In rec.radio.amateur.antenna Spike wrote:
On 07/12/2015 08:22, Ian Jackson wrote:

BBC Radio 4 on 198kHz is receivable (weakly) in Malta (900 miles?). It's
definitely stronger at night. Why is that?

It's jimp's newly-invented variable ground wave.

All propagation modes are variable over time due to a number of reasons.

--
Jim Pennino