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An analysis of the 2009/2010 cold spell
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It's so Cold, there can't be Global Warming video, below:
It's So Cold There Can't be Global Warming
http://www.youtube.com/watch?v=yDTUuckNHgc&feature=player_embedded
Causes of the Unusually Cold & Snowy 2009~2010 Winter
During the winter of 2009-2010 a rare confluence of known factors in earth’s major climate variability systems (the Arctic Oscillation, El Nino and the Pacific Decadal Oscillation in the Pacific, the Indian Ocean dipole) have influenced the Northern Hemisphere winter from North America across to eastern Eurasia, as far east as China and Korea.
The major protagonist in producing the cold winter conditions of 2009/2010 was the Arctic Oscillation; as the Arctic Oscillation's effects fade then El Nino will come to the fore later in 2010, until that too fades away.
The AO refers to the changes in the strength of the atmospheric pressure (measured at sea level) in the Arctic and the mid-latitudes. It is currently in an extreme negative phase; above-normal pressure over the polar region and below-normal pressure over the mid-latitudes. This results in smaller pressure differences, and these weaker systems allow cold air to flow south, displacing the Jet Stream and resulting in wintry weather across Northern Europe, Northern America and Eurasia.This confluence of climate variability systems, and the strength of the Arctic Oscillation, resulted in extremely harsh, cold winter conditions with heavy snowfall in many regions across the northern hemisphere. (Scroll down to Why the 2019-2010 winter was unusually cold and snowy below for explanation.)
January 5th 2010. Yorkshire From The Air.
The most dominant features have been regions of high pressure - anticyclones or Highs - over Greenland, Scandinavia and Siberia. These anticyclones forced colder air away from the Arctic and down into northern America, western Europe and parts of central and eastern Asia. The Greenland anticyclone blocked the usual path of the Jet Stream, forcing it to swerve well away from its usual course. (See graphic below.)
Image fromTechnorati's Lynn Voedisch blog: Used under fair use/educational/non commercial terms.
The cold many of us experienced was a weather phenomenon, not a climate phenomenon. It is not connected to climate change but is part of earth's natural climate variability. In fact we appear to be experiencing a repeat of the same factors that produced extremely cold winters in 1963 and 1978 (See below). Source.
When thinking of the vast area that forms the northern hemisphere bear in mind that cities and towns in America share one important thing with cities and towns in Europe and Asia - the same line-of-latitude.
e.g. Denver [Colorado] & Philadelphia [between New Jersey and New York] in the USA, Madrid in Spain, Ankara in Turkey, Baku in Azerbaijan, Beijing in China and Hamhung in North Korea are all situated approximately* along latitude 40 degrees north. (* Within onedegree [plus/minus] latitude of the 40 degrees north line-of-latitude. NB: All these countries [and India] are in the northern hemisphere.)
When cold air from the Arctic circle spreads out southwards then all the places named above above can be equally affected; particularly as during this winter they found themselves to the north (cold) side of the Jet Stream as it moved to the south.
In N. America the Arctic air reached as far south as Florida which suffered unaccustomed cold and frosts. This was later followed by the cold air mixing with air coming from the Gulf of Mexico carrying moisture that resulted in snow and ice coating Florida's roadways and fields. (See graphic below.)
Graphic from Accuweather. Used under fair-use/educational/non-commercial terms.
According to records going back to 1950, this is one of the the strongest El Nino combined with the most negative Arctic Oscillation yet seen during a winter. The northern polar region is colder than usual, but the equatorial Pacific is warmer than usual. (see below). Both of those helped produce colder conditions.
Bear in mind it wasn't cold worldwide: The town of Exmouth, in Western Australia, for example recorded record heat of 48.9 degrees C (121.82 degrees F)on the 2nd January 2010. Source.
[FONT=arial,sans-serif]The Australian city of Melbourne sweltered through its hottest night since 1902 on 11th January 2010, with temperatures topping 34 degrees Celsius (93 degrees Fahrenheit). [/FONT](Unsurprising its hot, as it's summer in the summer hemisphere.)
In the northern hemisphere north-east America and Canada, in North Africa, across the Mediterranean through to south-west Asia temperatures are very much above normal in early January 2010 - in many places by more than 5 degrees C (9 degrees F), and in parts of northern Canada by more than 10 degrees C (18 degrees F).
On 8th January 2010 parts of coastal Alaska were warmer than Florida.
[FONT=arial,sans-serif]The anticyclones (high pressure) resulted in an unusually warm Arctic, with air temperatures locally at 5.6 to 8.4 degrees C (10 to 15 degrees F) warmer than they should be in certain areas. [/FONT]
[FONT=arial,sans-serif]If you look at the Greenland region on the two images below - towards the centre of each - that is where the high pressure is. Cold air is being displaced away either side and down towards the mid latitudes.[/FONT]
[FONT=arial,sans-serif]Image above: NASA Earth Observatory. (+ Google Cached)[/FONT]At Goose Bay in Newfoundland on January 7th 2010, temperatures were barely getting below zero, the average minimum for January there should be minus 23 degrees C. (Minus 9.4 degrees F.).
