With the recent disturbed and auroral conditions, this time we’ll take a look at how these type of conditions affect your ability to hear DX – or at least affect what you can hear as DX.

John Wilke, WB9UAI, Milwaukee, WI <J999w@aol.com>

I've done a fair amount of reading on the (effects of aurora on MW propagation) and if I recall correctly, it's usually stated that propagation through northern routes are attenuated leaving the possibility of the reception of southern stations. I don't remember much mention, if any, on east - west propagation. What I mostly notice during high geomagnetic activity from here in Wisconsin, is that the east coast is attenuated, leaving the door open for low power domestics, on a north - south path, even if they are located north of me. For example tonight, with auroral conditions, KDKA on 1020khz is attenuated leaving KJJK Fergus Falls, MN easily dominating the channel. Only on occasion do I notice a pipeline into the Caribbean, or Mexico as would be expected by reading the literature.

So, I guess my question is, what causes the degrading of the MW signal on the east west, mid latitude paths (such as Wisconsin to NYC)? Mark Connelly, often remarks that Africa is audible during auroral conditions because Europe is attenuated (crossing the auroral circle)... but that's east - west propagation which would be attenuated by my experience.

Secondly, with the earth’s magnetic flux lines being in different density in different parts of the world, would auroral effects differ as well? On an aside, I did have a nice greyline path into Mexico City at my sunset tonight. XEX 730khz came up out of the noise for about10 minutes, peaking S8, then faded right down to nothing again. Looking at the Geoclock map, both Mexico City and Milwaukee are on the terminus at my sunset. Textbook. Now if I can duplicate that half way around the world instead of 1700 miles !

Brent Taylor, Doaktown, NB <btaylor@nbnet.nb.ca>

Hi John, I'm far down the list of experts on this one, but I'll give it a try...

I'm guessing that your low-powered domestics are within groundwave distance, and therefore would not be attenuated by the Aurora, so if Au conditions exist, even northern groundwave stations should be fine.

Wisconsin to NYC would be far enough to require a significant skywave component to get the signal to the other end, and there are two factors that may interfere during Auroral conditions. First there is the fact that east-west at that distance involves a Great Circle path which carries the signal somewhat through a northern path. Second, the Auroral oval can extend far enough south (as it did Sunday night) to step on that Great Circle path and attenuate would-be east-west signals.

Milwaukee to Boston is a bearing of 86 degrees true, so even though Boston is SOUTH of Milwaukee by half a degree of latitude, a signal from Boston to Milwaukee, by the shortest path, actually travels slightly to the NORTH, and therefore has a better chance of being attenuated by the Aurora when it is present.If you do a Great Circle path to both Africa and Europe you will see that Europe's signals pass far farther north than Africa's, but even Africa's signals have a North-East component to them. For instance, Boston to Hamburg, Germany is at a bearing of 46 degrees, and Boston to Western Sahara is at a bearing of 89 degrees. If the Auroral oval lies between those two bearings, as it often does, European signals will be attenuated greatly, while African signals can arrive relatively unscathed.

Yes, I believe (auroral effects differ in different parts of the world). Because there magnetic north pole is actually in Canada, several hundred miles south of the "real" pole, the Auroral "donut" is shifted towards North America, with the hole of the donut therefore over Ellesmere Island. The Auroral oval therefore extends further south into North America than it does on the European-Asian side of the planet.Thomas Giella, KN4LF, Plant City, FL <kn4lf@tampabay.rr.com>

I think Brent Taylor did an excellent job answering of answering John Wilke's propagation questions.

As far as the last question- "Secondly, with the earth’s magnetic flux lines being in different density in different parts of the world, would auroral effects differ as well?" I would like to add that under definition #1i on my propagation theory notes at http://www.kn4lf.com/kn4lf8.htm I have four maps of our Earth’s magnetic field density differences.

Also there is a beast called Magneto Ionic Power Coupling. Antenna polarization plays a large role in the success of a long haul MF DX contact. As a medium frequency RF signal traverses our planets magnetic lines of force in a perpendicular manner on high and mid latitude paths say between W3 land and SM, higher angle horizontally polarized signals are more readily absorbed then lower angle vertically polarized signals. On other propagation paths on the globe opposite results can be found, i.e. horizontally polarized signals suffer less absorption on a propagation path between VK6 and W4.Marc DeLorenzo, Marstons Mills, MA <MarstonsMarc@aol.com>

John- Brent Taylor's explanation was excellent! I recommend that you look at drawings of the auroral oval in various positions. Such drawings can be found in NRC reprints of articles written 30-35 years ago by Gordon P. Nelson. Go to http://www.nrcdxas.org/catalog/reprints/ and scroll down to "Propagation." The articles that are likely to have such drawings include P1, P6, P7, and P13. Other DXers (including Russ Edmunds) have also written excellent articles on this subject.

