ARRL

News

The K7RA Solar Update

03/28/2008

It is exciting to see heightened solar activity one week into spring. Currently, three sunspots are visible: 987, 988 and 989. The consensus says that all seem to be old Solar Cycle 23 spots. But with the three sunspot groups so close to the Sun's equator, it is hard to tell for certain. We know that Cycle 24 spots should have magnetic polarity opposing the magnetic signature of Cycle 23 sunspots, but this is also true for sunspots below the equator relative to sunspots above.

Average sunspot numbers for the reporting week (Thursday through Wednesday) rose more than 18 points from the previous week, to 23.4. The average daily solar flux was up nearly six points to 75.4. The average geomagnetic indicators were unchanged, but this is because they fell from the start of last week and rose this week. Sunspot numbers for March 20 through 26 were 0, 0, 0, 14, 35, 52 and 63 with a mean of 23.4. The 10.7 cm flux was 68.4, 68.2, 69.6, 72, 79.4, 88.6, and 81.6 with a mean of 75.4. Estimated planetary A indices were 8, 5, 5, 8, 4, 4 and 27 with a mean of 8.7. Estimated mid-latitude A indices were 7, 4, 4, 7, 2, 3 and 16 with a mean of 6.1.

The short term forecast is for sunspot activity around where it has been for the past few days, possibly extending to the end of the first week in April. Predicted planetary A index for March 28-April 7 is 15, 10, 10, 5, 8, 5, 5, 15, 25, 15 and 10. Geophysical Institute Prague predicts unsettled to active conditions for March 28, unsettled March 29-30, quiet to unsettled March 31 through April 1 and quiet conditions April 2-3.

An M2 class solar flare erupted from sunspot 989 on March 25, but it was not Earth-directed. Even so, it stimulated geomagnetic activity over the following two days. The mid-latitude K index peaked at 5, early (UTC) on March 27, Wednesday evening in North America. The high latitude College K index (Fairbanks, Alaska) peaked earlier from 0900-1500 UTC on March 26 at a level of 6. This was 1-7AM Alaska Daylight Time on Wednesday.

Expect improved conditions for the CQ World Wide WPX SSB Contest this weekend.

With the VHF discussions in this bulletin over the past few weeks, John Adams, K4JYX, of Port Orange, Florida, wanted to remind us about ducting. About 10 years ago, John said he was on 2 meter FM in Daytona Beach when he tuned across a full-quieting signal from a repeater he sensed couldn't be local. The conversation he monitored mentioned downtown Cleveland, and he was trying to think of a Cleveland, other than the one in Ohio that he might be hearing, but Cleveland, Tennessee was too far away. John broke in, mentioned he was in Daytona; the other operators thought he was in Dayton. John was running 25 W into a vertical, and the conversation continued with strong signals. John writes, "We carried on for about 35 minutes and suddenly they disappeared, never to be heard from again. I checked The Weather Channel and a front had just passed -- a front that had extended up through Cleveland, Ohio. The signals apparently entered the temperature inverted front and were ducted as if in a physical duct, the 1600 miles or so between us. Freak QSOs are fun!"

Jon Jones, N0JK, responded to JE1BMJ's comments attributing long-distance 6 meter propagation to Polar Mesosphere Summer Echo. Jon published a paper in the 2007 Central States VHF Society Proceedings analyzing JA to USA and Europe multi-hop openings in 2006. He said the propagation was "multi-hop sporadic E. Some of the E-skip hops may have been 'E-skip cloud to E-skip cloud' in addition to 'ground to E-skip cloud to ground.' The path loss may have been reduced by E-skip hops over salt water. The footprints via multi-hop E-skip can 'focus' at times to relatively small areas."

Some 10 meter reports arrived this week: Joaquin Montoya, EA2CCG, reports from Northern Spain that on Friday, March 21, 10 meter signals from South America were quite strong. He mentioned Argentina and Brazil coming in at S7-9; a friend of his worked a Brazilian with just an antenna on his balcony. Terry Oldham, KH6MT, of Grand Island, Florida, notes that on Thursday, March 27, he heard Hawaii stations on 10 meters.

Carl Luetzelschwab, K9LA, mentioned that in our last bulletin the claim was made that at the equinox, "all of the earth is receiving a maximum amount of solar radiation, the same in both southern and northern hemispheres." He pointed out that this is not really the case, as the Sun's output is constant for all practical purposes. Carl wrote, "At the equinoxes, both hemispheres are illuminated equally, i.e., the angles of incidence of solar radiation on the atmosphere in both hemispheres are similar. In the northern hemisphere summer, the angle of incidence is closest to perpendicular, providing the highest residual nighttime MUFs. One would thus think that summer daytime MUFs would also be higher, but another process comes into play to alter that -- the ratio of atomic oxygen (important for electron production) to molecular oxygen. Molecular nitrogen (important for electron loss) is higher in winter than in summer, resulting in higher daytime MUFs in the winter. This is the so-called F2 region winter anomaly."

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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