In Canada unseasonably warm weather and heavy rain led to the closure of one of Vancouver's Olympic premier ski venues (January 13th 2010), one month before the 2010 Winter Olympics are scheduled to start, in an attempt to conserve the snow for the games. (See also here.) Vancouver, Seattle and Portland all experienced a winter of rain and wind, but much warmer than usual with temperatures around the 10°C mark.
Bulgaria also experienced record warm temperatures. The thermometer reached 17 degrees C in many places with temperatures in Sofia on January 7th, 2010, soaring up to 14 degrees C (57.2 degrees F); at a time when the country should be blanketed by snow and temperatures be well below freezing.
In Crete on New Year's Day the temperature reached 30°C (86F), a new all-time record for Europe in January.
Although there has been freezing weather in places as far afield as Mexico, Florida, China and the UK; the Arctic, Greenland, much of the Mediterranean and southern Asia have been warmer than usual.
Overall the northern hemisphere winter may turn out to be no colder than in previous years, it's just that the heat is being distributed differently.
All this points to a major reorganisation of atmospheric conditions: particularly over the northern hemisphere, caused by the current positions of anticyclones (high pressure areas) and Lows (low pressure areas) across the northern Atlantic and Arctic. During the coldest part of winter it also altered the path of the Jet Stream that crosses the north Atlantic; it was well to the south of its normal track over western Europe for late December and early January. (See below.)
See also: Washington Post Capital Weather Gang. A virtual tour of the cold (and not so cold).
See also: If It’s That Warm, How Come It’s So Damned Cold? Hansen et al.
See also: New Scientist. Errors and Lies Thrive in Cold Weather.
See also:WeatherOnline: The 'Big' Freeze, 2009-10 - Unprecedented, or What?
Some Quick Facts to Bear in Mind
Warm air carries moisture and comes from the tropics/equator. Cold air is denser and carries much less moisture and originates from our planet's poles. In a high-pressure area air is denser than in areas of lower pressure. The result is that air will move from the high-pressure area to an area of lower density, or lower pressure. Winds usually blow from areas of high air pressure towards areas of low air pressure.
Whenever cold, dry air moves away from the poles it eventually encounters warmer, wetter air moving away from the equator. When warm, moist air meets cold air condensation occurs and precipitation results. If the temperature is at-or-below zero then the precipitation falls as snow.
Why the 2009-2010 Winter Was Unusually Cold and Snowy
An atmospheric pattern developed over the Arctic Circle region that flushed cold air away from the North Pole towards the mid-latitudes, where many of us in the N. Hemisphere live.
This pattern, known as ‘high-latitude blocking’ (caused by the negative phase of the Arctic Oscillation, or -AO) is essentially a large area of high pressure (anticyclone) in the atmosphere over far northern latitudes.
[FONT=arial,sans-serif]Saturday 9th January 2010. A large area of high pressure stretches from Northern Ireland across northern Britain[/FONT]
[FONT=arial,sans-serif]and the North Sea to Scandinavia. [/FONT]
[FONT=arial,sans-serif]High pressure also stretches over Greenland, Baffin Bay and NW Canada.[/FONT]
[FONT=arial,sans-serif]The thicker back lines across the UK indicate the main areas of snow showers. More are over the Atlantic.[/FONT]
[FONT=arial,sans-serif]On this day low pressure in the Mediterranean is spreading active weather fronts northwards across Europe & towards south-east England. [/FONT]
[FONT=arial,sans-serif]Met Office Synoptic Chart. 07.30 on Saturday 9th January 2010.[/FONT][FONT=arial,sans-serif]Below: AO Index (updated daily). January 12th 2010 [/FONT][FONT=arial,sans-serif]Image from US National Weather Service Climate Prediction Centre. Used under fair-use/educational/non-commercial terms.[/FONT]
[FONT=arial,sans-serif]The Arctic Oscillation is part of the North Atlantic Oscillation (NAO), also now in its negative phase.[/FONT]
When the NAO is in its positivephase the storm-track doesn’t bring down the intensely cold air from the Arctic. Instead, it drops into Quebec and the Canadian maritimes; a large subtropical high is set up in the Atlantic which keeps the south-eastern United States warmer than normal.
[FONT=arial,sans-serif]When in NAO is in its negative phase (as during the cold winter spell), the main branch of the jet stream brings the cold, Arctic air down into the Central United States, then down to its south-east. The only warm spots on the continent would be the Canadian Maritimes and [/FONT]Newfoundland [FONT=arial,sans-serif]over to [/FONT][FONT=arial,sans-serif]Greenland.[/FONT]Images from: Wrex.com 13WeatherAuthority blog. Used under fair use/educational/non commercial terms.
