By now, anyone with even a modest interest in progress of the solar cycle knows that the current period of solar minimum is the "lowest and longest" since 1913.
The run of monthly sunspot numbers for the past year (indeed, 2.5 years) has led the solar science world on slow waltz to Armageddon (or so it seems), not to mention DXers, solar bloggers, climate change skeptics and other interested parties.
Taking the monthly smoothed sunspot numbers from January 2007 to December 2008, you can see where they took a dip, rose again after the dip - only to plunge relentlessly downward . . . no less than three times ! See Graph 1 below.
Projections for the date (month) of the solar cycle minimum, from the various space weather agencies, have been pushed out time after time since 2007. The latest - from our own IPS Radio and Space Services - now has it as April 2010
Having prepared and given a series of presentations on the current solar cycle over the past 12 months, I decided to check the "3-monthly running mean" (a smoothing technique - no 'magic' to it) of sunspot numbers for the past year to see how things were going. The running mean is a way of showing trends in variable data.
The "gold standard" for sunspot number data is the Solar Influences Data Analysis Center (SIDC) in Belgium (http://www.sidc.be
). SIDC issues a series of "relative sunspot numbers" (R), derived from data sent to them by 60-or-so observatories across the world. The numbers given by Tad Cook K7RA in his week ARRL Propagation Bulletin are generally from the US's Space Weather Prediction Center (SWPC) - one of the contributors to the SIDC data set. Our own IPS Radio and Space Services also issues monthly sunspot numbers, which closely track those issued by SIDC.
So I've graphed the 3-monthly running means for the period June 2008 through June 2009, for these three sources of sunspot numbers - and the results are intriguing, indeed. From the figure below, it appears we have two
successive minima, six or seven months apart
- one in August last year, the second either in February (SIDC and IPS figures) or March (SWPC figures).
The one marked RI
is the SIDC data; IPS
is the IPS (Aust) data; and SWO
is the SWPC (USA) data. The 3-month running means are marked with blue spots. Looking at the months around the "dips" in the blue spots, I've place a red bar, which is the mean of the three months across the dips. The vertical scale on each is the smoothed sunspot number running mean.
The SIDC graph (RI) shows the February minima to be lowest (1.1 compared to 1.3 for August 2008).
The IPS graph (IPS) shows the two minima to be the same, although the February figure has been round up (from 1.17 to 1.2), because we can only work to one decimal place.
The SWPC graph (SWO) shows the August 2008 minima to be lowest (1.6 compared with 1.8 for March 2009).
Were we there, yet
Maybe. Remember, it looked like we were there several times before
Perhaps we'll know - for sure - sometime in the last quarter of 2009.
Posted in the interests of intrigue.
73, Roger Harrison VK2ZRH