The K7RA Solar Update


Increasing sunspot activity continues. A glance at the image from NASA's STEREO mission shows a string of active regions in the Sun's northern hemisphere, both visible and over the horizon on the far side. The high sunspot number for the week was 71 on February 8; the average for the week was 43.3. We haven't reported a weekly average that high since the week of March 27-April 4 in 2008, when it was 43.6. The daily sunspot number hasn't been as high as 71 since May 28, 2006 when it was 78. The earlier reading that reached that level or more was 105 on April 6, 2006.

On February 8 -- when the daily sunspot number was 71 -- the total area covered by sunspot activity was 460 millionths of a solar hemisphere. That measure hasn't been that high since the same earlier week in 2008 that had a high sunspot number average. The dates were March 26-27, 2008 when the area of sunspots was 520 and 510. You can find continuous records of these old indices going back through 1994 here.

Sunspot numbers for February 4-10 were 11, 22, 30, 51, 71, 63 and 55, with a mean of 43.3. The 10.7 cm flux was 73.9, 77.8, 87.5, 90.3, 93.7, 91.4 and 91.3, with a mean of 86.6. The estimated planetary A indices were 2, 3, 4, 3, 3, 3 and 3, with a mean of 3. The estimated mid-latitude A indices were 2, 0, 2, 2, 3, 1 and 1, with a mean of 1.6. The latest forecast has the solar flux index for today, February 12 at 90, followed by 92 on February 13, 94 on February 14-16 and 93 on February 17-18. The predicted planetary A index for February 12-18 is 10, 8, 8, 7, 8, 8 and 5. Geophysical Institute Prague sees unsettled conditions February 12-13, unsettled to active February 14, unsettled February 15, quiet to unsettled February 16 and quiet February 17-18.

A number of people have inquired about short vs long skip on 75/80 meters, wondering why short skip is often non-existent, but long skip is enhanced. Dennis Carlson, K9ZMI, of Arlington Heights, Illinois, provides an explanation: "As I understand it, the effect we are seeing is that the F-layer ionization is weak because of low sunspot activity. A weakly ionized layer has a low index of refraction (a term used in optics) which impacts the amount of bending of the HF radio wave impinging on it. Low index of refraction equals not much bending. So an HF radio wave leaving an antenna is typically headed toward outer space but is bent back (refracted) towards Earth when it reaches the ionized layers above Earth. The amount of bending depends on the index of refraction and, for a given index of refraction, the angle of impingement determines if the radio wave will return to Earth or not. HF radio signals impinging on the weakly ionized layer at a high angle (necessary for short skip communications between stations close to each other) are not refracted enough to be 'turned back' to Earth and they simply radiate into space. Signals impinging on the weakly ionized layer at a low angle are refracted enough to be 'turned back' to earth and they appear at a large distance from the signal's origin, which is long skip."

Thank you, Dennis. If we look at ionosonde data for Boulder, Colorado, a glance at the foF2 column is instructive. This is the highest frequency that bounces back a signal from the ionosphere directly above, with a signal beaming straight up. For reliable short-skip communications on 75 meters, we need the foF2 to be at least 4 MHz. It may be different by the time you see it, but starting at 0000 UTC on February 11, I see the foF2 dipping below 4 MHz from 0115-1115 UTC, 1145-1330 UTC and on February 12 0115-0515 UTC, 0600-0615 UTC, 0700-0715 UTC and so on. On February 12, the approximate sunrise at the ionosonde is at 1402 UTC and sunset at 0028 UTC. It appears that roughly after sunset until sunrise, possibly there isn't enough sunlight to support short skip on 75 meters.

On Thursday, Bob Marston, K6TR, sent this: "Today, Feb 11, NASA successfully launched the Solar Dynamics Observatory at 10:23 AM EST from Launch Complex 41 at Cape Canaveral Air Force Station in Florida. After completing its second burn 90 minutes after liftoff, the Atlas Centaur booster released SDO in a 1900×21,000 mile elliptical geostationary transfer orbit. Through a series of burns over the next three weeks, SDO's propulsion system will circularize the orbit. First light from the observatory can be expected in 60 days; full calibration of the satellite will be completed in early July. Carried on board SDO is the Extreme Ultraviolet Variability Experiment -- which will render data of importance to ham radio operators interested in HF Propagation. The EVE will sample solar radiation in the 304 angstrom range that composes half of all radiation that goes into ionizing the F layer of the ionosphere. The 304A number represents a tighter real-time correlation to F layer ionization that the smooth sunspot number (SSN) or the 2800 MHz solar flux number." According to news reports, the scheduled launch on Tuesday was delayed due to high winds. You can find more information on SDO here or on their YouTube channel.

Paul Graziani, W5ZK, of Little Rock, Arkansas, sent an article from NASA about the SDO "Variable Sun Mission." D. Moore, who regularly sends articles of interest, referred us here for another article on SDO.

Jon Jones, N0JK, of Wichita, Kansas is still sending us 6 meter reports. On February 3, he reported a great deal of sporadic-E activity to Mexico and Central America from the Western US. He noted that sporadic-E activity is unusual in February, and "the openings January 31-February 2 were intense, long lasting, strong and favored northern tier stations such as VE1, VE2, VE3, VE4, W1, W2, W3 and W8, W9 and W0. It was more like mid-summer. Usually, February E-skip favors stations along the Gulf Coast, Arizona and California to XE, TI, YN, KP4 and more."

He sent us a bar chart showing that sporadic-E activity is lowest in March and highest in May, June and July, with June at the peak. On the evening of February 5 (February 6 UTC), he reported a lot of 6 meter E-skip activity from Southern California and Arizona to Central America and Mexico. He sent logs showing K7JA, KS7S, K6QXY, AJ4F and K6LPO all getting in on the fun. Yesterday, February 11, he sent an e-mail noting more 6 meter E-skip, noting that there have been E-skip openings on 6 meters every day since January 31.

Juan Carlos, CO8TW, of Santiago, Cuba says he has a new Web page that aggregates propagation related data from a number of sources. Click on the "Go back to home page" link to learn interesting things about ham radio in Cuba.

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.