Russ Edmunds, Blue Bell, PA <wb2bjh@nrcdxas.org>

I would also recommend viewing such sites as

www.spaceweather.com

www.sec.noaa.gov/radio/radio.html

www.sel.noaa.gov/today.html

These will show near real-time views of the earth and the positioning of the auroral zone at different times of day.

John Wilke <J999w@aol.com>It appears that most of the low power domestics I hear during auroral conditions are in the 400 to 600 mile range... could it be that I'm hearing them via D layer rather than E layer skip? Is the E layer affected more by the auroral conditions than the D layer?

Thomas Giella <kn4lf@tampabay.rr.com>The RF signal absorptive radio aurora is at the same approximate altitude as the E layer. As the E layer is the primary refractive layer for the MF AM broadcast band it explains why the radio aurora is a negative thing.

As far as the D layer it can refract or actually wave guide in a sense, frequencies below approximately 300 kc at day. At daytime the D-layer, which is at an approximate height of 30-60 miles in the mesosphere, totally absorbs medium frequency RF signals, most of the time. I say most of the time because at high latitudes, during the winter season and especially at the low part of a sunspot cycle, penetration of MF RF signals through the weakened D-layer and then refraction via the E-layer does occur. Also the D-layer does not totally disappear at night. Many books that deal with radio wave propagation erroneously state the D and E-layers disappear after sunset, totally incorrect thanks to Galactic Cosmic Rays. Background electromagnetic radiation in the 1 to 10 Angstrom range (Hard X-Rays) from our Sun is the main source of ionization of the day time D-layer. While I'm visiting the subject of electromagnetic radiation, our Sun emits electromagnetic radiation and matter, as a result of the nuclear fusion process. Electromagnetic radiation at wavelengths of 100 to 1000 Angstroms (Ultraviolet) ionizes the F region, radiation at 10 to 100 Angstroms (Soft X- rays), as well as Cosmic Rays ionize the E region. Galactic Cosmic Rays are the reason that the E layer is "always" present at night time, the D layer also to a lesser extent.

Barry McLarnon, VE3JF, Ottawa, ON <bdm@bdmcomm.ca>Here's my take on it. You're still hearing signals via the E layer (or possibly F layer, especially if you're at the high end of the band). For a given station, skywave field strength would be an inverse function of distance if its antenna radiated equally at all elevation angles, due to the usual 1/distance-squared spreading loss (calculated for the ionospheric path, of course). But the antenna is designed to maximize low-angle radiation, for groundwave coverage. This causes an increase of skywave field strength with increasing range along the ground, at least up to the point where the angle becomes low enough that ground losses (at both the transmit and receive ends of the path) start to become a significant source of attenuation. These two factors balance each other and produce a broad maximum in field strength as a function of distance - probably somewhere around the upper end of your 400-600 mile range.This applies to typical nighttime conditions in the winter, but in the summer when there is often some residual D layer absorption at night, or anytime when there is auroral absorption to contend with, we have to throw this factor into the mix too. A signal suffers more attenuation if it travels through the absorbing layer obliquely, so this factor also causes a decrease in field strength with increasing path length. Also, multi-hop signals get hit by the absorption multiple times, so they get attenuated even more. The result is that the maximum field strength as a function of path length gets shifted to shorter distances, so closer-in stations are relatively stronger than at times when absorption isn't a factor. And, of course, if you are anywhere near the auroral oval, direction of the path becomes a huge factor too.Thomas Giella <kn4lf@tampabay.rr.com>Barry’s take on it is also very plausible. On my propagation notes website I have this posted.

2.) Aurora Oval Blockage, Absorption And Refraction-

The aurora ovals "generally" have a negative impact on medium-frequency propagation. If the path over which you are communicating lies along or inside one of the Aurora Ovals, you will experience degraded propagation in one of several different forms; strong signal absorption, brief periods of strong signal enhancement, which is mainly caused by tilts in the ionosphere that allow signals to become focused at your location or very erratic signal behavior in the form of strong and rapid fading, etc., caused by a variety of effects such as multi-pathing, anomalous and rapid variations in absorption, non-great-circle propagation, horizontal or side refraction and/or scatter (skewing) due to changes in electron density and polarization changes. (See definition #7. Propagation Path Skewing).

When the Aurora Oval zones are contracted and latitudinally-thin coinciding with low geomagnetic activity, it is possible for a medium-frequency transmitted signal to propagate through the Aurora Oval zone without being heavily absorbed by skirting underneath it.

