The slow moving weather systems that lead to massive snowfalls like the now popularly known Snowmageddon that hit the East Coast of the United States in the winter of 2009-10 are now seen to be more frequent during decades in which the North Atlantic Ocean is warmer than usual.
This, from a new study released by NASA and led by Sirpa Häkkinen, an oceanographer at NASA Goddard Space Flight Center in Greenbelt, Maryland.
The study reanalysed atmospheric data from throughout the 20th century and found that blocking events – an event when one of the jet streams that flow around the Earth in the upper part of the troposphere pinches off a large mass of air for an extended period, and which are responsible for the intense snowfalls – occurred up to 30% more often during the 1930s to the 1960s, and are continuing now in a trend that started in the late 1990s.
Initial assumptions placed the blame at the foot of the North Atlantic Oscillation, or NAO. “The NAO is the usual suspect for all atmospheric changes in the northern hemisphere,” Häkkinen said.
However, since 1996, the NAO has remained in what amounts to a neutral state, while the blocking events have continued occurring more frequently than the average.
So, Häkkinen’s team looked at how the Atlantic Multidecadal Ocean Variability (AMV) was acting during the decades when blocking events were more frequent, and found that there was in fact a linkage between the AMV and increased blocking events.
According to NASA, the team also determined that these short-term blocking events could be altering the ocean currents as well.
A series of connected changes begin because clusters of blocking events can divert the normal track of the storms crossing the Atlantic, which in turn can alter the twisting motion that the wind has on ocean waters, or wind curl. Depending on how wind curl works, it can speed up or slow down the large, circulating currents in the ocean known as gyres. When a blocking event reverses the rotation of the wind curl, the winds push against the direction of the whirlpool-like North Atlantic subpolar gyre, slowing its rotation. A slower, weaker gyre allows subtropical waters that would normally be trapped in the whirlpool-like flow to escape and move northward.
“These warmer and more saline waters then invade the subpolar ocean and cause a series of impacts,” said Peter Rhines, an oceanographer at the University of Washington, Seattle, and co-author of the new study. “They erode the base of glaciers, contributing to the melting of the Greenland ice sheet. And the change in temperature and freshness of the waters can alter subpolar ecosystems, too.”
Studies such as this end up providing scientists and meteorologists with an improved ability to forecast the weather, and model the future climate events of our planet.
“For example, knowing that there’s going to be a potential for more blocking events causing more snowfall would not only help people prepare better for the winter; it would be useful with water resources management,” said Häkkinen.