QST de W1AW
Propagation Forecast Bulletin 13 ARLP013
>From Tad Cook, K7VVV
Seattle, WA March 27, 2001
To all radio amateurs
SB PROP ARL ARLP013
ARLP013 Propagation de K7VVV
Solar activity made a huge jump this week, with Monday's sunspot
number at 339 and solar flux at 263.7. There has been a rapid
increase in sunspots all over the visible solar disk. The most
prominent is region 9393, one of the largest sunspots observed in
recent years. Sunspots drift across the visible solar disk as the
sun goes through a 27.5 day rotation, and they have the greatest
effect on the earth when they are at the center. This sunspot has
not quite reached the center of the disk, so probably more
excitement is in store.
The sunspot number has not been anywhere near this high since last
July, in what looked like the peak for Cycle 23. From July 17-21,
2000 the sunspot numbers were 335, 343, 342, 401 and 325. During
those same five days the solar flux was 228.3, 261.9, 249.9, 252.9
and 250.9. On May 17, 2000 the solar flux was 262 and sunspot number
was 342, so by a margin of only 1.7 points, Monday of this week had
the peak solar flux value for Cycle 23.
Counting the number of spots and factoring in their area derives
sunspot numbers. Daily solar flux is a measurement of 2.8 GHz energy
read at noon daily in Penticton, British Columbia. Although this
number is more easily quantifiable, it is probably not as useful as
the sunspot number for determining the energy charging the
ionosphere, where radio waves are refracted.
The really neat thing about this peak though is that it came just
days after the spring equinox, when solar radiation is equal in the
southern and northern hemispheres, and seasonal HF conditions are at
their best. The other two peaks occurred later in the spring and in
summer. The other great thing for HF radio enthusiasts is that
geomagnetic activity has been extremely quiet. The middle latitude K
index yesterday was mostly 0 or 1, and the A index was 2. Both the
high latitude College A index and planetary A index were 6.
What often happens during a period of high sunspot count is that
there are more solar flares, and so the absorption of radio waves
increases, especially over polar paths. This week we have been very
lucky so far.
As has been mentioned in the past, the official daily solar flux is
taken at noon local time in Penticton (2000z), but there is a 1700z
and 2300z reading as well. It is not noon yet as this bulletin is
being written, but the 1700z reading this morning was 271.6. If the
noon reading is as high, it may develop that today (Tuesday) is the
solar flux peak of Cycle 23, and not yesterday.
Above all have fun on the air. I would like to hear reports of
conditions, particularly on 10 and 6 meters, which can be sent to
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