While sunspots are often cited as the main proxy indicator of solar activity, there is another indicator which I view as equally (if not more) important. The Average Planetary Magnetic index (Ap), the strength of which ties into Svensmark’s cosmic ray theory modulating Earth’s cloud cover. A weaker Ap would mean less cosmic rays are deflected by the solar magnetic field, and so the theory goes, more cosmic rays provide more seed nuclei for clouds in Earth”s atmosphere. More clouds mean a greater albedo and less terrestrial solar radiation, which translates to lower temperatures.
I’ve always likened a sunspot to what happens with a rubber band on a toy balsa wood plane. You keep twisting the propeller beyond the normal tightness to get that extra second of thrust and you see the rubber band start to pop out knots. Those knots are like sunspots bursting out of twisted magnetic field lines.
The Babcock model says that the differential rotation of the Sun (the sun being a viscous fluid, the poles rotate at a slower rate than the equator) winds up the magnetic fields of it’s layers during a solar cycle. The magnetic fields will then eventually tangle up to such a degree that they will eventually cause a magnetic break down and the fields will have to struggle to reorganize themselves by bursting up from the surface layers of the Sun. This will cause magnetic North-South pair boundaries (spots) in the photosphere trapping gaseous material that will cool slightly. Thus, when we see sunspots, we are seeing these areas of magnetic field breakdown.
Sunspots are cross connected eruptions of the magnetic field lines, shown in red above. Sometimes they break, spewing tremendous amounts of gas and particles into space. Solar flares and coronal mass ejections (CME’s) are some examples of this process. Sometimes they snap back like rubber bands. The number of sunspots at solar max is a direct indicator of the activity level of the solar dynamo.
As many of you may recall, a few months ago, I had plotted the Average Geomagnetic Planetary Index (Ap) which is a measure of the solar magnetic field strength but also daily index determined from running averages of eight Ap index values. Call it a common yardstick (or meterstick) for solar magnetic activity.
I’ve updated the graph today, to include July 2008 Ap data as you can see below:
Source data, NOAA Space Weather Prediction Center:
As you can see, the Ap Index has continued along at the low level (slightly above zero) that was established during the drop in October 2005. As of July 2008, we now have 34 months of the Ap hovering around a value between 5 to10, with occasional blips of noise.
Since it is provided in the same dataset, I decided to also plot the smoothed Ap Index.
I also plotted my own 24 month smoothing window plot, shown in magenta.
I also decided to update the plot of the 10.7 centimeter band solar radio flux, also a metric of solar activity. It is in the same SWPC dataset file as the Ap Index, in columns 8 and 9. The smoothed 10.7 CM flux value provided by SWPC has also dropped about the same time continues a downward trend.
I also provided my own 24 month wind smoothed value which is plotted in magenta.
Note the lower flux values during this solar minimum than the last
We continue to remain in a deep solar minimum, and with the forecasts being modified to push back the real “active” start of Solar cycle 24, it remains anybody’s guess as to when the sun will come out of it’s funk.