Topband: what form of propagation?

[k9la at frontier.com]

Jim (K9YC),
 
You asked : So I'm wondering what form of propagation this is at this time of day? Could it be ordinary ground wave?
 
Several years ago I wondered about that, too, since I can easily work the East Coast from Ft Wayne (IN) at noon on 160m on CW with 1000W to my inverted-L. Thus my May/June 2006 NCJ Propagation column analyzed this using 1000 W.
 
In a nutshell, if we assume CW with 1500 Watts to quarter-wave verticals over average ground and a quiet rural noise environment (about -103 dBm in 500 Hz), our model of the loss in the D region around noon on a winter day at solar minimum allows QSOs out to 1500 km (938 miles) or so before the signal is at the noise level. I also believe our model of D region absorption is a bit pessimistic for the aforementioned conditions (VY2ZM's monitoring of the GB3SSS beacon in December 2006 is the main driver behind this belief - which was discussed in my December 2007 Propagation column in WorldRadio).
 
So it's likely that these QSOs (and SWL reports) are a single hop via the E region. I just don't see ground wave coming into play here - way too far for ground wave based on GRWAVE.
 
Carl K9LA