The name is alarming, but we’ve seen it all before. Photo: Thinkstock

Reuters – The prospect of a colder-than-normal winter is enough to keep the public on edge, but add a menacing name like “polar vortex” and a simple forecast seems like an omen of the apocalypse.

Forecasters warned that cold outbreaks over North America linked to the polar vortex may be more likely than usual this winter, with the current cold blast for the Prairies just one sign of the times.

But blaming the polar vortex for any one or series of weather events is somewhat irresponsible as the term often carries negative perceptions despite the fact that by definition, the polar vortex is neither unusual nor extreme.

No one really knew what the polar vortex was until four years ago, when the bitterly cold start to 2014 drove up energy consumption and associated commodity prices in the United States. The media instantly fell in love with its sinister sound, and the term “polar vortex” soon gained notoriety — and misunderstanding.

Buzz-worthy though it sounds, the polar vortex is actually much less exciting. It has always existed and is not always the source of extreme weather. In some ways, it is not even a vortex at all.

But the term will likely be misused and overused so it is important to understand the context.

The term “polar vortex” is not the easiest to understand because its usage varies even within the scientific community. It is short for circumpolar vortex and most broadly refers to the west-to-east airflow that circles the pole in middle and high latitudes.

There are two polar vortexes that meteorologists might be referring to when discussing the topic, especially as it pertains to the Northern Hemisphere. One of them describes a strong flow in the stratosphere above the Arctic Circle.

This stratospheric vortex appears in the winter months due to the sharp temperature differences between the mid-latitudes and the poles. If the stratosphere suddenly warms, the vortex weakens. This may or may not indirectly contribute to a cold weather outbreak in North America, Europe or Asia.

The other polar vortex is the one that primarily influences surface weather patterns and can often be linked to chilly winter blasts. It operates in the upper middle latitudes at a height just below a commercial airliner’s cruising altitude.

This “tropospheric” polar vortex is a basic, year-round feature of Earth’s climate structure. It manifests in a string of high- and low-pressure anomalies — known as ridges and troughs — across the middle latitudes.

The advancement of these pressure centres is largely responsible for the rapidly changing weather we experience in the mid-latitudes of the Northern Hemisphere.

The tropospheric vortex is the one that the media likes to highlight in the wintertime as the culprit of harsh, arctic-like conditions. But this same “vortex” can also be responsible for unusually cool summer weather, though broadcasters never make that attribution.

In fact, scientists have recently suggested that using the term “vortex” in connection with surface weather disturbances is not so useful as it is highly prone to misinterpretation, especially since it may incorrectly imply that a dramatic change in global atmospheric circulation has occurred.

Karen Braun is a market analyst for Reuters. The views expressed here are her own.




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