The Sun is slowing down


In my post from yesterday, I highlighted a paragraph from a NASA press release which touched on one of the final findings of the soon to be ended Ulysses spacecraft mission to study the sun:

“Ulysses ends its career after revealing that the magnetic field emanating from the sun’s poles is much weaker than previously observed. This could mean the upcoming solar maximum period will be less intense than in recent history. “

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.

solar-geomagnetic-Ap Index
Click for a larger image

I had noted that there was a curious step function in 2005, almost as if something had “switched off”.

Today, since it is fathers day, and I get to do whatever I want, I chose to revisit this graph. Later I plan to take my children to launch model rockets, but for now, here are some interesting new things I’ve found.

First, I’ve updated the original Ap graph to June 2008 as you can see below.

Click for a larger image

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 June 2008, we now have 32 months of the Ap hovering around a value just slightly above zero, with occasional blips of noise.

Since it is provided in the same dataset, I decided to also plot the smoothed Ap Index. I had noted to myself back in February that the smoothed Ap Index had dropped to minus 1.0. I figured it was just an artifact of the smoothing algorithm, but today that number remains there, and there doesn’t appear to be any change even though we’ve had a bit of noise in March that put the Ap Index back up to 10 for that month.

I also plotted my own 24 month smoothing window plot, shown in magenta.

Click for a larger image

I find it curious that the smoothed value provided by SWPC remains at -1. I figure if it is a software error, they would have noted and fixed it by now, and if they haven’t then perhaps they are standing by the number. Odd. One possibility may be that they are using a 12 month fixed window, instead of a moving window month to month. If so, then why show the -1.0 data values? Put nulls — in the dataset.

UPDATE: Astute reader Jorma Kaskiseiväs points out something I missed. The explanation is in the header for the dataset file, a short note: # Missing data: -1″. I was looking in the companion readme file for an explanation. Thanks for pointing this out. Surprising though that SWPC does not use a running average. Easy to do as I’ve shown.

While I was searching for something that could explain this, I came across this plot from NOAA’s NGDC which was used to illustrate solar storm frequency related to sunspots:

Click for original source image, a larger plot is here via FTP link.

But what I found was most interesting was the data file they provided, which had the number of days in a year where the Ap Index exceeded 40. You can view that data file yourself here via FTP link. The accompanying readme file for the data is also available here.

What is most striking is that since 1932, there have not been ANY years prior to 2007 that have zero data. The closest was 1996:

1996 0 0 0 0 0 0 0 0 0 1 0 0 1

2005 3 0 2 1 3 2 2 2 3 0 0 0 18
2006 0 0 1 2 0 0 0 1 0 0 0 1 5
2007 0 0 0 0 0 0 0 0 0 0 0 0 0
2008 0 0 0 0 0 0

Now we have almost two years.

Here is my plot of the above dataset:

Click for a larger image

I also decided to plot 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. Oddly the smoothed 10.7 CM flux value provided by SWPC also has dropped precipitously and stayed there. I also provided my own 24 month wind smoothed value which is plotted in magenta.

Click for a larger image

Like the smoothed Ap Index, it has also stayed that way a few months. NOTE: The data past Dec 2007 on the blue line from SWPC is not valid. The smoothed 24 month window is.

Either way it appears we continue to slide into a deeper than normal solar minima, one not seen in decades. Given the signs, I think we are about to embark upon a grand experiment, over which we have no control.

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