During periods of very low geomagnetic activity, areas of the Aurora Oval zones may only have a latitudinal thickness of approximately 300 miles. But radio signals reflected from the E-layer can travel over distances of as much as 300 to 1100 miles at heights below the ionosphere for low take-off angles of between 10 and 25 degrees. When the geometry is just right, the medium-frequency transmitted signal can literally propagate underneath and through the Aurora Oval zones into the polar ionosphere which is less disturbed and from the polar ionosphere back into the middle latitude ionosphere, without ever coming in contact with the highly absorptive Aurora Ionosphere. This type of propagation is not as rare as you might think and it can provide unusually stable polar region path openings to (TA) Transatlantic and (TP) Transpacific regions. But because the Aurora Oval zone expands and contracts constantly, such conditions often do not last very long.

Benjamin Dangerfield, Wallingford, PA <ben-dangerfield@verizon.net>Barry & Thomas: Your explanations are interesting, but do you have to use so many big words? I am not a technical expert and get lost on trying to get the gist of this stuff. And in the same vein, are you also saying that long distance reception is worse in the summer because of different angles of the sun? I have always felt this to be the case, at least at inland locations like mine.

Thomas Giella <kn4lf@tampabay.rr.com>

I always try to explain propagation in layman's terms but at times it's hard to do sometimes without losing the meaning. I actually take a lot of criticism from my colleagues for simplifying propagation mechanism explanations. On my HF/MF propagation theory notes website I have posted:

.....I have attempted to keep the following propagation theory explanations in simple to understand layman terms, because long complicated technical explanations can be boring and make one's eyes glaze over. Unfortunately though sometimes while trying to keep things simple, certain definitions, meanings and technical aspects can get watered down or even lost, which tends to open me up to criticism from fellow space weather scientists that just don't understand the educational and public relations concept of keep it simple stupid (KISS) principle. I choose to use W6SAI's (SK) "KISS" method of writing and communicating. I have found that this method works best whether it be in teaching about Space Weather or Atmospheric Weather. I have an extensive teaching background in Space and Atmospheric Weather.....In general stateside MF AM broadcast band signals are weaker in summer time, as there is less darkness and the D-layer is more ionized for a longer period of time due to the higher angle of the Sun, therefore more absorption. Also the F-layer is less ionized in Summer versus Winter due to different chemical reactions in the upper atmosphere. This effects long haul DX in a negative way because the F layer is the other half of the E-Valley/F Layer duct mechanism and also the medium for Chordal hop propagation.John Wilke <J999w@aol.com>What I'm noticing during auroral conditions:

- Reduced east coast station strength from here in the midwest, 600-800 miles.- Increased strength of low power stations to the NW, W, and S of me generally from 400 to 600 miles out.I'm thinking that because the auroral oval is to my north east, it's going to have a greater impact on stations to the NE and E of me, compared to stations W and S. For this reason, if the storm isn't too big, east coast signals are attenuated while signals west and south of me can reach me relatively unscathed giving the appearance that they are louder than normal.

Still, some of these 100 - 200 watters are reaching S9+20db during auroral conditions that I never seem to notice otherwise. It may be because I never bother to park on KDKA or such to see if they appear or not.

Still, I'll take a new station anyway I can get it.

Barry McLarnon <bdm@bdmcomm.ca>

Precisely - "if the storm isn't too big, east coast signals are attenuated while signals west and south of me can reach me relatively unscathed giving the appearance that they are louder than normal."As you say, they give the appearance of being much stronger than normal, but I think that's just your receiver AGC pumping them up in the absence of your usual pests to the east. Presumably, you could accomplish much the same thing under more normal conditions if you were able to get an exceptionally deep null on the pests... ask Kaz for tips on that.:-)David Hochfelder, Highland Park, NJ <david.hochfelder@rutgers.edu>Here's my impressionistic and decidedly non-technical view of what happens to my DXing during auroras. During a strong aurora I lose the Chicago clears completely, and hear Venezuelans, Colombians and Cubans there, with Jamaica about a third of the time on 720 and 780. St. Kitts on 555 is somewhat improved, but there's not much on 550 or 560 that an aurora blocks to help QRM from those channels. Cleveland and Detroit clears are weaker but still present. Montreal, Toronto, and Boston stations are basically unchanged unless the aurora is very strong and reaches quite a bit southward.So the aurora wipes out propagation from the west and not from the north, at least here in central NJ.

Thomas Giella <kn4lf@tampabay.rr.com>

http://www.kn4lf.com/kpmap.gif Here is an image that I have on my propagation website at http://www.kn4lf.com/kn4lf5.htm. It shows you the geomagnetic latitude of the Aurora Oval versus the Kp value. At the height of the most recent geomagnetic storm of a few days ago the Kp was 9. You can see how far south (red line) that the Aurora reached and it can give you an idea of how your location was oriented for blanketing or blockage of MF AM broadcast band stations.