This week’s bulletin was written by Carl Luetzelschwab, K9LA. Carl is filling in for Tad Cook, K7RA.

I bet you have this memorized: "Solar activity was very low throughout the reporting period, and geomagnetic field activity was at quiet levels during most of the reporting period." Enough said? The first sunspot region of Solar Cycle 24 occurred on January 4, 2008. Since then, though, Solar Cycle 24 spots have been few and far between.

A good summary of this solar minimum can be made in two statements. The first statement is that the duration of this solar minimum is unusual compared to the other solar minimums in our lifetime. That's because from the minimum between Solar Cycle 17 and 18 onward, solar minimums have been roughly two years. Thus we've only been exposed to "short" solar minimum periods. A look at all history shows a different story and brings us to the second statement. This solar minimum, which is going on three years now, is pretty much average in duration compared to all history. What this all says is the Sun has been highly variable throughout recorded history.

Sunspot numbers for June 11-17 were 0, 12, 0, 0, 0 0, and 11 with a mean of 3.3. The 10.7 cm flux was 69.3, 69, 68.2, 68.1, 67.4, 68.3 and 67.8 with a mean of 68.3. The estimated planetary A indices were 3, 2, 4, 6, 4, 3 and 3 with a mean of 3.6. The estimated mid-latitude A indices were 2, 1, 3, 4, 4, 4 and 1 with a mean of 2.7.

Cycle 24 Predictions

If you dig through the technical literature, you'll discover that there are more than 50 predictions for Solar Cycle 24. They range from a low smoothed sunspot number of 40 to a high of 185. Why are there so many predictions? That's a simple question to answer -- solar scientists do not fully understand the process that generates sunspots, and thus many different methods have been used to make a prediction.

Does this mean they're guessing and should be admonished for not being correct? I personally don't think so. What we're seeing is the scientific process in use. A prediction is made using a certain method, and Solar Cycle 24's progress -- or lack of progress -- allows scientists a means to test their theory. That's how science works when we don't understand something.

Will we ever figure this out? I can't answer that question, but I recently read an interesting NASA Headline News story saying that scientists announced "a jet stream deep inside the Sun is migrating slower than usual through the star's interior, giving rise to the lack of sunspots." Perhaps this will be an important clue to help our understanding of the sunspot process.

Noctilucent Clouds Return

As reported at spaceweather.com on May 31, the first noctilucent clouds (NLC) of the 2009 season were sighted over Russia on May 27. NLCs typically appear about 20 days prior to the summer solstice, increase quickly to a high summer level and then disappear about 50 days after the summer solstice. These clouds are mostly a high latitude phenomenon, and are believed to be composed of ice crystals.

VHF radars see very strong echoes from these clouds, and since they are at mesospheric heights (80 to 90 km), they are also known as polar mesosphere summer echoes (PMSE). These clouds are hypothesized by Han Higasa, JE1BMJ, and others to be responsible for 6 meter propagation across high latitudes (for example, from the East Coast of North America to Japan) during the northern hemisphere summer. This mode of propagation has been dubbed Summer Solstice Short-path Propagation (SSSP). Check out page 34 of the February 2009 issue of WorldRadio Online for a general discussion of PMSE and SSSP and for references in the technical literature. To reiterate, SSSP is still just a theory, but the occurrences of QSOs appear to match the occurrence pattern of PMSE.

Getting Ready for Glorioso

Beginning on July 9 and continuing through July 28, a French team expects to activate this extremely rare DXCC entity (it's in the Top 5 in the Most Wanted Survey as listed in the January/February 2009 issue of The DX Magazine).

Glorioso is located in the Indian Ocean near the northern tip of Madagascar and enjoys higher-than-usual MUFs (maximum usable frequencies) even at solar minimum, due to the robust equatorial ionosphere. Unfortunately the North American end of the path will suffer from low MUFs due to a combination of solar minimum and a summer month. The result of this is that 15, 12 and 10 meters will likely not produce many QSOs between Glorioso and North America. My recommendation is to concentrate your efforts on 40, 30, 20 and 17 meters. And if you need Glorioso for an all-time new one for DXCC, be sure to work this DXpedition -- it will probably be quite a while until it is again activated.

I was saddened to read that Jim Tabor, KU5S, passed away on May 27. Jim was the driving force behind Kangaroo Tabor Software, which offered propagation prediction programs such as CapMAN and WinCAP Wizard, programs to help monitor the NCDXF/IARU beacons and several other propagation-related packages. Jim also contributed propagation software to the CD-ROM bundled with The ARRL Antenna Book. I personally enjoyed many e-mail exchanges and several QSOs with Jim, talking about various propagation and ionospheric issues.

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.