What Are Extratropical Cyclones?

A strong extratropical cyclone formed to the south of Australia in late December 2016. RAMSDIS/NOAA/Wikimedia Commons

Tropical cyclones get so much attention that you might assume they're the only cyclone in town. Admittedly, it's hard not to focus on them since tropical cyclones can become hurricanes or typhoons, depending on where you live.

But there are other kinds of cyclones, and tropical cyclones can become different cyclones as their life cycle expires. These storms are called extratropical cyclones, and they're different than a tropical cyclone, including that they'll form as far north as the Arctic.

Tropical cyclones versus extratropical cyclones

While both types of cyclones are low pressure areas, there are some key differences between the storms.

According to the National Oceanic and Atmospheric Administration's Atlantic Oceanographic and Meteorological Laboratory (AOML), tropical cyclones require several specific conditions to form, including:

  • Ocean waters of around 80 degrees Fahrenheit, often within 300 miles from the equator
  • Rapid cooling at a certain height that allows for the release of heat
  • Moist layers near the troposphere
  • A pre-existing system of disturbed water
  • Low amounts of vertical wind shear (high amounts disrupt storm formation)

Extratropical cyclones form a bit differently and have different overall structures. As their name implies, extratropical cyclones form away from the tropical zones where tropical cyclones originate. They tend to form:

  • Along the U.S. Eastern seaboard, north of Florida
  • From the southern half of Chile down in South America
  • In the waters near England and continental Europe
  • Southeastern tip of Australia
A massive and powerful nor'easter affecting the Northeastern United States on March 26, 2014, at peak intensity.
Nor'easters, like this one seen heading toward the Northeastern U.S. in March 2014, are extratropical cyclones. NOAA/Wikimedia Commons

While tropical cyclones need consistent temperatures across the storm to maintain their power, extratropical cyclones thrive on temperature contrasts in the atmosphere, according to the AOML. Extratropical cyclones are the result of cold and warm fronts meeting, and the differences in temperatures and air pressures create the cyclonic motions. Given their structure, extratropical cyclones look like commas when the two different fronts are both well-developed, a difference from the spiral shape of tropical cyclones and hurricanes.

Either of these types of cyclones can become the other, though it's rarer for the extratropical to become a tropical cyclone. Tropical cyclones more often become extratropical once they pass into cooler waters, and their energy sources shift from that heat condensation to the difference in temperature between air masses. The AOML says that predicting the shifts between the two types is "one of the most challenging forecast problems" we face.

Both types of cyclones can result in fogginess, thunderstorms, heavy rain and strong gusts of wind. However, given how and where extratropical cyclones form, they also can produce intense blizzards. Nor'easters, for example, are extratropical cyclones, particularly those experiencing bombogenesis.

Cyclones in the Arctic

The Great Arctic Cyclone of 2012 captured by satellite
The Great Arctic Cyclone of 2012, seen here on Aug. 6, 2012, started in Siberia and then settled midway between Alaska and the North Pole. NASA/Wikimedia Commons

Data on Arctic cyclones dates back to at least 1948, with satellites gathering information on them since 1979. According to a 2014 study published in the Journal of Climate, Arctic cyclones have increased since 1948, even while other cyclone activity decreased between 1960 and the early 1990s. Such cyclones are more common in the winter than the summer, but that study also noted an uptick in summer cyclones.

If you've heard of Arctic cyclones, that's probably due to the Great Arctic Cyclone of 2012, a particularly powerful storm that formed over the Arctic in August 2012. While summer cyclones tend to be weaker in the Arctic, this one was the strongest summer storm at the time and the 13th strongest overall (regardless of the season) since 1979, according to a 2012 study. It lasted for 13 days, an incredibly long time for an Arctic cyclone, which typically only lasts for around 40 hours or so.

Wintertime cyclones are usually stronger than the summertime ones since the conditions that result in extratropical cyclones — the meeting of the Arctic's colder fronts and the equatorial area's warmer fronts — are at their respective peaks. The recent uptick in summer storms is difficult to pin down, however. Climate change may be one reason since it changes sea ice levels and ocean temperatures.

Speaking to NASA in 2012 regarding the Great Arctic Cyclone, John Walsh, a chief scientist at the University of Alaska Fairbanks, explained the skepticism that climate change was the sole driver.

"This past week's storm was exceptional, and the occurrence of Arctic storms of extreme intensity is a topic deserving closer investigation," he told NASA. "With reduced ice cover and warmer sea surfaces, the occurrence of more intense storms is certainly a plausible scenario. The limitation at present is the small sample size of exceptional events, but that may change in the future."

An extratropical cyclone sits over the Arctic on June 7, 2018
An extratropical cyclone sits over the Arctic on June 7, 2018. It's one of the strongest in the region during the summer in recent memory. NOAA

The future may be here. Another "great" cyclone formed over the Arctic in 2018, this one in early June. Like the 2012 cyclone, this one has demonstrated incredible strength, measured by its central pressure of 966 milibars, a non-standard unit of measure for pressure. The 2012 cyclone reached 963 to 966 milibars.

"Preliminarily, this storm could rank in the Top 10 for Arctic Cyclones in June as well as for the summer (June through August) in strength," Steven Cavallo, a meteorologist at the University of Oklahoma, explained to Earther.

While cyclones in the Arctic may not seem as big a deal as storms over densely populated areas, these Arctic cyclones do bring about changes to the environment. According to the National Snow and Ice Data Center (NSID), extratropical cyclones in the region do three things.

  1. They spread out sea ice, which creates spaces between the ice floes.
  2. They bring on cooler conditions.
  3. They result in more precipitation, which as the NSID notes, is between 40 and 50 percent snow, even in the summer months.

Breaking up the sea ice, in particular, can lead to the scenarios that Walsh described to NASA above, and the 2018 cyclone could potentially move a lot of Arctic sea ice out of the region, according to one scientist who spoke to Earther. With less ice, darker spaces of the open water absorb more sunlight and this can speed up the ice melting process.

As the NSID wrote in 2013, moving sea ice isn't the only factor in play:

Stormy patterns bring on cool conditions and more precipitation, which tends to increase ice extent. However, individual cyclones may start to change the rules, putting more emphasis on ice break up as a factor in ice loss.

In short, summer cyclones in the Arctic may be happening more often, but the reasons why, and their impact on the environment, is still a mystery.