ARLP015 Propagation de K7VVV:
April 6, 2001

Propagation Forecast Bulletin 15 ARLP015
From Tad Cook, K7VVV
Seattle, WA April 6, 2001
To all radio amateurs

ARLP015 Propagation de K7VVV

This has been another week of remarkable solar activity, with Sunspot 9393 producing more excitement. Sunspot numbers peaked on March 28 and 30 at 352 and 349, and solar flux on March 27 and 28 at 273.4 and 273.5. Total visible sunspot area peaked on March 29 at 3940 millionths of the solar hemisphere. This week solar flares tossed out enough energy to overwhelm the equipment that measures 10.7 cm solar flux.

At 2300z on April 2 the flux reading was 563.1, and on April 5 the readings were 582.5 and 398.7 at 1700 and 2000z. These flare-enhanced readings would certainly be a new record far beyond any daily values reported for this solar cycle, but they are discarded because they don't reflect actual 10.7 cm energy. So for April 5, instead of a daily reading of 398.7, NOAA reported 210, probably a guess based upon declining daily readings and a more accurate 2300z reading of 207.5.

Following the new high in sunspot numbers, we have seen a number of large solar flares and resulting aurora. On April 2 the most powerful flare in at least 25 years erupted. Fortunately most of it was aimed away from earth. A few days earlier on March 31 the planetary A index soared to 155 and the planetary K index went as high as 9 during a severe geomagnetic storm. There were incredible auroral displays, seen as far south as Mexico. See an amazing gallery of aurora images, many from southern regions that very rarely see aurora, at

Since March and the first quarter of the year are both over, it is time to report some numbers for those periods. Average solar flux for March was 177.7. This is an increase, as the average daily solar flux for December through February was 173.6, 166.6 and 147.2. Average daily sunspot numbers for March were 166.7, and for December through February were 146, 143 and 131. Quarterly average solar flux for last year was 180.5, 182.9, 188.3 and 173.3.

For the first quarter of this year the average solar flux was 164.4. The average daily sunspot number for the quarter just ended was 147.3, and the quarterly sunspot averages for last year were 168.9, 190.8, 193.1 and 145. Although this quarter really ended with quite a bang, the quarterly averages for both solar flux and sunspots were lower than the same period a year earlier.

Although the really active regions have now rotated off of the visible solar disk, there are more rotating into view. Predicted solar flux for the next few days, Friday through Monday, is 210, 210, 205 and 205. The predicted planetary A index for those days is 15, 8, 8 and 10.

Someone passed along some interesting comments that Paul Harden, NA5N posted on Thursday to a discussion group for low power amateur radio. He noted that there seemed to be an HF blackout below 20 MHz caused by ionizing radiation reaching the D layer. E and F layer enhancement of the ionosphere is good for HF propagation, but D layer enhancement tends to absorb radio waves. He recommends the NOAA Space Weather Now site at , then clicking on D-region absorption to go to

For some time now W6EL's MiniProp program for propagation prediction has been unavailable. This is the program used to generate the occasional path predictions shown in this bulletin. I am extremely happy to report that W6EL has just released a new free version of his software, this time for Windows, and you can get it at It works with all recent versions of Windows, including 95, 98, ME, NT and 2000. Be sure to give this a try, and send W6EL a note of thanks. It is a great piece of software for looking at seasonal, time of day, frequency and solar activity variables and their effects on HF communications.

In closing, there was just too much to report this week, but thanks to everyone who wrote. I should also note that DL9KAC mentioned in last week's Propagation Forecast Bulletin ARLP014 is actually DL6KAC.

Sunspot numbers for March 29 through April 4 were 315, 349, 326, 320, 223, 228 and 217 with a mean of 282.6. 10.7 cm flux was 261.7, 256.8, 245.6, 257.5, 228, 223.1 and 204.8, with a mean of 239.6, and estimated planetary A indices were 22, 10, 155, 30, 20, 5 and 15 with a mean of 36.7.