Friday, December 14, 2007
ARLP052 Propagation de K7RA
Sunspot 978 made a strong showing this week, and daily sunspot numbers are up as a result. The average daily sunspot number for this week rose over 25 points to 36.7, and average daily solar flux rose over 14 points to 87.2. The sunspot numbers on December 9-11 were 42, 43 and 44. Sunspot numbers haven't been nearly this high since July 14-15 of 2007, when it was 41 both days. The daily sunspot number hasn't been higher since June 2 to June 8 of this year, when it was 45, 58, 58, 63, 47, 59 and 51.
You can make your own animation of the emergence and movement of sunspot 978 with photos on http://www.spaceweather.com. Just click on http://snurl.com/ss978 and in the URL field change /06dec07/ to /07dec07/, hit the Enter key, then change it to /08dec07/, hit Enter, and repeat until you reach /13dec07/ (14dec07 will probably also work by the time you read this bulletin). Now you can use your browser's forward and back keys to animate the sunspot and watch it move. It is a big sunspot.
Geomagnetic activity was very low, although it was slightly unsettled around December 11-12 at northern latitudes. But take a look at the table at, http://snurl.com/geokna. Note the absence of any geomagnetic activity in the far north, represented by the strings of zeros for Alaska's College A and K index from November 30 to December 9. The K index is measured every three hours, or eight times per day. Notice in the 64 readings from 1200z December 1 to 0900z December 9, the College K index rose from 0 to 1 only twice.
Tim Goeppinger, K6GEP of Orange, California wondered why, with the higher sunspot numbers, he didn't see better propagation last weekend in the ARRL 10 Meter Contest. Recently this bulletin mentioned unexpected 10 meter propagation when there were no sunspots. This may be a case where this week's sunspot activity wasn't enough to support F layer propagation at 28 MHz, but perhaps recent 10 meter DX was actually supported by sporadic E propagation.
The US Air Force and the NOAA Space Weather Prediction Center forecast solar flux at 95 for December 14-16, and 90 on December 17-19. This suggests a possible continuation of recent sunspot activity, because sunspot numbers this week were 39-44 while solar flux was 89-94.
They also predict a planetary A index for December 14-20 at 5, 5, 10, 20, 15, 15 and 10, so expect unsettled to active geomagnetic conditions on Monday, December 17. Geophysical Institute Prague predicts quiet conditions December 14-16, active December 17, and unsettled December 18-20.
This week there are a slew of new articles from various sources on solar science and Hinode. Rather than give you a multiple links, let's try something new. Copy and paste or just type http://snurl.com/sunmem1 to your web browser's URL field and hit the Enter key to read the first article. For the second, paste again, but change sunmem1 to sunmem2. Keep up that process through sunmem7 to read all seven articles.
Next week is Winter Solstice in the Northern Hemisphere, on Saturday, December 22. After that the hours of daylight will gradually grow longer, and the increased sunlight will improve propagation on the higher bands. Three months away is the Spring Equinox, and if we have more sunspots by then, so much the better.
In the interim, we can take advantage of the long nights and low geomagnetic activity to enjoy the low bands, 160 and 80 meters.
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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/. Monthly propagation charts between four USA regions and twelve overseas
locations are at http://www.arrl.org/qst/propcharts/.
Sunspot numbers for December 6 through 12 were 29, 24, 36, 42, 43, 44 and 39 with a mean of 36.7. 10.7 cm flux was 78.2, 82.2, 86.9, 88.9, 86.9, 93.4, and 93.9 with a mean of 87.2. Estimated planetary A indices were 1, 1, 0, 2, 8, 12 and 7 with a mean of 4.4. Estimated mid-latitude A indices were 1, 0, 1, 1, 5, 9 and 7, with a mean of 3.4.