Watts Up With That?

Many people that have have an interest in the interaction between the Sun and Earth have been keeping a watchful eye on several metrics of solar activity recently. The most popular of course has been sunspot watching.

The sun has been particularly quiet in the last several months, so quiet in fact that Australia’s space weather agency recently revised their solar cycle 24 forecast, pushing the expected date for a ramping up of cycle 24 sunspots into the future by six months.

On August 31st, at 23:59 UTC, just a little over 24 hours from now, we are very likely to make a bit of history. It looks like we will have gone an entire calendar month without a sunspot. According to data from NOAA’s National Geophysical Data Center, the last time that happened was in June of 1913. May of 1913 was also spotless.

With the current space weather activity level of the Sun being near zero, and the SOHO holographic imaging of the far side of the sun showing no developing spots that would come around the edge in the next 24 hours, it seems a safe bet to conclude that August 2008 will be the first spotless month since June 1913.

Here is the sun today,  at 09:14UTC August 30th:

Click for a very large image

Some people who watch the sun regularly might argue that August wasn’t really spotless, because on August 21st, a very tiny plage area looked like it was going to become a countable sunspot. Here is an amateur astronomer’s photo of the event: Read the rest of this entry »

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.

Click for a larger image

I’ve updated the graph today, to include July 2008 Ap data as you can see below: Read the rest of this entry »