As many regular readers know, I've pointed out several times the incident of the abrupt and sustained lowering of the Ap Index which occurred in October 2005. The abrupt step change seemed (to me) to be out of place with the data, and the fact that the sun seems so have reestablished at a lower plateau of the Ap index after that event and has not recovered is an anomaly worth investigating.

From the data provided by NOAA's Space Weather Prediction Center (SWPC) you can see just how little Ap magnetic activity there has been since. Here's a graph from October 2008 showing the step in October 2005:
Planetary Solar Magnetic Index 1991-2008

However, some have suggested that this event doesn't merit attention, and that it is not particularly unusual. I beg to differ. Here's why.

In mid December I started working with Paul Stanko, who has an active interest in the solar data and saw what I saw in the Ap Index. He did some research and found Ap data that goes back further, all the way to 1932. His source for the data is the SPIDR (Space Physics Interactive Data Resource) which is a division of NOAA's National Geophysical Data Center (NGDC). He did some data import and put it all into a mult-page Excel spreadsheet which you can access here.

I had planned to do more study of it, but you know how holidays are, lot's of things to do with that free time. I didn't get back to looking at it until today, especially after SWPC updated their solar datasets on January 3rd, including the Ap Index. Looking at the data to 1932, it was clear to me that what we are seeing today for levels doesn't exist in the record.

About the same time, I got an email from David Archibald, showing his graph of the Ap Index, graphed back to 1932. Having two independent sources of confirmation, I've decided to post this then. The solar average geomagnetic planetary index, Ap is at its lowest level in 75 years, for the entirety of the record:
Planetary Solar Magnetic Index 1932-2008
© David Archibald
I've added some annotation to the graph provided by Archibald to point out areas of interest and to clarify some aspects of it for the novice reader.

The last time the Ap index was this low was 1933. The December 2008 Ap value of 2, released by SWPC yesterday, has never been this low. (Note: Leif Svalgaard contends this value is erroneous, and that 4.2 is the correct value - either way, it is still lower than 1933) Further, the trend from October 2005 continues to decline after being on a fairly level plateau for two years. It has started a decline again in the last year.

This Ap index is a proxy that tells us that the sun is now quite inactive, and the other indices of sunspot index and 10.7 radio flux also confirm this. The sun is in a full blown funk, and your guess is as good as mine as to when it might pull out of it. So far, predictions by NOAA's SWPC and NASA's Hathway have not been near the reality that is being measured.

The starting gate for solar cycle 24 opened a year ago today, when I announced the first ever cycle 24 sunspot. However in the year since, it has become increasingly clear that the horse hasn't left the gate, and may very well be lame.