The K7RA Solar Update


Solar activity is rising again, but the average sunspot numbers and solar flux are down, compared with last week. This week, the average daily sunspot number declined more than 14 points to 50.9, and the average daily solar flux was off 7 points to 96.8. The average daily planetary A index rose from 6.1 to 9, and the average mid-latitude A index was about the same, declining from 5.4 to 5.1. Sunspot numbers for February 24-March 2 were 23, 31, 49, 44, 54, 72 and 83, with a mean of 50.9. The 10.7 cm flux was 88.9, 88.2, 90.2, 90.4, 95.8, 110.5 and 113.4, with a mean of 96.8. The estimated planetary A indices were 3, 3, 4, 2, 3, 31 and 17, with a mean of 9. The estimated mid-latitude A indices were 0, 1, 2, 1, 2, 18 and 12, with a mean of 5.1.

You can see daily sunspot and solar flux numbers, updated after 0230 here. Geomagnetic indices are updated 8 times per day here. Our weekly data reports in this bulletin run Thursday through Wednesday, so at the above links you can see that yesterday (Thursday, March 3), the planetary A index dropped from 17 to 12, and the daily sunspot number went from 83 to 71. The most active day for geomagnetic indexes was March 1, with a planetary A index of 31; the planetary K index rose as high as 6 on that day. Polar propagation paths were disturbed, with the College A index (measured near Fairbanks, Alaska) for March 1-3 at 53, 43 and 23.

NOAA and USAF predict solar flux of 120 on March 4-11, 110 on March 12-15, 105 on March 16-17 and 100 on March 18-21. The planetary A index is forecast at 12 on March 4-5, 5 on March 6-13, 7 on March 14-15 and 5 on March 16-21. You can get the daily NOAA/USAF prediction for solar flux and planetary A index here. The forecast is usually updated by 2130 daily. Geophysical Institute Prague predicts unsettled geomagnetic activity March 4-5, quiet to unsettled March 6, quiet March 7, quiet to unsettled March 8-9 and quiet again on March 10.

It looks like good conditions for the ARRL International SSB DX Contest this weekend, or at least much more interesting than the past few years, due to increased solar activity. Along with this comes the greater risk of geomagnetic disruption from solar flares, coronal mass ejections and gusts of solar wind. I received some comments from 80 and 160 meter DXers during the recent minimum, noting that they loved the absence of solar activity because everything was so quiet and stable.

For this year’s DX contest, we are seeing sunspot numbers in the range of 20-100, but for the first 10 days of March 2010, the average sunspot number was 20.1. For 2009 it was 2.4, 2008 it was 3.7, 2007 it was 14.9 and in 2006, it was 14.1.

The monthly average of sunspot numbers for December 2010-February 2011 was 22, 32.2 and 53.5, reflecting the rise in solar activity. The three-month moving average of sunspot numbers centered on January -- an average of all daily sunspot numbers for December 2010 through February 2011 -- was 35.3. The three-month moving average of daily sunspot numbers centered on each month of 2010 was 22.4, 25.7, 22.3, 18.5, 16.4, 20.4, 23.2, 28.9, 33, 35.6, 31 and 30.1. The average centered on January 2011 is back up to the level it was in November 2010, 35.6.

The big news this week was about the solar model explaining the deep solar minimum we’ve just experienced. Thanks to all the readers who sent emails about this. See the story here, here, here and here.

Jonathon Ballard, KI4UKF, lives in Stokes County, North Carolina, less than 10 miles south of the Virginia state line. On Wednesday, March 2 at 1655 (just before noon local time), he heard Claudio Costa, LW2ECC (Argentina), calling CQ on 2 meter FM, on 144.48 MHz. KI4UKF was using a Moxon wire antenna tacked to a wall, and said the signal was steady for several minutes at about S6, then faded away. He e-mailed Claudio, who confirmed the transmission. Claudio was using three 5/8 wave verticals and 160 W.

John Shew, N4QQ, of Silver Spring, Maryland was in Curacao for the ARRL DX CW Contest and operated at PJ2T. He had some interesting observations about trans-equatorial propagation on 6 meters into South America: “Thursday evening around 8 PM (0000 February 19), W9VA and I decided to check 6 meters, looking south for TE propagation. The equipment at PJ2T is a Yaesu FT-2000 and a M2 5-element at 70 feet with a clear shot over water to South America. Much to our joy, the band was full of LU beacons at S9 strength. At 0015, we tuned up to 50.110 and I called CQ using the call PJ2/N4QQ. Over the next 15 minutes, I worked 16 stations in 14 grid squares. Signal strengths were S7-S9 plus. “We kinda worked the band empty after 15 minutes but it was still open, but there were no more stations calling us so we moved back over to the HF bands.

“It was a great thrill for me to experience TE propagation for the first time after reading about it many times in the ARRL VHF column over the last 50 years. Signals sounded slightly hollow, but were quite strong with no obvious fading. The band appeared to open to all areas at once, with no obvious flashlight effect, experienced during E-skip. I plotted the grid squares I worked, and they fall in a band about 600 miles deep between 2700 and 3300 miles to the south, crossing the entire South American continent. The plotted skip zone appears to slightly skew from southwest to northeast, with stations to the west farther south than those to the east.

“As I have no experience with TE, I don’t know if this propagation is common for this time of year, or if it occurs throughout the year or if it is enhanced by recent solar events. Solar flux peaked somewhere between 115-125 during our time in PJ2. With our attention focused on the DX contest, we didn’t have a lot of time to check 6 meters, but the few days we did check it appeared open to the south from 0000 to at least 0200.

“It was my impression that TE is a very reliable mode of communication to the south from the southern Caribbean this time of year in the early evening. I have been checking 6 meter spots for the last week, and the Brazilians and Argentineans have been having a field day beaming north in the late afternoon and early evening, with numerous contacts with KP4, TI, FM, YV, P40 and the like. PY5XX and others have also worked Spain and Portugal in Southern Europe and the Canary Islands in Africa. In fact, I think now I understand one reason why 6 meters is so popular with the Southern Brazilians and Argentineans. From PJ2, it appears there are only five countries we can work on TE -- Brazil, Argentina, Uruguay, Paraguay and Chile. I worked all but one in less than 15 minutes. Maybe four or five more countries can be worked from PJ2 via TE, if one counts islands with DXpeditions like Juan Fernandez or Trinidad. On the other hand, Brazilians and Argentineans see in their regular TE skip zone maybe 25 countries with active 6 meter populations; the countries include the northern coastal South American countries, much of Central America, the Yucatan and most of the Caribbean from Puerto Rico south.”

Thanks, John for a fascinating report!

All times listed are UTC, unless otherwise noted.

Amateur solar observer Tad Cook, K7RA, of 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 each Thursday in The ARRL Letter. You can find a guide to articles and programs concerning propagation here. Check here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.