Polar vortex breakdown

In January 2019, a pattern of high-altitude winds in the Arctic, better known as the polar vortex, weakened, sweeping frigid air over North America and Europe in the second half of the month. Arctic sea ice extent remained well below average, but temperatures in the far north were closer to average than in past years.

Overview of conditions

Figure 1. Arctic sea ice extent for XXXX 20XX was X.XX million square kilometers (X.XX million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data||Credit: National Snow and Ice Data Center|High-resolution image

Figure 1. Arctic sea ice extent for January 2019 was 13.56 million square kilometers (5.24 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent for January averaged 13.56 million square kilometers (5.24 million square miles). This was 860,000 square kilometers (332,000 square miles) below the 1981 to 2010 long-term average sea ice extent, and 500,000 square kilometers (193,000 square miles) above the record low for the month set in January 2018. January 2019 was the sixth lowest January extent in the 1979 to 2019 satellite record.

The average rate of daily ice growth of 51,200 square kilometers (19,800 square miles) was faster than the long-term average. Ice growth primarily occurred in the Bering Sea and Sea of Okhotsk in the Pacific sector as well as in the Labrador and Kara Seas. Some ice spread to the northeast of Svalbard, while retreating slightly to the northwest of these islands. Total ice extent was tracking at eighth lowest on January 31, with below average extent in nearly all sectors of the Arctic.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of February 5, 2019, along with daily ice extent data for four previous years and the record low year. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2016 in orange, 2014 to 2015 in brown, 2013 to 2014 in purple, and 2011 to 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.||Credit: National Snow and Ice Data Center|High-resolution image

Figure 2a. The graph above shows Arctic sea ice extent as of February 5, 2019, along with daily ice extent data for four previous years and the record low year. 2018 to 2019 is shown in blue, 2017 to 2018 in green, 2016 to 2017 in orange, 2015 to 2016 in brown, 2014 to 2015 in purple, and 2012 to 2013 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Figure 2X. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for XXXmonthXX 20XX. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.||Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division| High-resolution image

Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for January 2019. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Figure 2X. This plot shows the departure from average sea level pressure in the Arctic at the 925 hPa level, in degrees Celsius, for XXXmonthXX 20XX. Yellows and reds indicate higher than average air pressures; blues and purples indicate lower than average air pressures.||Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division| High-resolution image

Figure 2c. This plot shows average sea level pressure in the Arctic in millibars (hPa) for January 2019. Yellows and reds indicate high air pressure; blues and purples indicate low average air pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Arctic temperatures were only slightly above average, contrasting recent Januaries when very warm conditions prevailed. Daily 2 meter air temperatures for the Arctic averaged above 80 degrees North from the Danish Meteorological Institute were just a few degrees above the 1958 to 2002 average, whereas in 2018, temperatures ranged from 4 to 12 degrees Celsius (7 to 22 degrees Fahrenheit) above average. Looking at the 925 hPa level (approximately 2,500 feet above the surface; Figure 2b), temperatures of 1 to 2.5 degrees Celsius (2 to 4.5 degrees Fahrenheit) above the 1981 to 2010 average were the rule over the Beaufort Sea and Canadian Arctic Archipelago, and over the Bering Sea. However, part of the Atlantic side of the Arctic had temperatures near or slightly below average for the month. The atmospheric circulation pattern was unusual, with above average pressure at sea level over a broad area including northern Canada, Greenland, and the northern North Atlantic, and a broad area of below average pressure along the Russian and Siberian Arctic coast. Low pressure also prevailed over the northern Pacific and Bering Sea (Figure 2c).

January 2019 compared to previous years

Figure 3. Monthly XXXXX ice extent for 1979 to 201X shows a decline of X.X percent per decade.||Credit: National Snow and Ice Data Center| High-resolution image

Figure 3. Monthly January ice extent for 1979 to 2019 shows a decline of 3.2 percent per decade.

