Friday, December 07, 2007

ARLP051 Propagation de K7RA

More sunspots emerged this week, with every December day so far showing spots. In addition to the sunspot numbers listed through Wednesday at the end of this bulletin, Thursday, December 6 had a sunspot number of 29. The daily sunspot number has not been this high since mid-July. Two spots are now visible, 977 and 978, and the total coverage of the solar surface by sunspots on Thursday is four times Wednesday's coverage. Average daily sunspot number for this report is over twice last week's, rising from 5.4 to 11.1. Sunspots will probably continue until at least December 13.

Geomagnetic numbers have been extremely low, with average daily planetary A index dropping from 8.7 to 2, and average mid-latitude A index declining from 6.3 to 1.1 for the week. Check the quarterly geomagnetic indices since October 1 at,, and note the incredibly stable numbers, especially at high and mid-latitudes, around December 2-6. You don't see strings of zeroes such as this during the higher portions of the solar cycle, and it seems perfectly timed with last week's ARRL 160 meter contest. Heightened or unsettled to active geomagnetic conditions are not expected until December 17.

Geophysical Institute Prague predicts quiet conditions December 7-9, quiet to unsettled December 10, unsettled December 11-12, and quiet to unsettled December 13.

This year we've been tracking a 3-month moving average of daily sunspot numbers to help spot trends that may indicate the bottom of the solar cycle. Here are the 3-month averages since December 2005.

Dec 05 40.6
Jan 06 32.4
Feb 06 18.1
Mar 06 27.7
Apr 06 38.5
May 06 39.7
Jun 06 28.9
Jul 06 23.3
Aug 06 23.5
Sep 06 21.2
Oct 06 24.1
Nov 06 23.1
Dec 06 27.3
Jan 07 22.7
Feb 07 18.5
Mar 07 11.2
Apr 07 12.2
May 07 15.8
Jun 07 18.7
Jul 07 15.4
Aug 07 10.2
Sep 07 5.4
Oct 07 3

The average for September, October and November, centered on October, at 3 is the lowest yet for this side of Cycle 23. This number was derived by adding all daily sunspot numbers for those three months, then dividing the sum (270) by the number of days, which is 91. The result is approximately 2.967, very close to 3.

Monthly sunspot number averages for this year, January through November, are 28.2, 17.3, 9.8, 6.9, 19.8, 20.7, 15.6, 9.9, 4.8, 1.3 and 2.9. October's average of 1.3 is lower than September and October of 1996, during the minimum between Cycles 22 and 23. The monthly averages for August through November, 1996 were 20.7, 2.9, 2.3 and 25.6.

A new table of predicted sunspot and solar flux values for Cycle 24 is in this week's Preliminary Report and Forecast of Geophysical Data at, on pages 10-11, December 4 issue. For the past few years the prediction table showed no data beyond this month. The table now runs an additional eight years, through December 2015.

Note the two sets of predicted smoothed sunspot data, reflecting the split consensus among members of the Cycle 24 prediction panel at this year's Space Weather Workshop in Boulder, Colorado. The late decline in Cycle 23 led the group away from an earlier consensus for a strong Cycle 24, and now the panel is split. One faction predicts moderately strong sunspot activity for Cycle 24, the other, moderately weak. You can see from the table of values that the strong camp shows a peak centered near August-November 2011, while the weak cycle faction predicts their peak to occur in May-October 2012.

To get an idea of the relative intensity of these predictions, peruse a table of smoothed sunspot numbers at,, showing over 3,000 months of smoothed sunspot numbers back to July, 1749, nearly one-quarter millennia. I'm not suggesting comparison of the predicted values with anything further back than the past few cycles, but it is there if you need it.

Another view of predicted values for this ending cycle and the next one is at,, updated monthly. Another prediction, this time from the Australian government is at,

Joe Reisert, W1JR of Amherst, New Hampshire sent an informative email concerning "great polar openings on 80 and 40 meters to Europe at our sunrise."

Joe continued, "Some ops may not be aware of this propagation mainly to Scandinavia from Eastern and Central USA (perhaps even Western USA). It has already started with LA6WEA and SM2EKM coming in strong. This path usually lasts through late January. This is the time of year when the path is sort of gray line as the Northern Europeans may not be in total darkness." Joe says signals can be quite strong, often have auroral flutter, and it doesn't take an elaborate station to work them.

This weekend is the ARRL 10-Meter Contest, beginning 0000z Saturday, December 8, ending 2359z Sunday. See, for rules. 10 meters may not seem like a good bet at the bottom of the sunspot
cycle, but there have been surprising openings at times. Mark Madcharo, AB2IW of Schenectady, New York is up for the challenge, and plans on drinking lots of coffee.

K0HZI, Jerry Weihrauch of South Saint Paul, Minnesota was one of several who sent a link to an interesting composite of solar images from SOHO, the Solar and Heliospheric Observatory, one representing each year of the current solar cycle. See it at An image also appears on, a radio monitoring blog by Larry Van Horn, N5FPW of Brasstown, North Carolina. D. Moore sent a link to an article about powerful X-ray jets observed by the Hinode spacecraft. Read it at,

The site is a link to a tool brought to us by Doug McCormack, VE3EFC of Thunder Bay, Ontario. Cormac Propadex keeps track of f0F2, the highest frequency that can be reflected from the ionosphere, at a U.S. Air Force observatory in Italy. f0F2 is observed with an ionosonde, or ionosphere sounder, which beams RF straight up while sweeping upward in frequency, then detecting the highest frequency reflected back. When we estimate MUF, or Maximum Usable Frequency, with a propagation program such as W6ELprop, it is telling us the probable MUF between two points at the ends of a radio communication path. f0F2 measures the MUF for a particular patch of sky over the observer, in this case in Italy.

Cormac Propadex keeps track of the average f0F2 value for every 15 minutes over a 60 day period, then displays the difference between the current f0F2 and the average for that time of day. When I first looked at this, it displayed a value of +42, which translates to an f0F2 420 kHz higher than the average for that time of day over the past 60 days. Currently at 0856z on Friday it reads -89, meaning the f0F2 value is 890 kHz lower than average. A value of +350 would be for a current f0F2 value 3.5 MHz higher than the 60 day average. Also check out Doug's web site at,

If you would like to make a comment or have a tip for our readers, email the author at,

For more information concerning radio propagation, see the ARRL Technical Information Service at, For a detailed
explanation of the numbers used in this bulletin see, An archive of past propagation bulletins is at, Monthly propagation charts between four USA regions and twelve overseas
locations are at,

Sunspot numbers for November 29 through December 5 were 0, 0, 13, 26, 13, 13 and 13 with a mean of 11.1. 10.7 cm flux was 71.2, 71.2, 71.9, 73, 72.6, 73.6, and 75.3 with a mean of 72.7. Estimated planetary A indices were 3, 2, 2, 2, 1, 2 and 2 with a mean of 2. Estimated mid-latitude A indices were 2, 1, 2, 2, 0, 0 and 1, with a mean of 1.1.