Figure 1: Solar Polar Field Strength from Wilcox Solar Observatory

The strength of the solar polar magnetic fields is a bit higher than what it was at the 23/24 minimum, shown by the red bar in Figure 1.

Figure 2: aa Index 1868 – 2019

The aa Index is the longest magnetic instrument record, measuring the average of stations in London and Melbourne. What it shows is that we have left the Modern Warm Period behind and have entered a new cold period with magnetic activity similar to that of the late Little Ice Age when the average of activity was similar to the apparent activity floor of the Modern Warm Period.

Figure 3: Ap Index 1932 – 2019

The Ap Index is similar to the aa Index but is based on data from 13 stations. As Figure 3 shows there was an activity floor of 7 during the Modern Warm Period

Figure 4: Interplanetary Magnetic Field 1966 – 2019

The interplanetary magnetic field also shows the break in activity with the end of the Modern Warm Period in 2006. The second half of Solar Cycle 24 was much stronger than the first half.

Figure 5: F10.7 Flux 2014 – 2019

The F10.7 flux shows that the Sun isn’t completely quiescent yet. Figure 7 following shows that all of the activity in 2019 has come from the northern hemisphere.

Figure 6: Sunspot Area by Solar Hemisphere 1874 – 2019

The chart of hemispheric sunspot area also shows the clear change of amplitude and character in the break-over from the Little Ice Age to the Modern Warm Period.

Figure 7: Sunspot Area by Solar Hemisphere 1985 – 2019

This graph of 11-smoothed sunspot area shows a number of interesting things. Firstly that the solar hemispheres have different amplitudes. Secondly that the timing of peak amplitude of the hemispheres is different. The peak in activity for the northern hemisphere was in December 2011 while it June 2014 for the southern hemisphere, two and a half years later. The peaks also have different trends which can hold for up to three solar cycles. This is most likely related to the orbital period of Saturn which is 29.5 years. The differences in amplitude of the hemisphere is likely due to the major gas planets moving above and below the solar plane.

Figure 7: Hemispheric Sunspot Area 1985 – 2019

This figure shows the cumulative contribution to solar activity by hemisphere with the total closely correlating to the F10.7 flux above its activity floor of 64.

Figure 8: Heliospheric Current Sheet Tilt Angle 1976 – 2019

The solar cycle isn’t over until the heliospheric current sheet has flattened and it is still a way off from flattening, probably at least a year.

Figure 9: Solar Wind Flow Pressure 1967 – 2019

The solar wind flow pressure is where the rubber starts to meet the road in terms of the solar influence on climate. It is the solar wind which pushes against the flux of galactic cosmic rays and changes the flux of particles hitting the Earth’s atmosphere. Solar Cycle 24 started out weak but had a much stronger second half – similar in amplitude to Solar Cycle 23.

Figure 10: Oulu Neutron Count 1964 – 2019

The galactic cosmic rays, some with the energy of a tennis ball, hit oxygen and nitrogen nuclei in the upper atmosphere and produce a cascade of particles, mostly neutrons, that reach as far as the Earth’s surface. On the way through, in the lower troposphere, these neutrons can provide nucleation sites for the formation of cloud droplets. Clouds change the planet’s albedo with more clouds producing cooling.

The peak in neutron count with each solar minimum occurs about a year after solar minimum with this due to the time it takes the solar wind to reach the outer solar system. So the next peak in neutron count should be about two years away. The amplitude of the peak is likely to be about 7000.

David Archibald is the author of American Gripen: The Solution to the F-35 Nightmare