Monday, February 3, 2014

February: NW7US's SWL-Ham Radio Prop Outlook


February 2014

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.

VHF Conditions

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 – 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 < >.


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 < > 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 < >, where you can get the latest space data, forecasts, and more, all in an organized manner.  If you are on Facebook, check out < > and < >. 

Until next month,

73, Tomas, NW7US
PO Box 27654
Omaha, NE 68127


February 2014 Practical Propagation

 The Need for a Smoothed Solar Index – Characterizing a Solar Cycle

This is Part I of K9LA's series on the value of determining a smoothed solar index. It appeared in the final edition of WorldRadio Online magazine, January 2013. - KI6SN


            Sunspots have been observed for more than 2000 years. The invention of the telescope in the early 1600s allowed permanent records of sunspot activity to be made. Around the middle of the 18th century European astronomers began keeping records on a regular basis. From these records scientists put together the familiar sunspot cycle plot that started with Cycle 1 in 1755, and continues with the present Cycle 24.
            The raw data is a daily sunspot number. The data in the early cycles is sometimes sparse but by 1850, around the peak of Cycle 9, the data was very reliable.
            (BACKGROUND:  My “Propagation” column in the November 2011 edition of WorldRadio Online, Photo A, discusses the possibility of missing an early solar cycle due to insufficient data. The gaps were shown in Figure 1 of that column. – K9LA.)
            After World War II – 1947, to be exact – we began measuring 10.7 cm solar flux. The 10.7 cm solar flux is objective: it’s a measurement, assuming a calibrated set-up. Visually counting sunspots, on the other hand, is subjective. In other words, human interpretation is required. Just like sunspots, the raw data is a daily 10.7 cm solar flux value.

Modern Methodology
            So why do we need anything more than the daily sunspot number or daily 10.7 cm solar flux? There are two reasons.
  • The first has to do with characterizing a solar cycle, which I’ll address in this month’s column.
  • The second has to do with propagation predictions, which I’ll address in next month’s column.
            Accompanying this column, Figure 1 shows Cycle 23 in terms of the daily sunspot number. The data is very spiky, which simply says the daily sunspot number – and daily 10.7 cm solar flux – are very dynamic. With respect to the figure, three questions to ask are:
  • When did Cycle 23 start?
  • When and how big was the maximum?
  • When did Cycle 23 end?

Figure 1 – Cycle 23 daily sunspot numbers

When, What and Why?
            As for the start of Cycle 23, it was likely sometime in 1996. The spiky data precludes pinning this down to a specific month.
            As for the maximum of Cycle 23, it kind of looks like there might have been two peaks – one around the middle of 2000 when the sunspot number was almost 250 and another in early 2001 when the sunspot number was around 240.
            The dip between these high sunspot numbers also hints at two peaks. But what about the sunspot number around 210 in late 1999? Could this be considered a peak? If so, couldn’t the other daily maximums in the sunspot number be considered peaks? So could Cycle 23 have had many peaks?
            As for the end of Cycle 23, it’s somewhere in the 2008 time frame. Again the spiky data precludes pinning it down to a specific month.
            Since we’re having trouble pinning down the start and end and the peak – or peaks – let’s average the daily values to give us monthly means. (REMEMBER: The “mean” is the same as the “average.” – K9LA.)
            Figure 2 is the same data as in Figure 1, but with the monthly means added in dark blue.

Figure 2 – Cycle 23 daily and monthly mean sunspot numbers

            The monthly mean data is still kind of spiky, and does not allow us to pin down the start and end of Cycle 23 to a specific month/year. But at least we can now better see that Cycle 23 appears to have had two broad peaks.
            With respect to the peaks, should we take the two highest monthly means – about 170 in mid-2000 and about 150 in late-2001 – as the peaks? But what about all the other peaks in the monthly mean data? Should they figure in somehow?

Making It All Work ‘Smoothly’
            Enter: the use of the smoothed value.
            Now, hang on! The smoothed value for a desired month uses:
  • The monthly mean from the desired month
  • The monthly means from the five months before the desired month
  • The monthly means from the five months after the desired month
  • One-half the monthly mean from the sixth month prior to the desired month
  • One-half the monthly mean from the sixth month after the desired month
            Whew! Thus the smoothed value is heavily averaged. Also note that the smoothed value is six months behind the current month.
            The calculation of the smoothed value requires 13 months of data, but using one-half the monthly means at both ends results in 12 full-month data points. This can cause some confusion, as I’ve seen the smoothed value called a 13-month running average (since 13 months of data is required) and a 12-month running average (since it ends up with 12 full-month data points).       Regardless, the smoothed value is heavily averaged – in other words, it is smoothed.
            Figure 3 is the same data as in Figure 2, but now with the smoothed values added in green.

Figure 3 – Cycle 23 daily, monthly and smoothed sunspot number

            Now it’s easy to see that Cycle 23 indeed had two broad peaks – one in April 2000 at a smoothed sunspot number of 120.8 and the other in November 2011 at a smoothed sunspot number of 115.5.
            These months and smoothed values easily come from the raw smoothed data that is used to produce Figure 3.

That’s More Like It
            Now we can also easily determine a likely start and end for Cycle 23. We can simply use the lowest smoothed sunspot number for both.
            For the start of Cycle 23, May 1996 has the lowest smoothed value (8).
            For the end of Cycle 23, November 2008 and December 2008 have the lowest smoothed value (1.7).
            Be advised that these numerical minimums for the start and end times are usually the starting points – the official start and end times of a solar cycle can be revised a bit based on the comparison of old versus new sunspots and other factors.

Another Option
            Although I went through this exercise using sunspot numbers, I could have used 10.7 cm solar flux with the same results. That is, the smoothed value allows us to better determine the start time, the end time and the peak(s) of a solar cycle. This is why the official measurement of a solar cycle is the smoothed value.

Coming Up . . .
            February CQ Plus' Practical Propagation presents Part II of K9LA's series on why we need a smoothed solar index. This month he explains its value for making accurate propagation predictions. Visit <– KI6SN.