicting the number of tropical cyclones."
