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The K7RA Solar Update

09/26/2008

This week saw the appearance of another sunspot -- a new Solar Cycle 24 spot -- larger and lasting a little longer than last week's Solar Cycle 23 sunspot. It appeared for two days, September 22 and 23, with sunspot numbers of 18 and 16.

Geomagnetic activity is very quiet; on September 25, the K index was 0 for a good part of the day. This was true for the mid-latitude index, planetary and the college K index in Alaska. The three corresponding A indices for the day were 4, 1 and 1, respectively. This is especially nice for the lower part of the HF spectrum, such as our 160 and 80 meter bands, and something we don't see during periods of higher sunspot activity.

Geophysical Institute Prague predicts quiet conditions September 26-29, unsettled September 30, active October 1 and unsettled conditions on October 2. Sunspot numbers for September 18-24 were 0, 0, 0, 0, 18 16, and 0 with a mean of 4.9. The 10.7 cm flux was 67.2, 67.9, 67.8, 67.9, 69.1, 69.4 and 68.4 with a mean of 68.2. The Estimated planetary A indices were 9, 5, 3, 2, 4, 3 and 4 with a mean of 4.3, and the estimated mid-latitude A indices were 5, 3, 1, 1, 2, 2 and 1 with a mean of 2.1.

Last week's bulletin mentioned an announcement coming on Tuesday this week from NASA. It concerned data from the Ulysses spacecraft, indicating solar wind pressure is declining. The speed of solar wind hasn't changed much, but the density and temperature are lower. The Ulysses craft orbits the Sun over a six year period, during which it flies over both the Sun's south and north poles. The average solar wind pressure measured from February 1992-February 1998 declined over the following decade, and the pressure during the February 2002 to February 2008 pass was about 20 percent lower.

In addition, the solar magnetic field dropped more than 30 percent over the same period. Because the data has been collected over such a short time, there isn't much historical context for these readings. What does this indicate for radio propagation? Unknown, but perhaps this shows overall slowing of solar activity.

Last week's bulletin also said that the predicted planetary A index for September 30-October 2 was 8, 30 and 8. This prediction has moderated somewhat; currently, the expected values are 8, 20 and 10.

Scott Bidstrup, WA7UZO, who lives in Costa Rica, sent an interesting article about noctilucent clouds as a possible medium for UHF propagation. According to the article in Science Daily, the clouds contain ice coated with sodium and iron from micro-meteors and sit at about 53 miles (85 km) altitude, mostly between 50-70 degrees latitude and sometimes as far south (or north, in the southern hemisphere) as 40 degrees latitude or less.

The clouds are highly reflective of radar signals, and instead of diffraction as we see in ionospheric propagation, ripples in the clouds seem to reflect in unison, reinforcing each other.

Noctilucent clouds are sometimes visible at night because their altitude is so high that they reflect sunlight into areas of darkness. They are also known as polar mesospheric clouds, and appear most often at twilight during the summer. Look here for images of noctilucent clouds.

John Becker, K9MM, of Prospect Heights, Illinois, wrote about some unusual 30 meter propagation. On September 23 at 2006 UTC, he worked H40MY in Solomon Islands on 30 meters with solid copy. John used an inverted V and thinks perhaps propagation was via long path, because the short path was entirely in daylight. Short path propagation would be best between 0600-1400 UTC.

Cesar, PY2YP, sent in a reference to his Web site that describes an interesting method of propagation prediction based on cracking large pileups. Instead of just calculating the signal strength over time between you and your target, it also factors in signal strength to the target station from various pileup generators, or sources of interference. It determines when you are likely to be louder toward the DXpedition than other regions. Check it out on Cesar's Web site; click on "QSO Window Tutorial" from the list onm the left hand side of the page.

Amateur solar observer Tad Cook, K7RA, of 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. Check here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.



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