| Summary: | The past 51 years northern Europe has experienced nine unusually cold winters, where many temperature records have been set. Two of the three last winters, 2009/10 and 2010/11, were the coldest in many places in southern Sweden since the mid 80’s. However, the coldest winter in southern Sweden was, according to SMHI (Sveriges Meteorologiska och Hydrologiska Institut), the winter of 1962/63, when it on average was about 2˚C colder than the winter of 2009/10. For the winters of 2009/10 and 2010/11 the NAO-index was strongly negative during the major part of the cold period. This lead to studies of the index and during the winters of 2009/10 and 2010/11 a possible correlation between the NAO-index and the total surface pressure of the Northern hemisphere was found. Because of this, this report will be dedicated to studying if the other seven unusually cold winters in northern Europe show proof of a similar correlation. The analysis focuses, based on the NAO-index, the total surface pressure and the temperature as well as a number of other parameters, on determining if the correlation is a recurring phenomenon or not for the unusually cold winters in northern Europe. Based on the analysis, clear indications that a correlation between the NAO-index and the total surface pressure of the Northern hemisphere can be seen. De senaste 51 åren har norra Europa upplevt nio ovanligt kalla vintrar där många temperaturrekord har satts. Två av de tre senaste vintrarna, 2009/10 och 2010/11, var de kallaste på många håll i södra Sverige sedan mitten av 80-talet. Den allra kallaste vintern i södra Sverige var dock enligt SMHI (Sveriges Meteorologiska och Hydrologiska Institut) vintern 1962/63 då det i genomsnitt var cirka 2˚C kallare än vintern 2009/10. För både vintrarna 2009/10 och 2010/11 var NAO-indexet kraftigt negativt under största delen av den kalla perioden. Detta ledde till undersökningar av indexet och under vintrarna 2009/10 och 2010/11 upptäcktes en möjlig korrelation mellan NAO-indexet och det totala yttrycket på ...
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