Predicting the effect of anomalous sea ice loss and increasing sea surface temperatures on global storm systems
Azara Mohammadi –
To become a PhD candidate at the University of Alaska Fairbanks, Soumik Basu moved from his home in Kolkata, India to a region infamous for its “below zero” weather: Interior Alaska. Basu left warm weather and his family (not to mention his mother’s cooking) because “The climate is changing, so I wanted to study how these changes in the climate affect the storm activities over the Northern Hemisphere.”
Specifically, Basu came to UAF to understand variability and changes in mid- and high-latitude storms and how it affects weather events. “We know that due to a warming climate, these storms are changing,” Basu explains. “In recent years you can see that there are numerous and intense storms over the U.S. East Coast; increasing storms, snowfalls, freezing rain, and wind gusts… and we [in Alaska] are enjoying the sunny and warm weather!”
So why did Basu travel to the Arctic to understand anomalous weather patterns on the East Coast? He has two motivations, which he describes while sitting in his cubical surrounded by a number of small model dinosaurs. (Basu is a man of many interests and hobbies.)
First, Basu moved to the Arctic in 2009 because, in his own words: “If there is a change in the Arctic it’s going to have an impact on the weather system of the lower-latitudes.”
“Higher temperatures and sea ice decline – all those things affect the weather systems,” explains Basu. This statement leads him to his second reason for moving to the Arctic to study climate: “I chose this department of atmospheric sciences at UAF and the International Arctic Research Center, because their knowledge makes them pioneer scientists in this field: the study of climate variability over the Arctic. So when I got the chance, I came to the Arctic!”
Before Basu made his big move in 2009, he looked up IARC Research Professor, Dr. Xiangdong Zhang online. Zhang studies climate variability, Arctic climate systems, high-latitude and mid-latitude storm systems, and how they affect weather events. “I saw that my research interests, what I wanted to do, matches with his. So I decided to come here,” states Basu.
Zhang and Basu used climate models to study changes and variability in extratropical storms. Extratropical storms usually occur over the mid-latitude, which is 40° to 60° north of the equator and over the Arctic. These storms move across oceans and continents, driven by temperature gradients, and dive warm air toward the poles. Common extratropical storms are generated when colder air from the Arctic encounters a warmer mass of air. This area of encounter is termed a storm “front” and is associated with violent weather.
Using global circulation models (computational modeling), Basu produced an integrated evaluation describing how contributions of anomalous sea surface temperatures and sea ice impact Northern Hemisphereic storm activities. “We wanted to study the impact of this elevated tropical sea surface temperature like El Niño on North American storms because recently we have seen increased storm activities, especially over the East Coast, where they are having lots of snowfalls in winter and spring, and it’s disrupting life,” notes Basu. “So from our study we have found that there is an increase in storm activities over the southern part of North America, including the U.S. East and West Coasts, due to an increase in tropical Pacific sea surface temperatures.”
In order to reach this conclusion through climate modeling, Basu runs “ensembles” with different initial conditions and the same “boundary forcings.” Basu explains that forcings “Shape the climate.” He focused on 2 forcings that are key to understanding the effects of climate change on weather events: sea surface temperature and Arctic sea ice.
Basu explains why he uses computer models, rather than pure observation: “In observation we have only 1 observation for every day or month or hour, but in modeling studies we are able to run ensembles. Running ensembles allows us to clearly identify the signal [result] from such forcing, like how sea surface temperatures are impacting storm activities.” Correlating the result of the same forcing within many different virtual environments or virtual atmospheres helps Basu isolate the statistically significant results caused by the given forcing.
Basu points to the Tropical Pacific and elaborates, “For this area we had 120 ensembles. With a lot of samples [ensembles or runs of the models] we increase the robustness of our results because it makes it statistically significant.”
As an example, Basu displays results of an ensemble focusing on sea surface temperature from December to May. He continues, “Then in the next experiment we fix the sea surface temperature and forced the model with January 1979 to 2008 observed Artic sea ice in five ensembles, where each ensemble is 30 years."
These ensembles were run on supercomputers, provided by the Arctic Region Supercomputing Center. Basu started running his model on the supercomputers Pingo and Midnight that ran at a rate of about 31.8 TFLOPS and 12.02 respectively. As is typical of the technological arena, these systems were replaced by PACMAN in 2011, which runs at a higher rate of FLOPS.
So, in addition to climatology, this climate scientist had to learn a bit of computer programming. For his research, Basu learned about model codes and how to write NCL and FORTRAN code to analyze the output of his model.
Basu’s integrated evaluation of how sea surface temperatures and decreasing sea ice is changing Northern Hemisphere storm activities found that decreasing sea ice results in increased storm activity over the Arctic and decreased storm activity over Eurasia. “Less sea ice is associated with increased surface air temperatures, so it’s warmer over the Arctic, and there is increased precipitation over the Arctic also,” explains Basu. “In the first study we identified the effect of elevated tropical Pacific sea surface temperatures on North American storms, and there we found the storms have shifted southward and the southern part of North America is having more storms.”
Another part of Basu’s integrated study found that declining sea ice in the Arctic is correlated with a general decrease in storm activity. However, though the amount of storms may decrease with sea ice, storm severity increases. Basu calls them “extreme storms” and warns, “Maybe you won’t have many storms but you will have one which is very intense and has high wind speed – very severe.”
Basu plans to return to India to look for a job now that his PhD is completed. “I learned here how to do research. So that will help me in doing any research, wherever I go in the future. The basic principles about how climate works, those things can be applied to any climate system anywhere. I am studying the whole world climate system, so I study everything. The tropics have their own physical processes, but the research skills that I learned here will help me understand the tropical climate systems.”
Basu follows up this statement by confessing that he is looking forward to returning home to India and special meals made by his mother. This climate scientist does not think he will miss the Arctic. “Well, at least …not the winter.”
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