What is the Polar Vortex and Why is it Causing Winter Storms in the US?
The expansion of the polar vortex, a cold air system around the Arctic, is driving a significant cold spell across the United States.
The United States is currently grappling with severe winter storms that are affecting more than 60 million people, particularly in the eastern regions. The extreme cold, with temperatures plunging as low as -50°C (-60°F), is being driven by the expansion of the polar vortex—a vast area of frigid, rotating air around the Arctic—pushing southwards.
This weather phenomenon is causing sub-freezing temperatures to reach as far south as the Gulf Coast and Florida Peninsula, regions that are typically not exposed to such severe cold.
What is the Polar Vortex?
The polar vortex is a large-scale system of rotating cold air that typically sits over the North Pole, moving counterclockwise with winds reaching speeds of up to 155mph (250km/h). It plays a key role in the weather patterns of Northern Hemisphere countries, which are particularly vulnerable to its effects during winter.
There are two main types of polar vortexes: tropospheric and stratospheric.
Tropospheric Polar Vortex: This occurs in the lower layer of the atmosphere, where most weather events happen. It brings milder conditions to northern latitudes.
Stratospheric Polar Vortex: This is the one currently impacting the US, forming around 10-30 miles (16-48 km) above the Earth's surface. It typically forms in the autumn and dissipates by spring. When stable, it keeps the Arctic's cold air contained. However, when weakened, it can send this frigid air further south, resulting in extreme cold spells.
The weakening of the stratospheric polar vortex is often triggered by warm air rising from lower layers of the atmosphere. This disrupts the vortex and allows it to spread, potentially reaching as far south as Florida.
Are Cold Polar Vortexes Common?
While the polar vortex is a recurring seasonal phenomenon, it is not a guarantee every year. The term "polar vortex" gained widespread attention following the severe cold of the 2013-14 winter, which saw record-breaking snowfall and temperatures across Canada and the eastern US.
During this event, major cities like New York, Philadelphia, and Chicago experienced significant snowfalls, with some of the highest accumulations in their histories. Notably, the 2013-14 event caused the Great Lakes to freeze over to an extent not seen in decades, with Lake Michigan reaching its highest ice cover ever recorded at 93.3% on March 8, 2014.
Since then, the term has become part of public discourse, helping people understand extreme winter weather in the Northern Hemisphere.
How Does Climate Change Affect the Polar Vortex?
The relationship between climate change and the polar vortex is an area of ongoing research. Some studies suggest that global warming may weaken the polar vortex, leading to more frequent and intense cold spells.
As the planet warms unevenly, the Arctic region is experiencing temperatures rising faster than other parts of the world. This results in a reduced temperature difference between the warmer mid-latitudes and the colder Arctic, destabilizing the polar vortex and the jet stream—a high-speed air current in the atmosphere.
According to Steven Decker, director of the Meteorology Undergraduate Program at Rutgers University, the polar vortex weakens because the pole is warming faster than other areas. This makes the vortex and the jet stream more vulnerable to being displaced, allowing cold air to spill southward, affecting areas that are typically shielded from such extreme conditions.
Paul Ullrich, an associate professor at the University of California, Davis, further explained that the warming of higher latitudes reduces the contrast between the warmer middle latitudes and the Arctic, causing the jet stream to dip further south. This disruption brings polar air to regions such as Europe and North Asia, as well as North America.
Conclusion
The current winter storms in the United States highlight the impact of a weakened polar vortex, which is sending cold air farther south than usual. While such cold spells are cyclical, research suggests that climate change may be altering the frequency and intensity of these events, making extreme winter weather more common. As the planet continues to warm, understanding the dynamics of the polar vortex will be crucial in predicting and mitigating the effects of such weather patterns.