What is the polar vortex?

Photograph of Chicago during the 2014 polar vortex

This view of Chicago was taken from Diversey Harbor on January 7, 2014, when a trough of the Northern Hemisphere polar vortex looped south across the United States, putting much of the country in a deep freeze. Credit: Edward Stojakovic (Creative Commons, http://creativecommons.org/licenses/by/2.0/)

Guest post by Mark Serreze, NSIDC Director and Professor, Department of Geography, University of Colorado Boulder

Lately there has been much talk about extreme cold weather in the United States and its connection to the polar vortex. Just what is the polar vortex, and how does it affect the lower latitudes? We asked Mark Serreze, NSIDC Director and a specialist in Arctic climatology, to provide an explanation. Here is his response:

A vortex is a region within a fluid where the flow is mostly a rotational motion around a given axis. The Earth’s atmosphere, while a gas, nevertheless behaves broadly as a fluid. The polar vortex is the region of the atmosphere that contains the hemisphere’s cold air, rotating from west to east. In the Northern Hemisphere, the axis of the rotation is generally located in the Arctic. There is also a polar vortex in the Southern Hemisphere, in which the axis of rotation is around the Antarctic continent. This post discusses the Northern Hemisphere polar vortex, recognizing that the same basic processes work in the Southern Hemisphere. Continue reading

Does dusty snow mean less water in the Rockies?

Have you been skiing in the Western U.S. and been surprised by brown snow? We recently talked to a research team that studies these coats of dirt. The dust storms that cause dusty snow appear to be getting bigger, thanks to climate warming drying out this region. Worse, dust on snow may increase flooding and slowly smother water supplies in the southwestern U.S. How bad is this situation and who will be affected by it? Can anything be done? Continue reading

Are Arctic cyclones chewing up sea ice?

Satellite image of the 2012 Arctic cyclone

This satellite image of the Great Arctic Cyclone was taken on August 7, 2012 when the center of the storm rolled into the middle of the Arctic Ocean. (Courtesy LANCE/NASA GSFC)

The Big One

The Great Arctic Cyclone of 2012 lifted out of Siberia on August 2nd, swirling in a counter-clockwise rotation up into the Arctic. As one of the most extreme Arctic cyclones ever recorded, its consumption of an already low sea ice extent raised many concerns. Now Arctic cyclones are garnering attention, but is all the hype warranted?

“People seem to have this thought that all this storminess is unusual,” said Mark Serreze, an Arctic climatologist and center director at NSIDC. “Well it’s not. It simply isn’t. Summer is the time for cyclones.” Arctic summers are not calm. In fact, the months of August and September see a maximum amount of cyclonic activity. Not every summer is very stormy, but overall, the Arctic is the Arctic for a reason. Continue reading

Are we in a snow drought?

The central and southwestern portions of the United States have experienced drought for the past several years. This photograph was taken in mid-February, 2010. By that point in winter, these rows would normally have been fully covered in snow. Photograph credit: Kristy Johnson (http://www.flickr.com/photos/kayaker1204/4359744393/)

In spite of the massive blizzards that have slammed parts of the northeastern United States, much of the country is experiencing a pronounced lack of snow. And where there is snow, it is less than usual. It follows a very low snow year from the previous season, causing people to worry if low snowfall is the new normal.

A previous Icelights post, Arctic sea ice and U.S. weather, discussed possible causes behind the changes in winter weather, trying to see if there are correlations to larger climate changes. Researchers like Jennifer Francis of Rutgers University are exploring the possibility that declining sea ice in the Arctic is altering atmospheric temperatures and weakening the jet stream. This change may shift the Northern Hemisphere storm track, leaving some places unusually snowy, or leaving normally snowy locations dry. Can a few good blizzards help reverse the snow drought across parts of the United States? Or is this string of dry winters yet another symptom of climate change? Continue reading

What caused last summer’s Greenland surface melt?

Data image showing extreme Greenland surface melt in summer 2012

These satellite-derived maps show the extent of surface melt over Greenland’s ice sheet during the summer of 2012. On July 8, about 40 percent of the ice sheet had melted at or near the surface. By July 12, nearly 97 percent of the ice sheet surface had melted. High pressure ridges that persisted over Greenland created a lingering heat dome that caused the extensive melt. Credit: Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory

During the summer of 2012, scientists noticed something unusual in Greenland. On July 8, about 40 percent of the Greenland Ice Sheet surface showed signs of melting. But a mere four days later, 97 percent of the surface was melting, an extent that was unprecedented in the satellite record.

Just how unprecedented was this event? Does it mean that the Greenland Ice Sheet is possibly on the way out, like summer sea ice in the Arctic? Continue reading