The K7RA Solar Update
SEATTLE, WA, Jul 29, 2005--We're coming to the end of a
month of large contrasts in terms of solar activity. Around July 4 there was a
huge increase in sunspot numbers, followed by a very quiet period in which no
sunspots were seen. Although five days following mid-July were devoid of any
sunspots, our sun rotates relative to Earth--so in a little less than four
weeks that very active area of sunspots is back again in the same position.
The popular figure of 27.5 days is regarded as the period
of the sun's rotation relative to our planet, but the actual figure varies
according to which latitude of the sun we are observing. If Earth were
stationary and our observations of the sun were from a fixed point, the
rotation near the sun's equator would be about 25.6 days, and 30.9 days at 60
degrees latitude. We are most concerned with sunspots near the sun's equator,
because they are in the most "geoeffective" or Earth-affecting position
compared to those at higher latitudes.
Watch for sunspot and solar flux numbers to rise over the
next few days, peaking from August 1 until August 6 as the previous month's
spotted region returns to view. Geomagnetic indices should drop and stay low. Predicted
planetary A index for July 29 through August 2 is 15, 12, 10, 5 and 5.
Over the long term, the general direction of the cycle is
down, although variations such as the increased activity around July 4 are
occasionally observed. Looking at a smoothed prediction
for sunspot numbers over the next few years, sunspots should continue to
decline overall, and are predicted to rise again to the current level around
December 2007.
For more information concerning radio propagation and an
explanation of the numbers used in this bulletin see the ARRL Technical
Information Service Propagation
page. An archive of past bulletins
is on the ARRL Web site.
Sunspot numbers for July 21 through 27 were 0, 0, 20, 18,
23, 29 and 19, with a mean of 15.6. The 10.7 cm flux was 72.8, 73.6, 80.1,
80.2, 83.9, 86.5 and 90.6, with a mean of 81.1. Estimated planetary A indices
were 29, 13, 5, 5, 6, 6 and 17, with a mean of 11.6. Estimated mid-latitude A
indices were 19, 8, 2, 3, 3, 4 and 15, with a mean of 7.7.
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 appears in The ARRL Letter. Readers may contact
the author via e-mail.
Page last modified: 11:03 AM, 29 Jul 2005 ET
Page author: awextra@arrl.org
Copyright © 2005, American Radio Relay League, Inc. All Rights Reserved.
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