On Thu, 15 Jul 2010 11:41:53 +0000 (UTC), Kevin Alfred Strom
wrote:

dave wrote:
[...]

You need UV radiation to energize the upper atmosphere. Sunspots are
where the UV rays come from. It's in your Extra Class test.



Yes, I know about the ionosphere. But what I am trying to say is
that more radiation is not always "better." And there's always some,
even at sunspot minima.

For example, during the bottom of the solar cycle, 75 meters is
alive during the day, with stations heard many hundreds of miles
away with good signals. Near the top of the cycle, the absorption is
so high, you can hardly hear any stations at all daytimes on 75.


With all good wishes,


Kevin, WB4AIO.

I think that corona holes and the resulting solar windstream are the
biggest disruption to propagation. At least here in the higher
latitudes. We had an impact last night and the bands are in noticeably
poorer condition today even though the K index is back to 2 (5 last
night).

http://www.swpc.noaa.gov/rt_plots/kp_3d.html

Jim