On 06/06/2015 14:54, Joe Taylor wrote: > Hi Bill, Steve, and all, Hi Joe,
... > > As a placeholder, in the present routine grayline.f90 I defined the > grayline to be centered at the time when the sun is 50 arc minutes > (0.8333 deg) below the local horizon. This is normally taken to be the > time of sunrise or sunset. Of course, for ionospheric propagation > purposes what matters is whether the sun illuminates a specific layer of > the ionosphere. The end of D-layer illumination occurs when the sun is > something like 6.6 deg below the horizon. (The end of F-layer > illumination more like 14.2 deg below the horizon, but I think it's > D-layer absorption that we're most concerned eith here.) > > So... would it be better to center our grayline periods at the times > when the sun is about 6 degrees below the horizon -- also the end time > of what's normally taken to be "civil twilight" ? I am not an MF/LF propagation expert but I do know one and I will consult with him later. I have vague recollection that gray line paths are definitely timed and influenced by the slope of the terminator due to the glancing angle and also there is some lag in the effects. Given that the actual enhancement when it happens is usually only for a few minutes assuming suitable placed local and DX stations and that the "entry point" into the path can be some distance from the Tx/Rx aerials then I doubt there can be an accurate solution. I would have thought that the end/start of D-layer absorption in a direction parallel to the terminator should be the start/end of the grayline period for sunset/sunrise respectively. So maybe the concept of a centre is not correct at all. > > -- Joe, K1JT 73 Bill G4WJS. ------------------------------------------------------------------------------ _______________________________________________ wsjt-devel mailing list wsjt-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/wsjt-devel
