Guest essay by David Archibald
Solar cycle length is one of the more important parameters, though difficult to judge even though the cycle is more than half over. The longer Solar Cycle 24, the colder the climate will be during Solar Cycle 25 according to Friis-Christensen and Lassen theory. The one true indication of the end of a solar cycle and the beginning of the next is the flattening of the heliospheric current sheet. That is likely to be at least four years away.
Figure 1: Heliospheric current sheet tilt angle
Figure 2: Interplanetary Magnetic Field
The interplanetary magnetic field has recovered from the record lows of the Solar Cycle 23/24 transition with a peak of activity post the Solar Cycle 24 maximum to levels equating to the 1970s colling period.
Figure 3: F10.7 Flux 2014 – 2016
For the last 18 months solar activity has been in a disciplined downtrend with well-defined activity bounds. There was a jump up in the lower bound of activity in July 2015 but still maintaining the same slope. What is interesting at the moment is that the F10.7 flux has been in a narrow band between 75 and 79 since October 17th.
Figure 4: F10.7 Flux less the decline
To better understand what was going on during that period of 18 months of disciplined downtrend, Figure 4 above shows the F10.7 flux since the beginning of 2015 with the slope flattened. There is a change in character between the first part of the disciplined downtrend period and the second part, with much less volatility in the latter.
Figure 5: F10.7 Flux 1948 – 2016
Figure 5 shows the whole of the instrumental record for the F10.7 flux. While Solar Cycle 24 is the smallest solar cycle in the record, no apparent climate response has been seen to date apart from the cooling of the North Atlantic water column to 700 metres. The greatest temperature response to changes in solar cycle length is seen in northwest Europe so the North Atlantic water column heat content may prove to be a leading indicator.
Figure 6: Ap Index 1932 – 2016
Activity in the Ap index is backloaded to after Solar Cycle 24 maximum.
Figure 10: Solar Wind Flow Pressure 1971 – 2016
The peaks of the solar wind flow pressure during the current solar cycle are also backloaded to after solar cycle maximum.
Figure 7: Oulu Neutron Count 1964 – 2016
The cause of variation in the neutron count is the strength of the interplanetary magnetic field carried in the solar wind. A weaker magnetic field and solar wind allows more galactic cosmic rays to penetrate to the inner planets of the solar system. The galatic cosmic rays cause a shower of neutrons when they hit atoms in the atmosphere. In turn, those neutrons provide nucleation sites for cloud droplets, increasing cloud cover and the Earth’s albedo. Despite the higher values for the interplanetary magnetic field and the solar wind flow pressure post the solar cycle maximum, the neutron count has risen to the levels characterisitic of the 1970s cooling period.
Figure 8: Solar Dipole from the Wilcox Solar Observatory
It is apparent that a number of aspects of solar activity are not a random walk. That may include the solar dipole which appears to form one sharp peak during each solar cycle with the peak values for at least the last four cycles aligned.
Figure 9: Total Solar Irrradiance 1976 – 2016
Variation of total solar irradence over the solar cycle is said to be inconsequential in affecting climate with the change in neutron count being at least seven times more powerful. The total solar irradiance is down to levels of solar minima prior to the 23/24 minimum.
David Archibald is the author of Twilight of Abundance (Regnery)