Ham Radio Forum

A frequently asked question is 'What types of ionospheric events can I monitor?'

This is the fun part of SID monitoring because there are so many things to look at, including a few mysterious events that I still can't put my finger on, but I'm working on it (I'll post more info later). For now, here's a list of seven types of events and an explanation for each:

1) Local Sunrise / Sunset effects
2) Daytime effect
3) Nighttime effect
4) Solar Flares (Class C2 and up)
5) Lightning ++
6) Meteors ++
7) Gamma Ray Bursts (GRB) / Soft Gamma Repeaters (SGR) ++

1) I'm sure you would expect the ionosphere to change with the advent of the sunrise or sunset, but if you are monitoring a VLF station in a different longitude than your own then you can see the effect shifted by and hour or two. (I'm sure a study can be done to explain what is going on there). For the classic sunrise effect I normally see a positive spike above the nighttime noise about one hour before local sunrise. It is followed by a plunge in intensity and a much smaller local maximum around the time the sun is at the horizon. About an hour after sunrise there is a smaller hump before the normal daytime pattern begins. Sunset is not as exciting, but the ionization effect decays and the signal strength goes up as it enters into the typical chaotic nighttime pattern.

2) After the sunrise effect, the normal daytime pattern is like a hump; where your local noon is the highest point on that hump and we set the noontime point at 1/3 the total scale. For our monitor it would be -1 to -1.5 volts, on a scale between -5 and +5 volts. This allows enough headroom for the most massive of X-class flares but still enough sensitivity for smaller C-class flares - we cannot be sure of the direction of the flare, so we are basing our setting on empirical observations and they have held true for the 3+ years we have been performing these observations.

3) The nighttime effects appear random and unpredictable. A lot of the annoying nighttime DX radio fading is an example of this. Solar effects on the ionosphere will not occur, although I do have a thing or two to say about that perhaps in a later post. For the most part, the nighttime data is noise and not interesting to us, but it depends on whom you ask. There is another group at Stanford that studies nighttime phenomena such as lightning, sprites, blue jets, elves, etc. and their daytime data is their 'noise.' By combining our efforts we share the data so we can study both types of effects. Sorry, I do not study these events so I can't add more details than that, but perhaps later...

4) The X-ray flux from the sun is ranked on a logarithmic scale based on the energy in watts per square meter. The flare ranking is based on the highest peak of the primary satellite (currently the GOES-12) 1 - 8 angstrom bandpass filter. Empirically I have noticed that the ionosphere starts responding in a noticeable fashion at approximately a C2 flare, which has the energy of 2.0x10^-6 W/M^2, however this is not always the case; I have detected at higher and lower energy thresholds depending on the time of day, and condition of the ionosphere. Additionally, you cannot observe ionospheric effects of solar flares during nighttime, but maybe in a diminished capacity coming out of sunrise or going into sunset effect.

A solar flare can have one of two effects to the VLF propagation: It can attenuate the signal strength or increase the signal strength. What the effect will do is based on multi-node wave interference, path of propagation, wavelength, number of bounces, and some other factors I am probably not adding in.

I have been asked about the possibility of constructive and destructive interference of sky- and ground-waves. I do not believe that ground-wave interference plays a role in the detector as we are using an inductive sensing method that receives the b-field of the sky-wave. The e-field induced by the ground-wave appears to be about 100+ times weaker.

My observations of the RF sky-wave propagation of 24.8 kHz from NLK @ Jim Creek, WA to Stanford, CA have been positive going signals. They shoot up in a period of 1 or 2 minutes, and then depending on the length of the flare and the intensity, the ion-recombination (AKA the recovery) of the ionosphere takes over the period of tens of minutes slowly. The closest thing I can say that it looks like is a shark-fin. I mostly see positive signatures, however I have on occasion seen a negative-going flare signal.

5) Lightning ++
Your typical atmospheric type of weather phenomena... it has two effects: ionization of the atmosphere and transmits broadband noise simultaneously. Depending on distance from the monitor can create overwhelming noise and disrupt solar SID monitoring. Lightning safety should be #1. We have already had one monitor go down because of lightning.

6) Meteors ++
Space junk falling trough our atmosphere. During expected meteor showers I am told that some HAM radio operators use the ionization effect to try and make DX contacts. These events would be observable at nighttime only (because the daytime ionization dampens the signal)

7) GRB's / SGR ++
Gamma Ray Bursts are produced from exploding stars called magentars. A major event on Dec. 27, 2004 at 21:30:26 UT ionized the atmosphere from 50,000 light years away (Think about that for a second... There was enough energy to travel 50,000 years and still ionize our atmosphere... WOW!). GRB's are usually short-lived events and are mostly observable only at nighttime for the same reason as #6 above, but this event was spectacular as it actually was observed during the daytime and competed with the sun!
http://skytonight.com/news/3310066.html?page=1&c=y


++ = Not available on a Solar SID Monitor. Here's why: The Stanford Solar SID monitor cannot detect these events because we had to put a dampening circuit (~2-second R-C time delay) to make the effects of solar SID's stand out above the noise that primarily comes from lightning (*) that can be 100's of strikes an hour. A graph without this dampening circuit looks fuzzy and smaller C-class solar flares disappear into that noise. Since a solar SID takes tens of minutes to develop and persists longer than these shorter-lived events, the Solar SID Monitor is better suited at recording solar events.


(*) This is not 100% true... when lightning storms are persistent, especially when monitoring long distance they do show up.

For the data collecting purists in the crowd, and a frequently asked question / criticism about the Solar SID Monitor, is that we have filtered out these interesting events. It isn't fair to say that we are not interested in these events because we were addressing a specific use in a classroom for use in the daytime and focused on solar induced ionospheric effects, it can only do so much.

The reason why we chose to use a filter instead of mathematical removing it from the data is because it was simpler (we tried that initially). We currently collect a sample once every 5 seconds that takes 490 KB / day. To combat the constant snap, crackle, and pop of the lightning strikes we would have to sample at a higher rate, producing much larger files, then average out, like the electronics would have done, but how to achieve the clean signal trace given the limited tools and computing resources etc...? The problem was easily solved with about 70 cents worth of components.

For that we also have another ionospheric / space weather monitor called AWESOME that was designed by the EE VLF group - that is the other group I mentioned that studies the nighttime ionospheric data. It carries out hi-definition scientific research of the ionosphere - it's the "real deal". They collect everything from 0 to 50 kHz, at over 100 KSPS, and it uses two antennas to detect phase, intensity, and direction, but they are not simple to use and install- because they require a lot more space for the dual antenna array, maintenance, computing power, and more. They cost over $3000 and require a commitment that is more suitable for a research facility than a college or high school.

The SID monitor is designed for high school and college teachers, ham radio and/or hobbyists that want a simple device to monitor space weather that affects the ionosphere. For those that want to monitor the transient events, then it is a simple change of the RC time constant and to increase the data collection cadence and perform the filtering in software.

We have our monitors here. These are primarily for educators:
http://solar-center.stanford.edu/SID/sidmonitor/
The plans and software are also posted on-line if you want to build one yourself.

AAVSO has plans for simpler SID circuits that you can build your own:
http://www.aavso.org/observing/programs/solar/equipment.shtml


For now 73's and happy SID monitoring.