Guest essay by David Archibald
There are a couple of interesting features of the state of the Sun at the moment. Firstly the Oulu Neutron Count has had a rapid reversal in the last few months:
Figure 1: Oulu Neutron Count 1964 – 2016
The neutron count is looking like the rapid reversal during Solar Cycle 19 which was the start of the 1970s Cooling Period. While we are probably still at least three years to solar minimum, it is approaching the values of minima prior to the last minimum.
Figure 2: Ap Index 1932 – 2016
The peak neutron count during the 23/24 solar minimum was well above the levels of prior minima. That corresponds with the spike down of the Ap Index in late 2009 below what appeared to be a floor of activity.
Figure 3: F10.7 Flux 2014 – 2016
The F10.7 flux appeared to be in a disciplined downtrend during most of 2015. Since August the downtrend slope has remained the same but the range has halved.
Figure 4: Heliospheric Current Sheet Tilt Angle
All that can said from this is that we are still a long way from the heliospheric current sheet being flattened which is the best sign of solar minimum.
Figure 5: Solar Wind Flow Pressure 1971 – 2016
Figure 6: Interplanetary Magnetic Field 1966 – 2016
The IMF and the solar wind flow pressure have run up while the F10.7 flux has turned down.
Figure 7: Hemispheric Sunspot Area 1985 – 2016
The sunspot peak has been later and larger in the southern hemisphere than the northern hemisphere over the last three solar cycles.
Figure 8: Hemispheric Sunspot Area and F10.7 Flux 1985 – 2016
This graph has taken the data from Figure 7 with the sunspot area data plotted cumulatively with the F10.7 flux added. It shows the good correlation between sunspot area and F10.7 flux, which is the best indicator of the level of solar activity.
Figure 9: Solar Polar Magnetic Field Strength by Hemisphere 1976 – 2016
The second interesting thing about the state of the Sun is that the asymmetry evident in Figures 7 and 8 looks like it could increase much further based on the divergence between the north and south solar polar magnetic field strengths.
Figure 10: F10.7 Flux and Oulu Neutron Count
Or perhaps this is just as interesting. Up until 2006, the inverted Oulu neutron count followed the F10.7 flux closely with a lag. They departed in 2006 and now the Oulu neutron count is about 500 counts per minute higher than it had been, relative to the lagged F1-.7 flux.
More at the WUWT Solar Reference Page