Baffled in Vancouver

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Baffled in Vancouver

Postby ve7aop » Fri Dec 19, 2003 5:34 am

The A index is 6, the K index is 1 - the aurora oval is miles from my QTH, yet the bands are dead at 04:00 UTC - nothing for days. I am trying 40 and 30m. No problem before about 02:00UTC - lots of signals - no problem getting out - even DX once in awhile. But after the sun goes down, nothing. The FOT chart,, shows that something should be open from 0200 or 0300 on thorugh the night. Even the AM broadcast stations on 40 are weak and muted. NW7US reports "The very large coronal hole that has kept the geomagnetic field at active to minor storm levels is no longer in view. This is giving us a nice period of quiet geomagnetic activity, with the result being that we are seeing propagation that is more normal over most of the paths around the world." and "This translates to some very good conditions for the High Frequencies (HF). " However this is not correlating to my present experience. Please help me understand what is happening at night after 0300UTC between 7 and 10 MHz.
Thank you ,
Ralph - VE7AOP

The start of an answer...

Postby NW7US » Fri Dec 19, 2003 6:28 am


well, that is a great question. I am also in the middle of some research regarding the usage of frequencies in the 80 meter band at about the same time frame (0300 to 0600 UTC) for regional traffic.

The daily situation is more complex than just looking at the table of usable frequencies between two general areas (my chart). First, that chart was created using a more southerly West Coast location. And, the general area of the other end is very specific, and might not represent fringe areas.

Secondly, the chart shows the frequency most likely to be at the top of the range of frequencies that might be supported between the two locations. However, in the real world, other factors may change this.

Of course, we know that a geomagnetic field disturbance lowers the ionization of each ionospheric layer by some factor. This lowers the MUF from what is "normal." Other factors (like a high background X-ray level, or, the influence of a flare), may increase ionization - especially in the D-layer, causing a rise in the absorbed frequency - meaning that, starting at the lower HF frequencies, then moving higher in frequency depending on the intensity of the D-layer ionization, the signals will get absorbed. So, let's say that we expect 7 MHz to propagate beween the Southwestern area of the US and the Pacific Northwest. At the same time, we might have a higher background X-ray level that will keep the D-layer somewhat ionized (it is not true that the D-layer completely disappears at night, especially during the peak years of a solar cycle). So, let's say that the D-layer will partially absorb frequencies up to about 5 MHz, with some continued, but less, absorption up to, say, 8 MHz. That will degrade the predicted 7 MHz MUF. Some propagation of strong signals will occur, but the signals will be weakened. And so on...

Indeed, the background X-ray radiation is higher than it has been over the last week:

Code: Select all
#                         Sunspot       Stanford GOES12
#           Radio  SESC     Area          Solar  X-Ray  ------ Flares
#           Flux  Sunspot  10E-6   New     Mean  Bkgd    X-Ray
#  Date     10.7cm Number  Hemis. Regions Field  Flux   C  M  X

2003 12 11   86     35      270      0    -999   A7.7   0  0  0
2003 12 12   87     36      220      0    -999   A7.4   0  0  0
2003 12 13   88     40      210      1    -999   A9.7   0  0  0
2003 12 14   92     48      220      0    -999   B1.3   2  0  0
2003 12 15  101     42      150      0    -999   B2.0   0  0  0
2003 12 16  106     71      340      3    -999   B2.4   1  0  0
2003 12 17  118     92      330      2    -999   B3.8   4  0  0
2003 12 18  123    114      510      1    -999   B5.2  16  0  0

From this, we see the background X-ray radiation going from the high A-level, to the middle B range. At the same time, look at the number of flares. While there were no moderate nor major flares, there were a high number of C-class flares (16). This has caused the D-layer to be more ionized than normal, closing the gap between the lowest frequency that can pass through the D-layer, and the highest frequency that the E or F layer will refract back.

Take a look at this:

Pick the hours that you have in question, and pick San Francisco.

The results show possible Optimal Frequencies between the West Coast and the rest of NA. But, take into consideration that the D-layer, or other factors, might cause degradation.

At the same site, look at the T-map for North America. Right now, it is showing some degradation (still) for the West, and significant degradation still for the Eastern USA. Remember, it takes a few days to see conditions improve overall, after seeing the geomagnetic field quiet down.

That brings me to another thought - While the path shows a frequency that might be usable, a local depression might be taking place, too. Your local environment might be less-than-optimal. That might be noise levels, or even a localized ionospheric depression. Interesting thought...

Another site to look at, for your area, is:

This is a first attempt at an answer. I am still looking into this topic, as it is a current topic for a local group and I wish to find a useful answer and model for what is happening in the real world.

Thanks for your question.
73, de NW7US (Tomas David Hood)
.. Contributing editor, Propagation Columns in:
.... CQ Magazine, CQ VHF Quarterly, Popular Communications Magazine

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My Amateur Radio hobby... | YouTube - NW7US Channel | NW7US on Facebook | Space Weather and Radio on Facebook
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Postby ve7aop » Fri Dec 19, 2003 7:46 am

Thanks Tomas for your reply. D layer absorption and X-rays make sense. D-layer and X-rays is an area I have to spend more time studying and getting familiar with the various metrics. Noise levels right now at this QTH are S6/7 on 80m, S3/4 on 40m and same on 30m. In one way noise is my friend, in the sense that if I can hear noise I know my antenna is still connected and my receiver working! Over the last several weeks the bands tend to open up around 3PST. This lasts for a few hours and once the sun goes down its all over. Solar weather and impact on HF propagation seems to be almost an intractable subject. We will watch what happens over this weekend. Thanks for the new links - more good stuff. (I was totally unaware that the Canadian government maintained a space weather site.)

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