[BC] Re: Fwd: FW: PRE AND POST HOURS

[r j carpenter]

<pedantic mode: ON>

The F layer does not dissipate at sunrise. The absorptive D layer comes 
into existence when sunlight reaches it. This essentially eliminates 
long-distance propagation on the AM band (below the gyro frequency). 
The effect on AM propagation might be about the same, but the mechanism 
is different.  In low sunspot number years the gyro frequency gets down 
into the top of the AM band - thus "daytime skywave".

<pedantic mode: OFF>

bob c.