The K7RA Solar Update
SEATTLE, WA, May 21, 2004--Solar flux values and sunspot
numbers moved higher over the past week. Average daily sunspot numbers rose
nearly 65 points to 113.6. Average solar flux rose more than 18 points. The
sunspot number reached a peak of 148 and 147 on Sunday and Monday, May 16-17. This
was due to the growth of Sunspot 609, which expanded dramatically along with a
host of other spots. A medium-sized sunspot group is on the sun's far side, as
detected by helioseismic holography. There were some unsettled conditions last
Thursday, May 13, but the rest of the week was quiet, with low K and A indices.
We are currently within a weak stream of solar wind from a
coronal hole, so some resulting geomagnetic activity is possible. The predicted
planetary A index for May 21-24 is 15, 15, 12 and 10. Solar flux should stay
around 100 during the next week.
We are moving into late spring, with the longest day of
the year just one month away. As the days become longer, we'll notice worldwide
openings on 15 meters are not as common as they were earlier in spring. Worldwide
40 meter openings will come later in the evening, as the hour of sunset
advances. Users of lower frequencies, which depend on darkness for long
distance communication, may notice shorter duration openings through the night
because there are less hours of darkness. Seasonal noise levels should begin to
rise as well.
Solar numbers aren't holding up too badly, considering
where we are in the current cycle. Note that the average sunspot number this
week at 113.6 is higher than the same week a year ago, when it was only 83.6. However,
two years ago it was 160.3 and a year prior to that it was 122.3. There are
still good openings in store for us, but the optimal frequencies will be lower,
and, except for some sporadic-E skip, we won't see the exciting 10 meter
propagation we did a few years back.
Sunspot numbers for May 13 through 19 were 107, 98, 117,
148, 147, 91 and 87, with a mean of 113.6. The 10.7 cm flux was 100.8, 109.6,
115.3, 118.3, 111.1, 107.8 and 108.8, with a mean of 110.2. Estimated planetary
A indices were 13, 8, 9, 4, 5, 4 and 6, with a mean of 7. Estimated
mid-latitude A indices were 17, 4, 7, 4, 3, 4 and 6, with a mean of 6.4.
Amateur
solar observer Tad Cook, K7RA, 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 k7ra@arrl.net.
Page last modified: 10:12 AM, 21 May 2004 ET
Page author: awextra@arrl.org
Copyright © 2004, American Radio Relay League, Inc. All Rights Reserved.
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