ZCZC AP21
QST de W1AW
Propagation Forecast Bulletin 21 ARLP021
From Tad Cook, K7VVV
Seattle, WA May 18, 2001
To all radio amateurs
SB PROP ARL ARLP021
ARLP021 Propagation de K7VVV
This has been a geomagnetically active week for the earth. There was only one day (last Friday) with the planetary A index in the single digits, and several days (Thursday, May 10, and the following Saturday and Sunday) stood out as stormy, with A indices above 20. The most active day was Saturday, May 12, when the planetary A index was 34 and the planetary K index was as high as 6 over two of the three-hour reporting periods. Although this is bad for HF propagation, it often produces plenty of excitement on VHF.
Friday, May 18 is expected to be unsettled to active, with a planetary A index around 20. This should settle back to 12 on Saturday and 10 for the rest of the week. The following weekend, when the CQ Worldwide WPX CW Contest is held, could be unsettled again if sunspot 9393 returns with more flares and coronal holes.
Solar flux is expected to rise over the next few days, with Friday at 150, Saturday around 155, and Sunday around 160. Flux values are expected to peak around 180 from May 24-27.
Sunspot 9393 is back for a third transit across the visible solar surface. This is unusual, although the region is much smaller than it was two months ago when it sprouted one of the biggest solar flares in recorded history.
Until recently, once an active region passed beyond view during the sun's approximately 27.5 day solar rotation relative to earth, any developments on the sun's far side were a mystery. But a new technique called helioseismic holography allows its users to peer through the sun by tracking waves of pressure that affect features on the surface.
By watching the sun's vibrating surface, helioseismologists can see regions on the other side similar to the way seismologists use earth's seismic waves to probe our planet's interior. Check http://spaceweather.com/glossary/farside.html for a good explanation of this powerful new tool.
Sunspot numbers for May 10 through 16 were 94, 96, 127, 119, 149, 146 and 125 with a mean of 122.3. 10.7 cm flux was 130.4, 136.6, 138.1, 138.9, 138.2, 142.1 and 137.8, with a mean of 137.4, and estimated planetary A indices were 28, 9, 34, 23, 12, 16 and 12 with a mean of 19.1.