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    Natural Variation In North Atlantic Ocean Caused Extreme Winters In US And Europe
    By News Staff | April 1st 2014 09:03 PM | 2 comments | Print | E-mail | Track Comments

    The extreme cold weather observed across Europe and the east coast of the US in recent winters is due to to natural, long-term variations in sea surface temperatures, according to a new study published in Environmental Research Letters.

    The researchers from University of California Irvine show that the Atlantic Multidecadal Oscillation (AMO) phenomenon — a natural pattern of variation in North Atlantic sea surface temperatures that switches between a positive and negative phase every 60-70 years — can affect an atmospheric circulation pattern, known as the North Atlantic Oscillation (NAO), that influences the temperature and precipitation over the Northern Hemisphere in winter.

    When the AMO is in its positive phase and the sea surface temperatures are warmer, the study has shown that the main effect in winter is to promote the negative phase of the NAO which leads to "blocking" episodes over the North Atlantic sector, allowing cold weather systems to exist over the eastern US and Europe.

    To arrive at their results, the researchers combined observations from the past century with climate simulations of the atmospheric response to the AMO.

    Correlation of trend in total system energy with corresponding trend in total ocean heat content as a function of trend length. doi:10.1088/1748-9326/9/3/034016

    According to their observations, sea surface temperatures in the Atlantic can be up to 1.5 °C warmer in the Gulf Stream region during the positive phase of the AMO compared to the negative, colder phase. The climate simulations suggest that these specific anomalies in sea surface temperatures can play a predominant role in promoting the change in the NAO.

    Lead authors of the study Yannick Peings and Gudrun Magnusdottir said: "Our results indicate that the main effect of the positive AMO in winter is to promote the occurrence of the negative phase of the NAO. A negative NAO in winter usually goes hand-in-hand with cold weather in the eastern US and north-western Europe."

    The observations also suggest that it takes around 10-15 years before the positive phase of AMO has any significant effect on the NAO. The reason for this lag is unknown; however, an explanation might be that AMO phases take time to develop fully.

    As the AMO has been in a positive phase since the early 1990s, it may have contributed to the extreme winters that both the US and Europe have experienced in recent years.

    The researchers warn, however, that the future evolution of the AMO remains uncertain, with many factors potentially affecting how it interacts with atmospheric circulation patterns, such as Arctic sea ice loss, changes in solar radiation, volcanic eruptions and concentrations of greenhouse gases in the atmosphere.

    The AMO also shows strong variability from one year to the next in addition to the changes seen every 60

    Comments

    MikeCrow
    And the 70's had a positive PDO, and a positive AMO, which caused the temps in the northern hemisphere go up about 3/4 of a degree C, around 2000 the PDO went negative, around the beginning of the so caused AGW "pause", with an expected switch of the AMO to the negative phase imminent.

    Joe Bastardi has been talking about this for most of a decade, good weathermen have noted historical weather patterns to help make their predictions better for a long time. If you've paid attention to weather records, a lot of records broken are about 60 years ago, either the last time they are both negative with minimum temp records or both positive for warming records, like we had in the 90's.

    Now AGW is on top of this pair of cycles(AMO/PDO), but the data we have for temperatures before the 70's is poor, and down right bad prior to the 50's, but the best I can tell from the data Co2 warming is a minimal increase on top of these cycles.

    Why is the impact so much smaller than GCM's and radiative models predict, I'm not sure, maybe we really don't understand it, or maybe slight (because they are slight) changes in water vapor provide some negative feedback. But when the AMO's negative cycle kicks in (if it hasn't already), we're going to have long cold winters, a couple decades worth! The US's winter this year was the coldest since 1917, and apparently over the 4 winter months, Chicago has never been as cold as it was this year.
    Never is a long time.
    "The US's winter this year was the coldest since 1917 ..." Sorry, your information is not correct.

    "The average temperature for the contiguous U.S. during the winter was 31.3°F, 1.0°F below the 20th century average. This winter ranked as the 34th coldest winter on record and the coldest since 2009/10."

    So only coldest since 2009/10. While it was cold in some states, it was warm in others.

    "Above and much above average temperatures were present for Florida and much of the West. California had its warmest winter on record, while Arizona had its fourth warmest. "
    https://www.ncdc.noaa.gov/sotc/national/2014/2