HF Propagation - A Sunspot

Doom, Despair and Agony for HF Propagation

More Gloom, Despair, and Agony for HF Propagation

Sun quiet again as it heads toward solar minimum

By Meteorologist Paul Dorian, Vencore, Inc., vencoreweather.com

HF Propagation - Sunspot Cycle

Sunspot numbers for solar cycles 22, 23 and 24 which shows a clear weakening trend; current sunspot number indicated by arrow; plot courtesy Dr. David Hathaway, NASA/MSFC

The next solar minimum phase is expected to take place around 2019 or 2020. The current solar cycle is the 24th since 1755 when extensive recording of solar sunspot activity began and is the weakest in more than a century with the fewest sunspots since cycle 14 peaked in February 1906.  One other note, the weak solar cycle and the expectation for continued low solar activity this upcoming winter is an important factor in this year’s colder-than-normal Winter Outlook for the Mid-Atlantic region.

Solar cycle 24 – The sun goes through a natural solar cycle approximately every 11 years. The cycle is marked by the increase and decrease of sunspots which are visible dark regions on the sun’s surface and cooler than surroundings. The greatest number of sunspots in any given solar cycle is designated as the “solar maximum” and the lowest number is referred to as the “solar minimum” phase. We are currently more than seven years into Solar Cycle 24 and it appears the solar maximum of this cycle was reached in April 2014 during a spike in activity (current location indicated by white arrow).

The peak of activity in April 2014 was actually the second peak in solar cycle 24 that surpassed the level of an earlier peak which occurred in March 2012. While many solar cycles are double-peaked, this is the first one in which the second peak in sunspot number was larger than the first peak. The sunspot number plot (above) shows a clear weakening trend in solar cycles since solar cycle 22 peaked around 1990.

While a weak solar cycle does suggest strong solar storms will occur less often than during stronger and more active cycles, it does not rule them out entirely. In fact, the famous “superstorm” known as the Carrington Event of 1859 occurred during a weak solar cycle (number 10). In addition, there is some evidence that most large events such as strong solar flares and significant geomagnetic storms tend to occur in the declining phase of the solar cycle.

The last solar minimum phase lasted from 2007-to-2009 and it was historically weak. Consequences of a solar minimum – Contrary to popular belief, solar minimum is not a period of complete quiet and inactivity as it is associated with numerous interesting changes. First, cosmic rays surge into the inner solar system with relative ease during periods of solar minimum.  alactic cosmic rays coming from outside the solar system must propagate upstream against the solar wind and a thicket of solar magnetic fields.  Solar wind decreases and sun’s magnetic field weakens during solar minimums making it easier for cosmic rays to reach the Earth.  This is a more dangerous time for astronauts as the increase in potent cosmic rays can easily shatter a strand of human DNA. Also, during years of lower sunspot number, the sun’s extreme ultraviolet radiation (EUV) drops and the Earth’s upper atmosphere cools and contracts. With sharply lower aerodynamic drag, satellites have less trouble staying in orbit— a good thing. On the other hand, space junk tends to accumulate, making the space around Earth a more dangerous place for astronauts.


  • Now is the time to prepare for lower band activities. Twenty meters will take a back seat to 30- and 40- meters for DX work. Forty meters will become the top DX contest band.
  • Get those lower band antennas ready! (Maybe even delay the planned purchase of that triband beam!) A simple vertical ground plane antenna with 4-radials fed through a good tuner can be loaded on 10-80 meters as an effective antenna. A long wire as high as you can get it for NVIS (Near-vertical Incidence Skywave) propagation.
  • Close attention to propagation bulletins and spotted networks is needed. Since more hams are concentrated is a smaller spectrum, maybe even a linear amplifier for added ‘punch-power’ is warranted.

Layne, AE1N

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