High pressure pushes cold air downwards; as that air gets nearer the Earth's surface it's forced outwards and away, sending cold air toward us.
This high-latitude blocking pattern (-AO) was the strongest on record for a December in 2009 - and is continued into January 2010. The pattern consisted of two blocking anti-cyclones:
The first was over Greenland and it prevented (blocking) the usual warmer, damper westerly winds from reaching Europe across the Atlantic, by steering the high-altitude jet stream far to the south of Britain, leaving the country and north-western Europe exposed to winds from Russia, Scandinavia and the Arctic Ocean. This anticyclone also pushed large amounts of cold, Arctic air from the north, southwards, towards the United States. e.g. Below.
Charts above from weatherunderground.com. Image [FONT=arial,sans-serif]used under fair-use/educational/non-commercial terms.[/FONT]The second anti-cyclone was the Siberian anti-cyclone (Siberian High) that was over much of northern Eurasia (during the coldest spell high pressure also stretched from above Northern Ireland, across northern Britain and the North Sea to Scandinavia) and also supplied much cold air to areas further south and east such as eastern regions of the USA, as well as to western Europe and across to China. The Siberian High is an intense, cold anticyclone that forms over eastern Siberia in winter; lasting from late November to early March and is associated with cold air and winters over East Asia.
(NB: during any winter a number of High pressure zones (anti-cyclones) form over high latitude areas.)
Negative Arctic Oscillation (AO) conditions allows Arctic air to spill southwards into eastern North America more readily.
Negative AO winters tend to bring cold winters to Europe (winds were from the north and east) whilst the prevailing storm-track (Jet Stream) moved south towards the Mediterranean Sea.
This brought increased storm activity and rainfall to southern Europe and North Africa.
North Western Europe's prevailing winds generally bring weather from the south-west and west; but during the coldest period the wind blew from the north and east.
This led to increased snowy conditions and also brought sub-zero temperatures to North Western Europe from the Arctic, Scandinavia and Siberia.
Image of the UK covered in snow below taken by Nasa's Terra satellite on 7th Jan. 2010. Photo: NASA. Click here to go to much larger version.The weather that north-western Europe normally gets (brought by the Jet Stream) was diverted south towards Spain and the Mediterranean, where it was unseasonably wet for this time of year. e.g. See chart below.
Screenshot from weatheronline.co.ukImage [FONT=arial,sans-serif]used under fair-use/educational/non-commercial terms. Arrows added by site administrator.[/FONT]
The Jet Stream was over the Mediterranean & N. Africa, hundreds of miles south of its normal position, for a January.
The North Atlantic Oscillation and the Historic Record
The Arctic Oscillation forms part of the larger North Atlantic Oscillation (NAO). It also was in a negative phase (above-normal pressure over Iceland; below-normal pressure over the Azores; in Northern Europe this is usually associated with below-normal temperatures).
The NAO index for the month of December 2009 was -1.93, which is the third lowest NAO index since 1950 for a winter month (December, January, or February).
[FONT=arial,sans-serif]Above: NAO Index. January 17th 2010 [/FONT][FONT=arial,sans-serif]Image from US National Weather Service Climate Prediction Centre. Used under fair-use/educational/non-commercial terms.[/FONT]The only winter months with a lower NAO index were February 1978 (-2.20) and January 1963 (-2.12). January 1963 was one of the coldest months on record in the both United Kingdom and the eastern regions of the USA. Source plus US National Weather Service.
In 1963 anticyclones to the North and East of the UK, brought bitterly cold air over Britain. A depression tracked to the South, and brought heavy snowfalls to England, Wales, and Scotland.
The mean maximum temperatures for January 1963 was more than 5 degrees C (9 degrees F) below average over most of Wales, the Midlands and Southern England, and in some places 7 degrees C below average (12.6 degrees F).
1963 was the coldest winter in the UK for 200 years.
We don't have sufficient records (to my knowledge) to demonstrate that these are similar conditions to those that produced the extremely harsh winter of 1946/47, but it I believe it likely to be the case.
That winter was followed by a summer with temperatures well above average, so there may be something to look forward to.
Looking back, it seems that strong and weak jet streams tend to cluster in groups: a series of mild and stormy winters, followed by three or four cold and snowy ones. We can identify the cold clusters in the past half-century: 1962-65, 1968-70, 1978-82, 1985-87 and 1994-97.
What we can't yet tell is whether the conditions experienced this winter will just be for 2009-10, or will prove to be part of a cluster that extends through winters from to 2009 to 2012? Only time will tell.
Some newspaper reports at the time predicted 30 years of cooling or of such winters, this I believe to be erroneous, if not active disinformation.
See also: What’s Causing the Cold Weather?
See also:WeatherOnline: The 'Big' Freeze, 2009-10 - Unprecedented, or What?0 -
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