High-frequency Propagation This Month
Sunspot Cycle 24 has been quite tame compared with recent cycles. Some are speculating that we’ve already seen the peak of this cycle—but time will tell. How alive can the higher frequencies be with long-distance propagation? It is always a surprise to the casual Amateur Radio Operator and SWLer when they get on a band like ten meters during the solar minimum, and discover that there is still some life on the band, beyond Short-Skip distances. This can be especially true during periods when massive sunspots occur and raise the daily 10.7-cm flux levels enough to wake up the higher frequencies. However, the low solar activity of recent months just does not support world-wide Dxing on the highest HF bands for any significant length of days. The lower HF bands can become real players, though, as veteran HF operators know.
We are starting to approach the end of the winter season. The period of darkness is growing shorter, causing a rise of the average daily maximum usable frequency (MUF) on any given radio propagation path that traverses the ionosphere in the Northern Hemisphere. That’s helpful in overcoming the increasing geomagnetic activity expected. Additionally, noise levels are still low, so reliable DX is possible. The solar activity is finally high enough to provide HF ionospheric propagation on higher frequencies (even some low-VHF F-region propagation has been observed since late 2011). General conditions are expected to be good to excellent for HF propagation throughout February.
Specifically, during the first three months of the year the earth is at perigee with the sun. This causes long winter nights, which in turn allows the ions of lower layers to drift upward and add to the F2 region. The F2 region contains the maximum ion density (foF2), which usually defines the maximum usable frequency (MUF) for DX paths.
Throughout these winter months, the foF2 increases slowly day-by-day until it reaches the highest monthly average of the year sometime during this quarter.
On the shortwave bands above 22 meters, expect paths to open shortly after sunrise, and will remain open until early to late evening. Morning and evening DX openings between some areas in the Northern Hemisphere on these bands are very short, because the band in question closes on one end of the path before it opens on the opposite end.
Paths on 31 through 22 meters remain in their seasonal peak much like in January, but with longer openings. Continue to look for great openings between North America and Europe in the morning and between North America and Asia during the late afternoon hours. Twenty-two meters will often be the best daytime DX band, with 31 and 25 running a close second.
Ninety through 41 meters will be useful almost 24 hours a day. Daytime conditions will resemble those of 25 meters, but skip and signal strength may decrease during midday on days with high solar flux values. Nighttime will be good except after days of very high MUF conditions. Generally, the usable distance is expected to be somewhat greater on the higher of these bands than on 90. DX activity tends to increase later in the evening toward midnight. Look for Africa and South Pacific (Australia, Papua New Guinea, and so on) on 90 through 60 meters throughout the night. On 41, 49 and 60 meters, long path DX is possible along the gray line.
The 120-meter band continues to remain stable, with very low noise levels. Throughout the winter season, high noise may occur during regional snowstorms. The band opens just before sunset and lasts until the sun comes up on the path of interest. Except for daytime short-skip signal strengths, high solar activity has little impact. Continue to look for Europe and Africa around sunset until the middle of the night, and then Asia, the Pacific, and the South Pacific as morning approaches.
Signals below 120 meters will remain strong and exciting, except during times of regional storms and high geomagnetic activity. Medium Wave DX is still quite hot throughout February.
Trans-equatorial (TE) scatter propagation tends to increase during the equinoctial period and some 6-meter openings may be possible between 7 and 10 PM local time. The best bet for such openings is between the southern tier states and South America for paths approximately at right angles to the equator. An occasional TE opening may also be possible on 2 meters. Unlike F2-layer or sporadic-E openings on 6 meters, TE openings are characterized by very weak signals with considerable flutter fading.
If you use Twitter.com – you can follow @hfradiospacewx for hourly updates that include the K index numbers (and, follow this columnist – @nw7us). You can also check the numbers at < http://SunSpotWatch.com >.
CURRENT SOLAR CYCLE PROGRESS
The Royal Observatory of Belgium, the world’s official keeper of sunspot records, reports a monthly mean sunspot number of 90.3 for December, 2013, up from November’s 77.6 and from October’s 85.6. The low for the month was 65 on December 7. The high of 136 occurred on December 10. The mean value for December results in a 12-month running smoothed sunspot number of 62.6 centered on June 2013. Following the curve of the 13-month running smoothed values, a smoothed sunspot level of 79 is expected for February 2014, plus or minus 14 points.
Canada's Dominion Radio Astrophysical Observatory at Penticton, British Columbia reports a 10.7-cm observed monthly mean solar flux of 147.7 for December, 2013, about the same as November’s 148.4. This indicates a clear resurgence of solar activity. This provided a lot of great DX and activity even on the Ten-meter band. The twelve-month smoothed 10.7-cm flux centered on June 2013 is 120.9, up from May’s 118.1. A smoothed 10.7-cm solar flux of about 134 is predicted for February 2014.
The geomagnetic activity as measured by the planetary-A index (Ap) for December 2013 is 5. The twelve-month smoothed Ap index centered on June 2013 is a steady 7.1. Geomagnetic activity should be much the same as we have had during January. Refer to the Last Minute Forecast for the outlook on what days that this might occur (remember that you can get an up-to-the-day Last Minute Forecast at < http://SunSpotWatch.com > on the main page).
I'd like to hear from you
I welcome your thoughts, questions, and experiences regarding this fascinating science of propagation. You may e-mail me, write me a letter, or catch me on the HF Amateur bands. On Twitter, please follow @NW7US (and if you wish to have an hourly automated update on space weather conditions and other radio propagation-related updates, follow @hfradiospacewx). I invite you to visit my online propagation resource at < http://sunspotwatch.com/ >, where you can get the latest space data, forecasts, and more, all in an organized manner. If you are on Facebook, check out < http://www.facebook.com/spacewx.hfradio > and < http://www.facebook.com/NW7US >.
Until next month,
73, Tomas, NW7US
PO Box 27654
Omaha, NE 68127