I've seen a similar type of ducting when there was no skywave propagation at all but at the seafront signals were coming in from other coastal stations well out of range of normal line of sight but usually a very steady signal strength on one day for hours on end which just suddenly disappears,I wasn't only one witnessing it either as a boat en route from Scotland heading to N.Ireland was getting it too,the station we were both getting was on Blackpool promenade,well into the North of England and far from the seafront of the town of Saltcoats on the clyde estuary but we couldn't get through as I didn't have amp with me and he was being bombarded by Rep of Ireland stations directly across the irish sea from him,but I had him S2 for over 4 hours.I call it sea ducting, not sure if anyone else has come across this phenomenom
absolutely come across that phenomenom. FN30 here, home is less then 2000' from the atlantic ocean, & frequently mobile in a parking lot or on the beach literally on the edge of the atlantic ocean. it happens most often early morning, but can happen any time of day, any season, any weather. but you cannot plan on it. it just happens. sometimes for minutes, sometimes for hours, sometimes it slowly fades away, sometimes it just disappears. sometimes it's only directly across water yet other times it goes well inland, or across water then inland....VA, MD, DE, NJ, RI , and across long island sound then up to east coast of MA & even nova scotia has been contacted when ther is no other apparent propagation. sometimes just a few hundred feet is the difference in S9 or nothing. i've heard stuff from home, ran out in the mobile to find signals disappear as i drive down the street, non-existant at the waterfront, only to return home & find the statio still out there.