QST de W1AW
Propagation Forecast Bulletin 25 ARLP025
From Tad Cook, K7RA
Seattle, WA June 20, 2003
To all radio amateurs
SB PROP ARL ARLP025
ARLP025 Propagation de K7RA
Low sunspot numbers and geomagnetic disturbances in the over-the-hill portion of the solar cycle continue. There are enough sunspots for some good HF propagation, but we are about three years past the cycle peak and about three and a half years ahead of the next sunspot minimum. Complicating the situation is continued high solar wind and flares, causing constant disturbance to geomagnetic conditions. HF operators generally want stable geomagnetic indices, such as a K index at 3 or below and a daily A index of 10 or less.
A chart in the recent NOAA Preliminary Report and Forecast of Solar Geophysical Data at http://www.sec.noaa.gov/weekly/pdf/prf1450.pdf shows the enhanced geomagnetic activity following the peak of a solar cycle. Go to the last page of the report, and look at the bar graphs for severe storm conditions, expressed as a planetary A index over 100.
Note that for a few years after high solar activity the geomagnetic indices are higher. Another report from last week at http://www.sec.noaa.gov/weekly/pdf/prf1449.pdf projects our position in the current cycle. Look at the last page, and see a rising historical planetary A index. Look at the previous few pages, and see the smoothed sunspot and solar flux projections.
The next minimum appears sometime around the end of 2006. By the way, this publication is full of interesting information and appears weekly at http://www.sec.noaa.gov/weekly/index.html.
William Hartman, N6FB forwarded a question from the eHam.net forum about the relation between A and K indices, as well as a few other questions. The K index is a measure of geomagnetic stability at various magnetometers around the globe. During periods of activity, the higher latitudes tend to have higher K indices. For mid-latitude K values, an index of 3 is normal. Below 3 is nice and quiet, and above is disturbed. Each point in the K index, which is published every three hours, represents a big change. It is a non-linear system.
The A index is published daily, and is made up of the eight K indices over 24 hours. It is a linear scale, so a one point change doesn't represent a big jump in activity. For instance, if you had a constant K index of 2 for 24 hours this would produce an A index of 7. A constant K index of 3 is equal to an A of 15, and K of 4 equals 27. The K usually changes every three hours, so the A is somewhere in between the values shown here. A web page that shows the relationship is at http://www.ngdc.noaa.gov/stp/GEOMAG/kp_ap.html.
You can see recent mid-latitude, high and planetary A and K indices at http://www.sec.noaa.gov/ftpdir/indices/DGD.txt. Note that on June 17 and 18, 2003 we had a planetary A index of 50 and 54, which is very high.
June 17 and 18 activity was significant, and Al Olcott, K7ICW sent an email commenting that the recent sporadic E skip on 144 and 222 MHz was of historic importance. He is in Las Vegas, and on June 17th on 222 MHz, he worked K7MAC in Idaho. K7MAC was S7, and on 144 MHz he was S9 into Nevada, a 544-mile path.
The June 17 and 18 numbers were the result of yet another robust interplanetary shock wave, which swept over the earth around 0500z on June 18. It was probably from a coronal mass ejection hurled from sunspot 365 on June 15, the day that this sunspot reappeared. In May that same spot released two X-class solar flares, big ones.
Mark Williams, KF6YU wrote about an unusual experience on June 14 around 0000z. He was vacationing in Payson, Arizona and an AM broadcast station he was listening to in his truck abruptly disappeared. He switched to FM to listen to a Phoenix station, and instead heard one in Sioux City, Iowa on that frequency. When he got back to his cabin, he listened to dead air on HF, and the whole phenomenon was over in about 30 minutes.
Someone had a question about what Carl Luetzelschwab, K9LA meant when he referred to IMF in an email quoted in last week's bulletin. IMF in this context doesn't refer to global banking or third-world debt, but the Interplanetary Magnetic Field. When a strong solar wind or interplanetary shock wave from the sun blasts earth, the IMF tends to point south. This has been covered several times in this bulletin over the past year, but now may be a good time to review the IMF and its significance at http://spaceweather.com/glossary/imf.html.
In addition, in last week's bulletin we hoped to come up with some images showing the effects on the spectrograph at Project JOVE during an x-ray event on June 9. Jim Sky, KH6SKY sent the link, http://radiosky.com/wccro_spec_030609.html. The strip charts were produced with Radio-Skypipe software. Check http://radiosky.com/skypipeishere.html for information.
Back to recent indices as well as a projection for the next few days, we had average sunspot numbers drop nearly 37 points from last week to 112.7 this week. Solar flux was also down. Not surprisingly given the conditions and all the reports, the average planetary A index increased from 21 to 30. Space weather was remarkably mild on Thursday, June 19 with mid latitude and planetary K indices down to 2 or 3. However, the forecast shows more of the same enhanced activity over the next few days, with a planetary A index of 25, 25, 20 and 20 for June 20-23. Solar flux should remain around 125 on those days. On June 20 we should enter a solar wind stream flowing from a coronal hole, which should cause those high A indices.
Sunspot numbers for June 12 through 18 were 168, 149, 91, 111, 91, 80, and 99, with a mean of 112.7. 10.7 cm flux was 163.5, 151, 133.5, 128.7, 122.6, 121.9, and 120.4, with a mean of 134.5. Estimated planetary A indices were 11, 11, 32, 20, 32, 50, and 54, with a mean of 30.