ZCZC AP16
QST de W1AW
Propagation Forecast Bulletin 16 ARLP016
From Tad Cook, K7VVV
Seattle, WA April 19, 2002
To all radio amateurs
SB PROP ARL ARLP016
ARLP016 Propagation de K7VVV
Average daily sunspot number was up slightly and the average solar flux was down a couple of points this week, but the big news was the high geomagnetic activity. On Wednesday the planetary A index was 41, and K indices over several reporting periods were 6, which is very high. The high latitude College A index was 73 and the College K index reached 7.
On April 15 at 0400z a full halo coronal mass ejection blasted away from the sun. At 1100z on April 17 energy from that coronal mass ejection struck earth's magnetosphere, triggering a geomagnetic storm. Several hours earlier another coronal mass ejection left the sun, and effects from it may be felt on Friday or Saturday.
On Thursday the prediction from the U.S. Air Force was for a planetary A index of 40 on Friday, 50 on Saturday, and 20 on Sunday. It also shows solar flux bottoming-out for the short term around 170 on Sunday or Monday, then rising above 200 after April 29.
With a predicted geomagnetic storm this weekend expect particularly bad propagation over polar paths, conditions worsening for higher latitudes, and some transequatorial propagation, but only because that may be the only HF propagation available. Sometimes it is assumed that transequatorial propagation (signals crossing the equator) is enhanced during geomagnetic storms, but actually these signals at times are the only audible ones.
There was more 6-meter news, this time from W4NTI. From East Central Alabama (EM73) he worked Chile and Argentina last Friday evening from 0019 to 0052z. This was with only a three-element Yagi at 30 feet.
Last week's bulletin presented a problem for users of WA4TTK's solar data plotting utility. This program grabs the data in the paragraph below and adds it to a database for charting. Unfortunately if you look at the second sentence in the first paragraph of last week's bulletin, it contains a string of words identical to one found at the end of every bulletin. I can't spell it out here, or I would cause the same problem all over again. You can get the plotting utility to ignore that error if you take out that line. Or you can use the ftp function in the program to download the data from ARRL.
Sunspot numbers for April 11 through 17 were 235, 263, 257, 236, 243, 172 and 137 with a mean of 220.4. 10.7 cm flux was 197.4, 211.9, 226, 210.3, 203.3, 195.7 and 193.5, with a mean of 205.4, and estimated planetary A indices were 13, 13, 14, 13, 7, 10 and 41 with a mean of 15.9.