10M Skip distance increased during the 20231014 eclipse for four WSPR TX

[Jim Willis]

All four showing an increase in 10 M skip distance caused by a decrease in foF2.

73,

Jim KX4TD

[Steve Cerwin]

..So for high freqs the eclipse shadow lowers foF2, but for low freqs a major effect is the degree of absorption of the D and E layers? Is that correct?
73, Larry
PS Congratulations on your daughter's marriage today. I think you are probably busy!

Hi Larry,
Yes busy is an understatement.

I believe your conclusions are correct. Here is my take on it. foF2 lowers from eclipse passage because the F2 layer is robbed of the ionization required to reflect higher frequencies at vertical incidence. If you look at the foF2 graphs you can see the critical frequency soars from nighttime levels when the sun comes up to increase ionization. I remember experiencing this firsthand on 75 meter in the early morning in regional roundtables with hams scattered all over the state of Texas. This was during the low years a few years ago when nighttime foF2 levels were well below 4 MHz. We would get on in the predawn hours trying to get the round table going and could barely hear each other. Then within literally a matter of seconds the signal strengths went from on the noise floor to 20-over 9! It was like someone had thrown a switch in the ionosphere. And something did - the sun. The slope of that morning rise in foF2 can be really steep. When the critical frequency rose through 75 meters things happened FAST. During the eclipse, passage of the shadow robbed away some of that ionization and recombination pushed foF2 back down because higher frequencies need more ionization.

For low frequencies too much ionization can be just as bad as too little. As this sunspot cycle progressed I noticed the 75 meter signal levels start to degrade as the morning wore on. By noon time you couldn’t even make a go on 75 meters over those same paths because of D layer absorption. It is my understanding the absorption happens because of energy lost in the radio wave by pushing free electrons around. It takes power to move them and the more of them the wave has to push the more signal that is lost. Things that make absorption worse are more free electrons in the D layer and lower frequencies. The lower frequencies have longer wavelengths and therefore have a greater chance of interacting with an electron. The eclipse shadow took away ionization in the D layer, tipping the balance between ionization and recombination in favor of recombination. Lower frequencies experienced less absorption during this time. I was transmitting the TDOA waveform every 15 minutes from 1130 to 1930 UTC on 60 and 40 meters. When the eclipse passed over Texas my regional contacts reported a noticeable increase in signal strength on their S-meters. You can see the profound effect the eclipse had on VLF signals on several of the excellent plots posted here. The increase in signal strength of 60 kHz WWVB was nothing less than profound.

73, Steve

[HL Serra]

Thanks, Steve. Excellent synoptic explanation of the practical effects of the eclipse, the ionization reduction and recombination effects.

BTW, what you describe as the 75m effect I believe is precisely what happens here in reception of 40m K Bcn signals on the west coast almost daily due to sunrise illuminating the high ionosphere over the US west coast even before actual local sunrise. We gain enhanced reception of 40m K Bcn signals for ~90 minutes within a 4 hr window every morning if North Pacific propagation conditions are not disturbed. Of the three daily periods of good 40m propagation from Asia to the US west coast (midnight local, 3am local and 5am-9am local) the 5a-9a window is always the most reliable, and we milk it like crazy in our CW contests.)

73, Larry

--
Please follow the HamSCI Community Participation Guidelines at http://hamsci.org/hamsci-community-participation-guidelines.
---
You received this message because you are subscribed to the Google Groups "HamSCI" group.
To unsubscribe from this group and stop receiving emails from it, send an email to hamsci+un...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/hamsci/4638FBD9-AFC6-440C-81EE-3B78F3C6EFC4%40cerwinconsulting.com.