Sudden stratospheric warming has split the polar vortex in two. The polar vortex, which forms and deepens as the atmosphere loses heat to space in the darkness of the long Arctic winter night, was split in two by massive heating from below. A series of intense storms in the far north Pacific intensified a very long wave in the lower atmosphere. Energy on that planet sized wave went upwards from the lower atmosphere around the Himalayas and Tibetan Plateau and broke into the stratosphere, causing major sudden warming. It rapidly reversed the strong cyclonic winds in the stratosphere around the pole, creating a central dome, breaking the vortex into two smaller vortices.
We can see the splitting by making a map of the heights a weather balloon rises to to reach the very low atmospheric pressure of 50 mb. A standard atmosphere is 1013mb.
The polar vortex was intact at 50 millibars (heights in m) on January 1 to 3.
The polar vortex had broken in two (50millibar heights in m) on January 10 to 13.
Major stratospheric warmings have taken place, on average, every other year over the past 50 years. The physics of these warmings is very complicated. Since 1998 these warmings have been more frequent and earlier in the winter. Previously, major warmings typically happened in February. Over the past decade they have happened in December and January, but this one is exceptional on all counts. This stratospheric warming is apparently the strongest ever observed in the first half of January according to the NOAA figure. No one knows why the number of major warmings is increasing but a correlation has been with positive sea surface temperature anomalies and the active phase of the solar cycle. This year the sun is active and there are large positive sea surface temperature anomalies in the north Indian ocean and the north-west Pacific.
The dynamical activity in recent winters reveals that the frequency of MWs (Major Warmings) in the Arctic is increasing (e.g. CharltonPerez et al., 2008). ...
Animation of temperature anomalies at the 30mb pressure surface in the stratosphere shows the magnitude of this massive event.
On average, during 1957/58–1990/91, MWs occurred only once every two Arctic winters (e.g Bancala et al. ´ , 2012; Cohen and Jones, 2011; Andrews et al., 1987). Conversely, no MW occurred in 9 consecutive winters from 1989/90 to 1997/98, except a minor warming in early February 1990 (Manney et al., 2005).
However, there were 7 MWs in 5 out of the 6 winters from 1998/99 to 2003/04. The winter 1999/00 was unusually cold but each other winter was prone to MWs... Furthermore, two MWs were observed in 1998/99 and 2001/02...This warming sequence continued and there were 5 MWs in 5 winters again in 2005/06–2009/10... Many of the MWs in recent years have been atypically early (December/early January) compared to those found before 1990s, which were observed mostly in February.
Major stratospheric warming events like these have a large impact on the weather. The warm air in the stratosphere radiates heat and sinks, then warms as it sinks by compressional heating. It causes a mound of relatively warm air and high pressure to develop around the pole. Cold air is pushed away from the pole, in this case under the two vortices. In the Pacific ocean the dynamic interaction of the cold air with abnormally warm water off of the northeast coast of Japan developed one of the strongest north Pacific storm in many years with a central pressure of 932mb, as low as a major hurricane, and modeled wave heights of over 60 feet.
At its most intense point, the storm had an air pressure reading of about 932 mb, roughly equivalent to a Category 4 hurricane, and more intense than Hurricane Sandy as that storm moved toward the New Jersey coastline in October. (In general, the lower the air pressure, the stronger the storm.) The storm's central pressure plunged by 48 to 49 mb in just 24 hours, making it one of the most rapidly intensifying storms at a mean latitude of 34°N since 1979, according to a data analysis by Ryan Maue of Weatherbell Analytics.
On Tuesday, the storm spanned a staggering 1,440 miles, according to David Snider, a meteorologist at the National Weather Service in Alaska. That's equivalent to the distance between Denver and New York City
The swell will generate massive waves on the north and west shores of the Hawaiian Islands. NOAA's outstanding surf forecaster, Pat Caldwell is forecasting 24 foot wave face heights without the amplifying effects of refraction by the sea floor. In surf spots refraction can double these wave heights. 50 foot wave faces are possible on Friday at outer reefs on Kauai and Oahu.
The vortex over north America has been pushing cold air over the United States. Multiple outbreaks of Arctic air can be expected over the eastern half of the U.S. and Canada over the next ten days. A winter storm developing now over the southern Appalachians is forecast to bring snow to the DC area tomorrow afternoon. Then the storm is predicted to intensify over the north Atlantic. The amplifying energy of the southward displaced vortex over north America are forecast by the GFS model to make the storm "bomb" to a 944mb low south of Greenland. Huge waves are forecast to hit the Atlantic coast of Europe early next week.
In February 2009 a major stratospheric warming and polar vortex splitting event occurred unleashing cold air into the eastern United States and Europe. London, England had its heaviest snow in 20 years. NASA's Earth Observatory has a high res video of the event and a plain language description of what happened.
Meteorologist Ryan Hanrahan predicted this cold outbreak based on the breakdown of the polar vortex 2 weeks ago. Kudos to Ryan for the excellent forecast and the outstanding weather blog.