Tag Archives: Propagation

Solar Minimum Not Expected Until 2019 or 2020

So you think we are near the solar minimum and very shortly the cycle will start up again? Don’t hold your breath! Time to maximize your station’s effectiveness on bands below 15 Mhz!               Layne AE1N

Solar minimum not expected until 2019 or 2020

From: science.nasa.gov

High up in the clear blue noontime sky, the sun appears to be much the same day-in, day-out, year after year.

But astronomers have long known that this is not true. The sun does change. Properly-filtered telescopes reveal a fiery disk often speckled with dark sunspots. Sunspots are strongly magnetized, and they crackle with solar flares—magnetic explosions that illuminate Earth with flashes of X-rays and extreme ultraviolet radiation. The sun is a seething mass of activity.

Every 11 years or so, sunspots fade away, bringing a period of relative calm. “This is called solar minimum,” says Dean Pesnell of NASA’s Goddard Space Flight Center in Greenbelt, MD. “And it’s a regular part of the sunspot cycle.”

The sun is heading toward solar minimum now. Sunspot counts were relatively high in 2014, and now they are sliding toward a low point expected in 2019-2020.

While intense activity such as sunspots and solar flares subside during solar minimum, that doesn’t mean the sun becomes dull. Solar activity simply changes form.

For instance, says Pesnell, “during solar minimum we can see the development of long-lived coronal holes.”

Coronal holes are vast regions in the sun’s atmosphere where the sun’s magnetic field opens up and allows streams of solar particles to escape the sun as the fast solar wind.

 Sunspot Activity is low at Solar Minimum

Pesnell says “We see these holes throughout the solar cycle, but during solar minimum, they can last for a long time – six months or more.” Streams of solar wind flowing from coronal holes can cause space weather effects near Earth when they hit Earth’s magnetic field. These effects can include temporary disturbances of the Earth’s magnetosphere, called geomagnetic storms, auroras, and disruptions to communications and navigation systems.

During solar minimum, the effects of Earth’s upper atmosphere on satellites in low Earth orbit changes too.

Normally Earth’s upper atmosphere is heated and puffed up by ultraviolet radiation from the sun. Satellites in low Earth orbit experience friction as they skim through the outskirts of our atmosphere. This friction creates drag, causing satellites to lose speed over time and eventually fall back to Earth. Drag is a good thing, for space junk; natural and man-made particles floating in orbit around Earth. Drag helps keep low Earth orbit clear of debris.

But during solar minimum, this natural heating mechanism subsides. Earth’s upper atmosphere cools and, to some degree, can collapse. Without a normal amount of drag, space junk tends to hang around.

There are unique space weather effects that get stronger during solar minimum. For example, the number of galactic cosmic rays that reach Earth’s upper atmosphere increases during solar minimum. Galactic cosmic rays are high energy particles accelerated toward the solar system by distant supernova explosions and other violent events in the galaxy.

Pesnell says that “During solar minimum, the sun’s magnetic field weakens and provides less shielding from these cosmic rays. This can pose an increased threat to astronauts traveling through space.”

Solar minimum brings about many changes to our sun, but less solar activity doesn’t make the sun and our space environment any less interesting.

For more news about the changes ahead, stay tuned to science.nasa.gov


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

US Air Force Wants to Plasma Bomb the Sky Using Tiny Satellites

US Air Force wants to plasma bomb the sky using tiny satellites

The US Air Force is working on plans to improve radio communication over long distances by detonating plasma bombs in the upper atmosphere using a fleet of micro satellites.

The curvature of Earth stops most ground-based radio signals traveling more than 70 kilometers without a boost.

At night the density of the ionosphere’s charged particles is higher, making it more reflective.

This is not the first time we’ve tinkered with the ionosphere to try to improve radio communication and enhance the range of over-the-horizon radar. HAARP, the High-Frequency Active Auroral Research Program in Alaska, stimulates the ionosphere with radiation from an array of ground-based antennas to produce radio-reflecting plasma.

Now the USAF wants to do this more efficiently, with tiny CubeSats, for example, carrying large volumes of ionized gas directly into the ionosphere.

As well as increasing the range of radio signals, the USAF says it wants to smooth out the effects of solar winds, which can knock out GPS, and also investigate the possibility of blocking communication from enemy satellites.

One challenge is building a plasma generator small enough to fit on a cubesat – roughly 10 centimeters cubed.

The USAF has awarded three contracts to teams who are sketching out ways to tackle the approach. The best proposal will be selected for a second phase in which plasma generators will be tested in vacuum chambers and exploratory space flights.

General Sciences in Souderton, Pennsylvania, is working with researchers at Drexel University in Philadelphia on a method that involves using a chemical reaction to heat a piece of metal beyond its boiling point. The vaporized metal will react with atmospheric oxygen to produce plasma.

Another team, Enig Associates of Bethesda, Maryland, and researchers at the University of Maryland are working on a more explosive solution. Their idea is to rapidly heat a piece of metal by detonating a small bomb and converting energy from the blast into electrical energy. Different shaped plasma clouds can be generated by changing the form of the initial explosion.

David Last, former president of the UK’s Royal Institute of Navigation, is skeptical about USAF’s ambitions to counteract the effects of solar wind. When solar storms disrupt GPS signals, the entire side of Earth facing the sun is affected, he says. Ironing out those disturbances would require an extremely large and speedy intervention.

Written By David Hambling, this article was found at Daily News 9 August 2016 from the New Scientist web site: