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.