When the ionosphere gets "switched" on ?

I've been looking at my 10Mhz WSPR observations.

Seems to me that:

The ionosphere become useable one hit by the suns rays at local civil sunrise.

Civil sunrise being defined when the sun is at +6 degrees from the observer site, as opposed
to astronomical or locally defined sunrise which has a massive 2 hour difference in defination !

Ionospheric switch off time always seems to take longer as the ionosized particle recombine, so I assume
that it's easier to ionise and takes longer for the ionised particle to re-combine, although it still seems
that once civil SUNSET occurs the band does *start* to decline.

Comments ?

73 de Andy