Patterns in Arctic Weather and Climate
The map of sea level pressure for October 1 to 30, 2010, shows a high-pressure system cenetered over the Beaufort and Chukchi sea and Greenland, and low pressure over the Kara and Barents seas. This pattern tends to bring warm air from lower latitudes into the Arctic. —Credit: National Snow and Ice Data Center courtesy NOAA/ESRL PSD
The unique geography of the Arctic leads to unique weather patterns that reappear in the region year after year. Some weather patterns, such as cyclones or anticyclones, occur in the Arctic as well as other regions. Other weather patterns, like the Arctic Oscillation, are specific to the Arctic. Weather patterns that recur or persist over multiple seasons are called semipermanent highs and lows, because these patterns show up in long-term averages of the regional weather. Learn more about these patterns:
Cyclones, or low-pressure systems, are circular weather patterns that rotate in a counter clockwise direction. In a cyclone, air moves upwards in the center of the pattern, bringing stormy wet weather. In the Arctic, cyclones occur year round, but they tend to happen more in certain places depending on the time of year. Semipermanent lows in the Artic include the Aleutian Low, a low-pressure center that experiences many cyclones and storms in the winter, and the Icelandic Low, a low-pressure center located near Iceland.
Anticyclones are the opposite of cyclones, high-pressure systems that rotate in a clockwise direction. An anticyclone known as the Beaufort High recurs year after year, sitting over the Beaufort Sea and Canadian Archipelago in winter and spring. An anticyclone also frequently appears over Siberia, known as the Siberian High.
Polar lows are small, intense cyclones that form over open ocean during the cold season. From satellite imagery, polar lows can look much like a hurricane, with a large spiral of clouds centered around an eye—for this reason they are sometimes called Arctic hurricanes. Polar lows range in size from around 100 to 500 kilometers (62 to 310 miles) in diameter. Wind speeds average around 50 miles per hour, although they can occasionally reach hurricane strength (64 miles per hour).
Polar lows tend to form when cold Arctic air flows over relatively warm open water. The storms can develop rapidly, reaching their maximum strength within 12 to 24 hours of formation, but they dissipate just as quickly, lasting on average only one or two days.
The semipermanent patterns listed below are centers of action in the Arctic atmosphere, influencing weather patterns in the Arctic and around the world.
- Aleutian Low: This semipermanent low-pressure center is located near the Aleutian Islands. Most intense in winter, the Aleutian Low is characterized by many strong cyclones. Traveling cyclones formed in subpolar latitudes in the North Pacific usually slow down and reach maximum intensity in the area of the Aleutian Low.
- Icelandic Low: This low-pressure center is located near Iceland, usually between Iceland and southern Greenland. Most intense during winter, it weakens and splits into two centers in summer, one near Davis Strait and the other west of Iceland.
- Azores High: The Azores High is a high-pressure pattern that forms in the subtropical Atlantic Ocean. Although it occurs outside the Arctic Ocean, it is linked to the Icelandic Low through the North Atlantic oscillation.
- Siberian High: The Siberian High is an intense, cold anticyclone that forms over eastern Siberia in winter, associated with frequent cold air outbreaks over east Asia.
- Beaufort High: The Beaufort High is a high-pressure center over the Beaufort Sea present mainly in winter.
- North American High: The North American High is a relatively weak area of high pressure that covers most of North America during winter. This pressure system tends to be centered over the Yukon, but is not as well-defined as its continental counterpart, the Siberian High.
Weather maps show the circulation and pressure patterns over one or several days. But maps of sea level pressure can also be averaged over several months or years, to show the average circulation patterns in the atmosphere. These averaged maps remove some of the variability caused by day-to-day weather changes, instead showing longer-term patterns that can affect weather and climate both within and outside of the Arctic.
Researchers compare the relative strengths of semipermanent highs and lows, and report these comparisons in indices such as the North Atlantic oscillation and the Arctic oscillation. These indices have been linked to variability in temperatures and to sea ice conditions in the Arctic.
The box at right lists some important semipernament patterns.
The Arctic Oscillation refers to an opposing pattern of pressure between the Arctic and the northern middle latitudes. Overall, if the atmospheric pressure is high in the Arctic, it tends to be low in the northern middle latitudes, such as northern Europe and North America. If atmospheric pressure is low in the middle latitudes it is often high in the Arctic. When pressure is high in the Arctic and low in mid-latitudes, the Arctic Oscillation is in its negative phase. In the positive phase, the pattern is reversed.
Meteorologists and climatologists who study the Arctic pay attention to the Arctic Oscillation, because its phase has an important effect on weather in northern locations. The positive phase of the Arctic Oscillation brings ocean storms farther north, making the weather wetter in Alaska, Scotland, and Scandinavia and drier in the western United States and the Mediterranean. The positive phase also keeps weather warmer than normal in the eastern United States, but makes Greenland colder than normal.
In the negative phase of the Arctic Oscillation the patterns are reversed. A strongly negative phase of the Arctic Oscillation brings warm weather to high latitudes, and cold, stormy weather to the more temperate regions where people live. Over most of the past century, the Arctic Oscillation alternated between its positive and negative phase. For a period during the 1970s to mid-1990s, the Arctic Oscillation tended to stay in its positive phase. However, since then it has again alternated between positive and negative, with a record negative phase in the winter of 2009-2010.
Left: Effects of the Positive Phase of the Arctic Oscillation. Right:Effects of the Negative Phase of the Arctic Oscillation. —Credit: J. Wallace, University of Washington.