Now i know where the lightning comes from.
Seems as if the track uses the skybox from Neil Faichney.
It uses a nightlight for the illumination of the horizon:
So just delete the following lines in the *.scn file (or set two slashes in front of each of the 4 lines to deactivate them):
Light=NightLight00 // used only to activate horizon town light effect
{
Type=Omni Pos=(-223.159912, 11.439373, 12.055908) Range=(0.000000, 1.000000) Active=True
}