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In addition, the Sun is probably main driver of low NAO values since 2008, as shown above. In summation, since 1950, we have seen an intensifying correlation between geomagnetic activity and the NAO index, possibly due to a strengthening stratospheric vortex post 1970 (Thompson, et al 2000), With that being said, what about the QBO and other NAO forcing mechanisms? The solar factors, namely geomagnetic activity and GCR provide a fairly strong argument that NAO values will remain on the negative side for this upcoming winter. The NAO and Ap index curves are very well correlated over the past 40-50 years. The NAO relative maxima periods of the early 60s, mid 70s, early and late 80s, early-mid 90s, and the mid 2000s correlate to the higher Ap values.
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The NAO relative minima periods of the mid 50s, the 60s-early 70s, late 70s, mid 80s, mid/late 90s, and right now correlate to the lower Ap values. If we take a look at the following geomagnetic Ap index graph, its strong correlation to the NAO becomes apparent (geomagnetic Ap index is correlated almost perfectly with the aa index). In terms of correlation with NAO values, geomagnetic activity and GCR have higher correlations than the sunspot curve itself (although the latter is important as well). When comparing the solar sunspot cycles to geomagnetic activity, notice there is a pretty significant lag between the maxima/minima of each. There is likely a connection between increases/decreases in cloud cover over the Atlantic (via variations in GCR) and the NAO.īelow is the comparison of NAO and GCR values since 1950. Thus, surface cloudiness increases and global temperatures generally cool when GCR are high. Since GCR are an ionizing radiation, they act as a sort of nuclei for cloud formation, particularly low level clouds. When geomagnetic activity is lower in conjunction with a weaker solar wind, more GCR can penetrate through the atmosphere. The concept in a nutshell is as follows: in times of high geomagnetic activity, the solar wind is stronger, which prevents a significant amount of galactic cosmic rays from reaching the Earth’s surface. Galactic cosmic rays (GCR) have been shown to have a strong inverse correlation to geomagnetic activity and thus the NAO. For the period 1970-2000, the correlation coefficient for the geomagnetic aa and the NAO was 0.93, an outstanding correlation. Studies have speculated that as the Sun has become more active, with increasing irradiance/output by the mid 1900s, its impact on the troposphere strengthened. However, since then, its impact extended down into the troposphere. Early in the period, particularly prior to 1955, geomagnetic activity had a significant impact on the stratosphere but not the troposphere. Note the figure below a strong correlation was found between the geomagnetic aa index and the NAO index over the past half century. Geomagnetic activity indices measure the affect of solar eruptions on Earth. Dr Theodor Landscheidt, a successful solar forecaster, showed how variations in solar output, solar wind, geomagnetic activity, galactic cosmic rays, among other periodicities, impact the modality of the NAO. Solar eruptions are linked to the North Atlantic Oscillation. What has been causing this plummet in NAO values over the past few years? There are multiple mechanisms at work, and I believe that the Sun is/has ultimately been a major driver of the NAO. The NAO has been consistently negative since the spring of 2008, with only a handful of interruptions on the positive side. Currently: Mostly Sunny: 77F August 27, 2022.