The K7VVV Solar Update

SEATTLE, WA, Apr 19, 2002--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 six, which is very high. The high latitude College A index was 73, and the College K index reached 7.

On April 15 at 0400 UTC a full halo coronal mass ejection blasted away from the sun. At 1100 UTC 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 US 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 0052 UTC. This was with only a three-element Yagi at 30 feet.

Sunspot numbers for April 11 through 17 were 235, 263, 257, 236, 243, 172 and 137, with a mean of 220.4. The 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. Estimated planetary A indices were 13, 13, 14, 13, 7, 10 and 41 with a mean of 15.9.

Amateur solar observer Tad Cook, K7VVV Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday, and an abbreviated version also appears in The ARRL Letter. Readers may contact the author via k7vvv@arrl.net.

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