Propagation de K7RA

The second magnetically reversed sunspot appeared this week, and this time it remained longer. This is the second sunspot from the new solar cycle 24.

Eventually there will be more of the new reversed sunspots than the old ones from cycle 23, and that would be one way to mark the beginning of the next sunspot cycle.

August has passed, so let's look at some monthly averages of sunspot numbers and solar flux.

The average daily sunspot numbers for the months August 2005 through August 2006 were 65.6, 39.2, 13, 32.2, 62.6, 26.7, 5.3, 21.3, 55.2, 39.6, 24.4, 22.6 and 22.8. Average daily solar flux for the same months was 92.4 , 91.9, 76.6, 86.3, 90.8, 83.4, 76.5, 75.5, 88.9, 80.9, 76.5, 75.8 and 79.

We can use these averages to spot trends, but the sunspot numbers jump around quite a bit. To get a smoother view of the sunspot numbers, you can do a moving average, for instance, over 3 months. This would mean averaging any month's average daily sunspot numbers with the month before and the month after data. To the data above, we can add sunspot numbers for the months April through July 2005.

That allows us to look at a 3-month moving average entered on May 2005 through July 2006. We cannot yet figure a 3-month moving average centered on August 2006, because we don't know what the sunspot numbers for September will be.

So the 3-month moving average from May 2005 through July 2006 is 55.6, 64.6, 64.7, 57.8, 39.3, 28.1, 35.9, 40.5, 31.5, 17.8, 27.3, 38.7, 39.7, 28.9 and 23.3

That is pretty smooth, but we see numbers decline, then rise, and then decline again. An even smoother set of numbers would be 7-month moving averages from July 2005 through May 2006. Those numbers are 50.5, 49.1, 48.7 , 44, 34.9, 28.6, 30.9, 34.7, 33.6, 27.9 and 27.3. Although the numbers rise for January and February 2006, the decline of the cycle is more obvious.

Despite the decline in the sunspot cycle, we will see improved HF propagation over long distances in September. The Autumnal Equinox later this month is a time when sunlight is equally distributed over the northern and southern hemispheres. Expect rising sunspot numbers and solar flux over the next few days, with mostly quiet geomagnetic conditions. The predicted planetary A index for September
1-7 is predicted to be 10, 10, 20, 12, 10, 5 and 5.

If you would like to make a comment or have a tip for our readers, email the author at, k7ra@arrl.net.

For more information concerning radio propagation, see the ARRL Technical Information Service at
http://www.arrl.org/tis/info/propagation.html.

For a detailed explanation of the numbers used in this bulletin, see http://www.arrl.org/tis/info/k9la-prop.html.

An archive of past propagation bulletins is at http://www.arrl.org/w1aw/prop/.

Sunspot numbers for August 24 through 30 were 22, 23, 21, 26, 48, 30 and 19 with a mean of 27. 10.7 cm flux was 78.2, 77.2, 75.7, 78.6, 76.4, 73, and 74.2, with a mean of 76.2. Estimated planetary A indices were 5, 2, 3, 18, 11, 9 and 6 with a mean of 7.7. Estimated mid-latitude A indices were 4, 0, 2, 12, 9, 9 and 5, with a mean of 5.9.

Source: The American Radio Relay League