I’ve had the hobby of radio MW/SW/FM and television DXing since I was in elementary school. I’ve received distant stations via a number of propagation modes. I have received distant AM and SW via “skip”, which is refraction of a skyward radio wave back towards the Earth by the ionosphere. This is often referred to as a “reflection”, but that is technically incorrect. If it were a reflection, a signal straight up would be reflected back, but that is not the case.
The ionosphere is a layer of the Earth’s atmosphere, extending from about 50 miles up to several hundred miles, ionized primarily by UV radiation from the Sun, also to some degree by cosmic rays. UV from the Sun is mostly from the chromosphere, an area above the visible photosphere which is occasionally visible as a rosy red glow during a solar eclipse.
The UV flux from this chromosphere varies with the level of solar activity and is generally low during solar minimums and high during solar maximums. The higher the level of UV flux, the greater the degree of ionization in the ionosphere. The stronger the ionization, the greater the refraction at a given radio frequency. This means that as the ionization increases, higher frequencies can be refracted back towards Earth.
Because UV flux is non-existent at night, that source of ionization is absent at night and the ionosphere is weakly ionized. The lower altitude regions tend to go away as the charged ions and electrons recombine into neutral atoms. Only at higher altitudes, where the density is low enough that collisions are less frequent, does significant ionization remain at night. Ionization is also generally lower during solar minimums as well because of lower solar UV flux output.
Image courtesy of SOHO/EIT consortium. SOHO is a project of international cooperation between ESA and NASA.
What you are seeing here is an image of the Sun that is completely lacking in sunspots. It has been this way since July 24th, 2007. We are presently in a solar minimum. This means that ionization of the ionosphere should be minimal as well, particularly at night.
The higher the radio frequency or the shorter the wavelength, the less the ionosphere will refract the radio wave. Consequently as the radio frequency increases, signals can only be refracted back to Earth if they arrive at the ionosphere with a low angle nearly parallel, a signal entering at a high almost perpendicular angle would not be refracted sufficiently and would pass through the ionosphere or be absorbed by it. At lower frequencies signals can be refracted back at sharper angles.
Above some frequency a signal can not be refracted sufficiently to return to Earth even if it arrives at a very low angle. The highest frequency that can be refracted back during given ionospheric conditions is known as the maximum usable frequency or MUF.
Two days ago, at 11pm, I was still able to receive WWV at 15 Mhz and I listened to Radio Japan at just over 13 Mhz for almost two hours and the signal was strong. I was able to detect some skip at frequencies above 17 Mhz, however, because of computer hash I wasn’t able to make out what it was.
This is really abnormal behavior during a solar minimum. During a solar minimum this reception would be more typical of daytime reception. At night it is generally not possible to receive anything distant above about 7-8 Mhz. The MUF is only about 7 or 8 Mhz at night during solar minimums, but two nights ago it was over 17 Mhz for at least a couple of hours.
Sometimes space events called gamma ray bursts can significantly increase ionization of the ionosphere. Gamma ray bursts generally last milliseconds to several minutes. Radio Japan came in strong for several hours and maybe more as I did not continue to listen.
Lightning storms also can dramatically increase ionization at night, however, generally in a limited geographical area, yet, I was receiving WWV on 15 Mhz from Ft. Collins, CO, and Radio Japan, so whatever phenomena resulted in this high level of ionization was geographically more disperse.
Given a Sun which was not active, and the lack of a fit to other known sources of nighttime ionospheric ionization, I am puzzled as to what is responsible for the high degree of ionization.
During the last solar maximum, the MUF reaching above 50 Mhz was almost a daily occurrence for months at a time. That was unusual, but the last solar maximum was also unusual, the most sunspots of any recorded maximum. Chinese and Tibetan monks have been recording sunspots for thousands of years. Western records date back several hundred years. Strong ionospheric activity during the last maximum is not surprising but the level of activity during this minimum is.
I mentioned that television DXing is one of my hobbies. Most frequently, TV DXing is in the low VHF band, channels 2-6, during solar maximums. Occasionally there are what are known as sporadic E-skip events as well. These happen most frequently during summer, during afternoons, but they can happen anytime and I have seen events in the middle of the night, in the winter time.
During this last solar maximum, I received channels via skip all the way up to channel 10, which is at 192-198 Mhz. I only experienced skip at this frequency once, it is extremely unusual, and unfortunately it did not last long enough to get a station ID, so I don’t know the distance involved which would have revealed more about the nature of the skip. I received skip on channel 8, 180-186 Mhz on several occasions.
Skip at low frequency channels, channel 2 or 3, at 54-60 Mhz or 60-66 Mhz respectively, was a rare event when I was young, thirty years ago, I might receive skip on these frequencies several times generally during afternoon late summer hours. It seems to have become more and more frequent over the years to the point where now in any two week period I can usually pick up something just listening sporadically.
Ionization seems to have increased gradually over the years on average and I am very interested in knowing the source. I have also noticed that while shortwave and low VHF propagation have improved over the years, absorption in the AM broadcast band (540 – 1700 Khz) as well as the low shortwave frequencies between the high end of the AM band and around 5 Mhz, seems to have increased.
Another area that seems to be related is auroras. I have lived in the Seattle area all of my life, first near Northgate, and then for the last 22 years in Shoreline, approximately 7 miles north of Northgate. When I was a kid, I used to sleep outside on the patio on clear summer days falling asleep under the stars. Never once did I see an auroral display in all of those years. I have now seem them five times and all within the last decade, and this during a time when I spend much less time outside under the sky.
With respect to Auroras, the last heavy duty solar cycle might explain those, but it does not adequately explain the changes to radio propagation even during solar minimums. I am convinced that either something in our Sun is changing significantly, or something in our own atmosphere.
The amount of carbon dioxide and methane in our atmosphere has been increasing as a result of human activities. The distribution of water vapor and ozone in the atmosphere is also affected by human activities. At 350 PPM or .035%, I would not expect carbon dioxide to significantly impact the ionosphere. Carbon dioxide is also heavy so I would expect it to make up an even smaller percentage of the ionosphere.
Then there is HAARP and other similar installations that intentionally heat a portion of the ionosphere, but these are tightly focused beams, so I would not expect widespread geographical changes, however, I have heard that there is now a system in place to destroy inbound warheads electronics by supercharging the ionosphere, so maybe the capabilities are greater than I know. However, this seems to be a gradual effect and HAARP at higher power is a relatively recent phenomena.
I wonder if all the space missions don’t contribute somehow, the rocket exhaust, the re-entering of space debris, do they significantly alter the ionosphere on a large scale?
Then there is the general increased use of higher frequencies, more power in the microwave band. Could these be affecting overall ionization levels?
How about 50 and 60Hz radiation from long distance AC power transmission lines? We know these have some effect on the ionosphere and magnetosphere because whistlers often start at these frequencies (though they are most often triggered by lightning events).
And I know this may seem really far fetched, but could Gaia play a role? The reason that I asked this is that I’ve listened to a phenomena where a large audio frequency antenna is used to pick up signals from the Earth’s magnetosphere. Here listen to this. Tell me that doesn’t sound alive and organic to you.
Please, tell me if you’ve observed any related phenomena and what you think might be the cause.