Our predictions indicate that the present Cycle 24 is expected to be a low-peak cycle. We conclude that the level of solar activity is likely to be reduced significantly during the next 90 years, somewhat resembling the Maunder Minimum period.
On the Verge of a Grand Solar Minimum: A Second Maunder Minimum? Solar Physics, First online: 30 April 2015
The frequency of volcanic eruptions increases (decreases) slightly around the times of solar minimum (maximum).
Stothers, R.B., 1989, Volcanic eruptions and solar activity. J. Geophys. Res., 94
We examined the timing of 11 eruptive events that produced silica-rich magma from four volcanoes in Japan (Mt. Fuji, Mt. Usu, Myojin-sho, and Satsuma-Iwo-jima) over the past 306 years (from AD 1700 to AD 2005). Nine of the 11 events occurred during inactive phases of solar magnetic activity (solar minimum), which is well indexed by the group sunspot number. This strong association between eruption timing and the solar minimum is statistically significant to a confidence level of 96.7%.
At any given time, about 10-20 volcanoes are erupting on average, and it could be imagined that this number sometimes peaks to about 30-50 erupting volcanoes (on land).
What’s erupting? List & map of currently active volcanoes
There is a simple and inescapably plausible link courtesy of Nikolay Sidorenkov and Paul Vaughan. This does not require nor negate the effects of geomagnetic effect or cosmic rays. I am neither saying anything for or against these effects.
If we imagine the Earth having evolved with a Sun of lower insolation. The atmosphere would be more dense and closer to the surface (without a Sun the Earth would be approaching degeneracy). If, in our imaginary world the Sun increased output then the heating effect upon the atmosphere, irrespective of mechanics, would inflate it against gravity. As the Earth is a rotating inertial frame the atmosphere’s increased extent produces an easterly zonal wind. The extended atmosphere does not have the angular velocity to complete a rotation period in the same time as the surface. It has to describe a larger circle. Given time frictional turbulence within the atmosphere and between the atmosphere and surface would force co-rotation. The result would be an increase in rotation speed of the atmosphere at the cost of reduction in rotation of the solid mass.
Well we already measure this effect.
Zenith cameras positioned around the globe measure the rotating velocity of the Earth relative to fixed points in distant space. The result is differences in length of day measured in milliseconds by atomic clocking.
Increases in insolation inflate the atmosphere. Decreases deflate it. The result is the dominance of the mean zonal wind expressed and measured as atmospheric angular momentum.
Increases in insolation, whether in TSI or spectral (ie UV) inflate the atmosphere and result in a deceleration of the globe as a rotating whole. This force is expressed as a change in the mean zonal wind and becomes a change in oceanic circulation through frictional dissipation. The change in lithospheric rotation is measured by the zenith cameras.
The momentum involved proves that the lithosphere is viscously decoupled from the asthenosphere. A simple order of magnitude deduction makes this a certainty.
To summarise. Inflation or deflation of the atmosphere results in changes in mean zonal wind. This manifests as surface oceanic current changes in circulation and through frictional dissipation. Ultimately the stresses are born by the coupling between the lithosphere and the asthenosphere to conserve momentum. A basic physical requirement.
Therefore rapid changes in insolation result in massive stresses imposed upon the lithosphere in transferring momentum changes through the viscous asthenosphere to the bulk of the rotating mass of the Earth.
Any tectonic weakness will be under greater stress during times of changes in insolation.
Sidorenkov and Vaughan saying:
1. Over time, the earth’s crust and atmosphere will come into some kind of equilibrium, and match speeds as best they can, achieving some kind of “steady-state”
2. when the amount of received solar power changes: either less, or more, the atmosphere cools down or heats up
3. in accordance with the Ideal Gas Law — PV=nRT, the atmosphere will contract or expand, changing it’s angular momentum
4. in accordance with Newton’s law of Conservation of Momentum, [ 1st Law] this will exert a torque on the lithosphere, i.e. Earth’s crust
5. picture the Earth as similar to a spinning medicine ball — a thin ~100 mile thick solid rock “skin”, and a 4,000 mile radius hot molten/fluid rock/iron core, plus the atmosphere as similar to a 1-speed bicycle “friction brake” in contact with the Earth’s surface
6. rock is a marvelous building material — great under compression, not-so-much under shear, which is what happens when it has to exert an equal-and-opposite torque on the contracted or expanded atmosphere
7 this shearing force on the rock lithosphere causes buckling events in the earth’s mantle, hence we get volcanoes when the received solar power changes — both reductions and increases.
A similar phenomenon that may be more familiar is the figure skater’s spin, which may be viewed on T.V. during the winter Olympics.
reductions and increases in solar flux cause reductions and increases in the atmosphere’s moment of inertia respectively.
torques exerted by or on the lithosphere to conserve angular momentum cause shearing forces on the lithosphere / mantle, and hence volcanoes.