Solar Forcing of Meteorological Phenomena on Earth

The team of Professors Jean-Louis Le Mouel, Vincent Courtillot and colleagues has been particularly inspired and productive of late in terms of publishing papers revealing more evidence and information about how the Sun's variable magnetic activity may impact various terrestrial phenomena, including weather and climate (see for example Kossobokov et al. 2010; Le Mouel et al. 2010b). And their new (13 August 2010) publication adds even more remarkable evidence and insights to the topic.

Figure 1 displays some rather unexpected and surprising correlations between the long-term variation in the amplitude (A) of the solid Earth rotation parameter (here they have adopted its well-detected semi-annual variation) called length-of-day and two candidate solar activity measures: sunspot number (SN) and neutron count (NC, a proxy for incoming galactic cosmic rays), which were obtained from a station in Moscow, Russia. They point out that A and NC are inversely correlated with SN, the solar activity index, which leads A by about 1 year. And since galactic cosmic rays are also inversely related to sunspot number with a delay of 1 to 2 years or so, A is directly correlated to NC.

Figure 1. Correlation between the amplitude of the semiannual oscillation in length-of-day (blue curves with middle panel as detrended data while both top and bottom panels as original data) and various solar activity measures (sunspot numbers and proxy for galactic cosmic rays: red curves) from 1962-2009. A 4-year moving-average filter was used to smooth the data series. Adapted from Le Mouel et al. (2010).

Le Mouel et al. (2010) explain the correlations in Figure 1 as being due to a plausible physical link of the 11-year solar activity cycle to a systematic modulation of tropospheric zonal wind (since winds above 30 km contribute less than 20% of Earth's angular momentum, as proxied by A). They also make the important point that although the IPCC and others usually rule out the role of solar irradiance impact on terrestrial climate because of the small interannual changes in the solar irradiance, such an argument does not apply to the plausible link of the large seasonal incoming solar radiation in modulating the semiannual oscillations in the length-of-day amplitude. Consequently, Le Mouel et al. (2010a) say their paper "shows that the Sun can (directly or indirectly) influence tropospheric zonal mean-winds over decadal to multidecadal time scales." And noting that "zonal mean-winds constitute an important element of global atmospheric circulation," they go on to suggest that "if the solar cycle can influence zonal mean-winds, then it may affect other features of global climate as well, including oscillations such as the NAO and MJO, of which zonal winds are an ingredient [Wheeler and Hendon 2004]." Therefore, "the cause of this forcing," as they describe it, "likely involves some combination of solar wind, galactic cosmic rays, ionosphere-Earth currents and cloud microphysics."

In summation, it is becoming clear there are many ways in which the magnetic activity of the Sun can impact various meteorological phenomena on Earth, including temperature and rainfall. The study of Le Mouel et al. (2010) is another unique contribution in that it shows there are connections of solar activity, through persistent modulation of the zonal wind, to faster or slower rotation rates of the solid Earth. And it must be noted that such contributions are only possible because they are willing to take broad multi-disciplinary approaches to understanding the complex patterns that are contained in different dynamical indices of the Earth. Such objective efforts stand in stark contrast to the near-religious paradigm of atmospheric CO₂ as the predominant driver of climate change, as encapsulated in the UN IPCC reports.

Additional References
Kossobokov, V., Le Mouel, J.-L., and Courtillot, V. 2010. A statistically significant signature of multi-decadal solar activity changes in atmospheric temperatures at three European stations. Journal of Atmospheric and Solar-Terrestrial Physics 72: 595-606.

Le Mouel, J.-L., Kossobokov, V., and Courtillot, V. 2010b. A solar pattern in the longest temperature series from three stations in Europe. Journal of Atmospheric and Solar-Terrestrial Physics 72: 62-76.