Credit: National Snow and Ice Data Center
High-resolution image

Overall, sea ice extent during January 2019 increased by 1.59 million square kilometers (614,000 square miles). This was 270,000 square kilometers (104,000 square miles) above the 1981 to 2010 average rate for the month. The linear rate of sea ice decline for January was 46,700 square kilometers (18,000 square miles) per year, or 3.2 percent per decade relative to the 1981 to 2010 average.

Cold shoulder

At left, upper atmosphere winds (70 millibars, about 60,000 feet altitude) on 15 January 2019. North America is in the center of this view. Right, surface air temperatures on 30 January, 2019. For reference, Chicago was -26 C (-15°F) on this morning (dark blue color)

Figure 4. The left image shows atmosphere winds (70 millibars, about 60,000 feet altitude) on January 15, 2019. North America is in the center of this view. The right image shows surface air temperatures on January 30, 2019. For reference, Chicago was -26 degrees Celsius (-15 degrees Fahrenheit) on this morning (dark blue color)

Credit: earth.nullschool.net
High-resolution image

When well developed, the upper atmosphere circumpolar wind pattern, or polar vortex, isolates cold Arctic air in the far north, strengthens the mid-latitude jet stream, and reduces the frequency of frigid air outbreaks into lower latitudes. Early in January 2019, the polar vortex split into several separate closed streams. There was an outbreak of bitter cold air crossing southern Canada, the US Midwest, and the East Coast, during the last week of January. Such events have been popularly termed “invasions of the polar vortex.”

Conditions in the upper US Midwest were colder than any previous winter period in the past two decades. Low temperatures in northern Minnesota and all of Wisconsin on January 30 and 31 were in the -27 to -35 degrees Celsius range (-17 to -31 degrees Fahrenheit). Large areas of Michigan, Ohio, Indiana, Iowa, and the Dakotas reached temperatures below -20 degrees Celsius (-4 degrees Fahrenheit). However, few all-time low temperature records were set during the cold snap. Very mild conditions followed the cold snap in early February.

Arctic change: Fast and furious…and urgent

In a recent review paper (Overland et al., 2019), colleagues from a spectrum of polar geophysics disciplines summarized the many facets of the Arctic’s ongoing transformation, noting that this region, perhaps foremost in the globe, requires a quick adjustment to the pace of climate change. The amplification of global climate change in the Arctic, and the emerging potential for long-term atmospheric and ocean circulation changes, permafrost greenhouse gas release, and the effects of changing snow cover and snowmelt timing, point to serious but hard-to-forecast impacts on global society and infrastructure by the second half of this century.

Antarctic notes

After a rapid December loss and record low extent in early January, Antarctic sea ice extent declined at a slower-than-average rate. On January 31, Antarctic sea ice extent dropped to third lowest on record, tying with 2006 and bested by 2017 and 2018. Sea ice extent was particularly low in the eastern Weddell Sea and the eastern Ross Sea. Over the satellite record, Antarctic January sea ice was increasing at 4,400 square kilometers (1,700 square miles) per year or 0.9 percent per decade, although this was not statistically significant at the 95 percent confidence level. The Antarctic minimum for the year is typically in late February. The Southern Annular Mode, similar to the polar vortex for the southern hemisphere, was in its positive phase, favoring westerly winds around the continent and cool conditions over its ice sheet. This was indeed the case for East Antarctica, where temperatures were 2 to 6 degrees Celsius (4 to 11 degrees Fahrenheit) below the 1981 to 2010 mean, but other parts of Antarctica and the surrounding sea ice areas were near average.

References

Danish Meteorological Institute Arctic temperatures

Overland, J., E. Dunlea, J. Box, R. Corell, M. Forsinus, V. Kattsov, M. S. Olsen, J. Pawlak, L-O Reirson, and M. Wang. 2019. The urgency of arctic change. Polar Science. doi:10.1016/j.polar.2018.11.008