 Previous: Amateur Radio Hurricane Recovery Operations Winding Down |  Next: It's JOTA Time October 15-16! |
SEATTLE, WA, Oct 14, 2005--The fourth quarter of 2005 began nearly two weeks ago, but last week's bulletin failed to mention the average sunspot numbers for the quarter just ended. This is a normal quarterly exercise, as we hope to spot trends in the solar cycle.
Looking at the past two weeks, the average daily sunspot numbers over the past week were up over 10 points to 21.7. Average daily solar flux rose, but also by a slight degree, only 2-1/2 points to 78.4.
From the first quarter of 2003 through the third quarter of 2005, the average daily sunspot number was 120.3, 107.3, 110.2, 99.2, 72.9, 71.3, 69.3, 61, 46.1, 55.7 and 58.
The average daily solar flux for the same period was 134.3, 124.2, 120.8, 137.4, 111.1, 99.5, 111, 104.8, 96.4, 93.1 and 93.6.
We could almost convince ourselves that the cycle has already bottomed out if we look at quarterly sunspot numbers this year. Last year's quarterly sunspot numbers dropped steadily from 72.9 at the first quarter of 2004, to 71.3, 69.3 and 61. 2005 began with a big drop, to 46.1 in the first quarter, then rose to 55.7 and 58. Could this cycle really have hit bottom during the first quarter of 2005?
The NOAA Space Environment Center Preliminary Report and Forecast for October 4 shows the same smoothed sunspot number history and prediction table on page 10 that it has shown for quite some time now. In this table, the sunspot cycle appears to reach minimum sometime between December 2006 and January 2007.
But could it have reached minimum two years earlier? Maybe we should compare the quarterly numbers from the last sunspot cycle bottom, which according to the graph above the page 10 table was in 1996. The quarterly average sunspot numbers from the fourth quarter of 1995 through the third quarter of 1997 were 21.3, 13.1, 13, 12.4, 14.2, 11.3, 25.4 and 37.2.
We can see that the previous sunspot minimum was when the quarterly average numbers were between 11 and 13. This included some long periods of no sunspots at all, such as the five weeks in September and October 1996 when every day the sunspot number was zero. The average daily sunspot number from September 1 through October 31 1996 was only 2.6.
So far this year, the quarterly averages were between 46 and 58--a rather high bottom if it is one. We should probably just chalk this up to the normal variations throughout the solar cycle, which never looks like a smooth, predictable moving line unless data from many days is averaged. I think we should be very surprised if the fourth quarter of 2005 has an average daily sunspot number above 60.
For the upcoming week, solar flux and sunspot values should remain about the same, which is low. Predicted planetary A index for Friday through Monday, October 14-17 is 10, 12, 10 and 5. According to Geophysical Institute Prague, October 18, 19 and 20 should be quiet, October 17 quiet to unsettled, unsettled conditions on October 14 and 16, and unsettled to active conditions this Saturday, October 15.
Ever wonder why the planetary geomagnetic numbers are higher than the mid-latitude numbers? It turns out the planetary numbers are all measured at fairly high latitude. Check the latitudes of the observatories that supply the data for the planetary K index (which is used to calculate the daily planetary A index). The average latitude for observatories in the Northern Hemisphere is 55 degrees. For comparison, note that the United States/Canadian border is at 49 degrees from Manitoba to points west, and 55 degrees latitude is where Hudson Bay turns into James Bay at the northern edge of Ontario. Since geomagnetic disturbances are generally higher at high latitudes, no wonder the planetary geomagnetic indices read so high when activity is up.
For more information concerning propagation and an explanation of the numbers used in this bulletin see the ARRL Technical Information Service Propagation page.
Sunspot numbers for October 6 through October 12 were 28, 31, 24, 16, 11, 25 and 17, with a mean of 21.7. The 10.7 cm flux was 79.5, 78.8, 78.1, 78.9, 79.1, 77.6, and 76.8, with a mean of 78.4. Estimated planetary A indices were 4, 11, 22, 9, 10, 6 and 1 with a mean of 9. Estimated mid-latitude A indices were 2, 11, 16, 7, 7, 5 and 1, with a mean of 7.
Amateur solar observer Tad Cook, K7RA, Seattle, Washington, provides this weekly report on solar conditions and propagation. This report
also is available via W1AW every Friday, and an abbreviated version appears in The ARRL Letter. Readers may contact
the author via e-mail.
| Previous: Amateur Radio Hurricane Recovery Operations Winding Down | Next: It's JOTA Time October 15-16! |