Polar Vortex | 10 Jan 2025
Why in News?
A severe winter storm has affected a large part of the US, impacting over 60 million people across 30 states.
- This extreme weather is attributed to the southward expansion of the polar vortex, highlighting its role in causing frigid temperatures and severe storms.
Note: Winter storms are weather events characterized by extreme cold, snow, sleet, or freezing rain, often accompanied by strong winds.
- They form when moist air rises, cools, and condenses into precipitation, with cold temperatures ensuring it falls as snow or ice.
What is the Polar Vortex?
- About: The polar vortex is a large area of low-pressure and cold air that rotates around the Earth’s polar regions.
- The term "vortex" describes the counter-clockwise flow of air that confines colder air near the poles.
- Polar Vortex exists year-round, but it weakens in summer and strengthens in winter.
- Types:
- Tropospheric Polar Vortex: Located at the lowest layer of the atmosphere, from the surface up to 10-15 km, where most weather phenomena occur.
- Stratospheric Polar Vortex: Occurs higher up, between 15 km to 50 km, and is strongest during autumn, disappearing in the summer.
- Its changes are influenced by air movement and heat transfer in the polar region. During autumn, circumpolar winds accelerate, strengthening the vortex and forming a unified, rotating mass of polar air in the stratosphere.
- Mechanism of Extreme Cold: When the polar vortex is strong, it keeps the jet stream stable, preventing cold air from moving south.
- However, when the vortex weakens, a disrupted jet stream (a narrow band of strong winds), which usually moves in a straight line, becomes wavy, allowing Arctic air to flow farther south.
- This disruption leads to extremely low temperatures, severe storms, and extreme weather, including snowfall and freezing rain.
- However, when the vortex weakens, a disrupted jet stream (a narrow band of strong winds), which usually moves in a straight line, becomes wavy, allowing Arctic air to flow farther south.
- Global Warming and Polar Vortex: Researchers state that the Arctic is warming faster than the rest of the planet, a phenomenon known as Arctic amplification.
- This reduces the temperature gradient (rate of change of temperature) between the poles and the mid-latitudes, weakening the polar vortex.
Other Geophysical Phenomenon Similar to Polar Vortex
- Arctic Oscillation (AO): It is a climate pattern affecting winter weather in the Northern Hemisphere. When the Arctic Oscillation (AO) is positive, a strong jet stream directs storms north, limiting cold air outbreaks in the mid-latitudes, while the negative phase shifts the jet stream south, causing cold outbreaks and storms.
- North Atlantic Oscillation (NAO): The NAO measures pressure differences between the Azores High and Subpolar Low, affecting weather patterns in North America and Europe.
- The positive phase of NAO brings warmer, wetter conditions in the US and northern Europe, while the negative phase causes cooler, drier conditions.
