SB PROP @ ARL $ARLP013 ARLP013 Propagation de K7VVV

ZCZC AP13 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 k7vvv@arrl.net. NNNN /EX

==>SOLAR UPDATE

Heliophile Tad Cook, K7VVV, Seattle, Washington, reports: This week we've seen a major geomagnetic storm, which began on Monday. The disturbance reached a peak on Tuesday, with a planetary A index of 66 and planetary K indices of 5, 6 and 7. The high-latitude college A index was 105, and the K index reached 8.

The energy released produced dramatic auroral displays. Check out the images at http://spaceweather.com/aurora/gallery_20mar01.html .

With the equinox this week, springtime HF conditions should be at a peak, when the southern and northern hemispheres each gets an equal amount of solar radiation. Average solar flux this week was 144.2 which is slightly lower than it was during this week in 1999, when it was 147.5. Last year at this time it was 207.8. So we are currently still enjoying the peak of cycle 23, but conditions are more like they were at this time two years ago.