These data are from a single dipole. So, it might be coupling between that and other dipoles, or perhaps Cas A rippling through a sidelobe. For the UK station (which doesn't see the effect -- REF), these sources would be at different position angles. There are several things we have now checked:
We see it on different dipoles. These might have different couplings (due to antenna spacings) or be at different position angles (with respect to, say, a local RFI source).
We also see it on both polarisations. The following two plots are from different polarisations.
|LBA aerial #L04, X-polarisation (Image: D. McKay-Bukowski)|
|LBA aerial #L04, Y-polarisation (Image: D. McKay-Bukowski)|
We may still be seeing some sort of ground effect or perhaps a reflection from the reindeer fence. Alternatively, it might be a "snow interferometer" (like the old sea-interferometer, but with a reflection off the snow). The fact is that the sun is at quite a low elevation and the wavelengths are quite long at these frequency bands.
In any case, we remain puzzled. Any suggestions, anyone?