It has been a top ten coldest winter for the first two months of the year in parts of the central states. After a bit of a roller coaster ride with even a warm day or two (first in many weeks) last week a major stratospheric warming event that began last month is translating down to the mid and lower atmosphere with developing high latitude blocking high pressure. These warmings then cause the cold air to dump to mid-latitudes and dominate for usually 30 days or more.
Stratospheric warmings in mid-winter were shown by Labitzke et al (2005) to be favored during westerly QBOs at solar maxima and easterly QBO at solar minima.
Their findings would suggest no major stratospheric warming should occur this mid-winter given this is a westerly QBO winter with a flux under 70. Yet it is there, it is strong (strongest at some levels in the entire 30 years of record) and is forecast to remain. ( forecast for mid February shown).
Baldwin and Dunkerton (2003) provided an overview of stratosphere-troposphere
dynamical coupling. They also discussed dynamical mechanisms that might communicate
stratospheric circulation and temperature anomalies downward from the stratosphere to the troposphere and surface. They agreed with Labitzke that warmings are favored in westerly QBO solar max years.
You can see the polar warming hs split the polar vortex into a two wave feature with centers over North America and Eurasia.
J. Feynman and A. Ruzmaikin (2003) found that the excitation of the North Annular Mode (NAM) of the wintertime geopotential height anomalies between 10 hPa and 1000 hPa is influenced by solar cycle changes and the effect is highly statistically significant (much as Labitzke and Baldwin and Dunkerton). They also found the influence depends on the phase of the Quasi Biennial Oscillation (QBO). In the early winter for the west QBO and the late winter for the east QBO and that the solar changes affect the NAM (Northern Annular Mode – AO and NAO) in both the stratosphere and the troposphere almost equally.
Interestingly though they found the NAM index was found to be systematically lower for low solar activity. The statistical significance of the results were tested by randomizing the solar data. The probability of obtaining these results by chance is less than one in a million. These results also imply that the NAM index in the troposphere was lowered during the Maunder Minimum in comparison with the current epoch.
Shindell showed how the NAM and NAO were strongly negative in the Maunder Minimum as a quiet sun meant less ultraviolet destruction of ozone, an exothermic process in low and mid latitudes and allowed cold air to dominate much further south kicking the NAM and NAO into a dominant negative phase. Negative NAM/NAO is cold as an be seen from his model here.
The sun is still in its ultralong slumber as the 53, 106, 212 years cycles all head towards there minima the next few decades., making it like the Dalton Minimum, a cold period in the early 1800s (the age of Dickens and snowy London town- like this year)
Clilverd 2006 statistical model versus actual and forecast.
The last four cycles were indeed very similar to late 1700s prior to the Dalton Minimum, which makes sense given the phasing of the 106 and 212 year minima the next few decades.
The next few weeks, as cold expanding high pressure expands south into the lower 48, it will suppress the jet stream and its associated still active storm track well south resulting in a MEMORABLE wintry weather period that will in the end when taken together with the cold in December and January have this winter remembered as an old-fashioned 1960s like winter. Many places deep into the south and east will see heavy snow and ice while unseasonably cold air dominates across the north.
In the end the CPC winter forecast from October 16 based mainly on decadal trends (thought to represent global warming) will be a decided bust. Like the stock market, technical traders will tell you, trends can take you only so far. They invariably reverse.
More cold will occur in the UK and Western Europe, where the warm winter forecast by the UKMO also never materialized. Even the forecasters in the UK have noted some similarity to the 1960s and mentioned the early 1800s. Surprisingly that is what the continuing extremely quiet and an analysis of past cycles suggests – a return to the early
1800s Dalton minimum like weather.
VOLCANISM A POSSIBILTY
Another factor may be volcanic eruptions, am Aleutian volcano the last year added some ash to the high atmosphere in the Polar Regions, as we discussed here, high latitude eruptions lead to blocking which dominated in the summer.
Should Mt Redoubt blow big soon, that would translate into a cooler than normal summer and another cold winter next year with more blocking like we see upcoming even if a weak El Nino developed. Although La Ninas are favored, El Ninos do occur in cold PDO phases but are weaker and briefer thus usually colder. Than again if the sun stays quiet, La Nina may not disappear. It tends to dominate near solar minima.