The Gulf Stream And Sunspots

The Gulf Stream is known to be responsible for a considerable part of oceanic heat transport and hence influences sea surface temperatures over substantial parts of the North Atlantic Ocean. A comparison between the meridional excursions of the Gulf

8 The NAO has sometimes been dubbed the "Noisy Atlantic Oscillation''.

NAO & the sun spot number

NAO & the sun spot number

- NAOI monthly mean (11-yearMA)

1900 1950

Time

NAOI spectrogram

NAOI spectrogram

Figure 9.9. (a) A comparison between standardised 11-year low-pass-filtered NAOI (dark grey) and sunspot number (black). Also shown is the annual mean NAOI (light grey "step" type). (b) A spectrogram showing the power density associated with the various timescales. Data from: ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA and the CRU.

Stream just off the American continent and the sunspot number (Figure 9.11) may be used for studying links between solar activity and oceanic circulation. One intriguing observation is the tendency for a northerly displacement of the Gulf Stream after sunspot maxima and before sunspot minima. The big question is whether the pattern is coincidental. If both series are characterised by fluctuations with similar timescales, then a comparison between a small number of cycles may yield an apparent connection between the series. Figure 9.12 gives the power spectrum of the Gulf Stream record. The power spectrum exhibits a spectral peak in the vicinity of 8-11 years which is similar to the solar cycle. This intriguing comparison is no evidence of a relationship between the two series as it stands. In order to establish whether there is a link between solar activity and the Gulf Stream displacement, a physical explanation must be sought: how can the sunspots affect the Gulf Stream position? (Why do they not influence the NAO in the same way?) What sets the preferential timescale of the Gulf Stream latitude? These are important questions which must be answered before a link between the two records can be established.

February sunspots v,s. NAOI

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