Asymmetrical AM (Amplitude Modulation).

[Mike Watterson]

As for adaptive carrier power, won't that give rise to audio compression in receivers with AGC? (Or is is just not very noticeable?)

I think The defunct since April 2023 RTE1 on 252 kHz used it and I think R4 on 198 kHz uses it, if so it's not noticeable.

I used to listen in to LW a bit in the Library, but the only serious LW listening I've done in last 20 years is in the car where some compression helps! I swapped the stock radio in my 2008 Yaris this year so as to have decent R4 LW. Some work with cutters, Dremel etc needed on removable facia. Adaptor to standard connections via cutting an old adaptor and cutting off end of existing cables and screw terminal blocks. At least aerial plug was the same kind and the old radio mount to car chassis plates amazingly fitted. Also now I get a 3.5mm audio in. Kenwood with VFD display, though display goes into "demo" mode and you have to hit a button. Some day I'll look for a manual.

Does it cause audio compression on sets with AGC? Which is nearly all. There was maybe a couple of Ever Ready 1950s battery valve sets with no obvious AGC at all, not even on the DK96 (apart from pre-1934 sets I have). I think it would depend on the AGC time constant and algorithm for adjusting TX carrier power. Any compressor in the TX / Studio audio path will have more effect?

Also how much is carrier power varied vs whatever local gain the AGC action has, which might have some compression action on long time constant even on conventional AM?

Too many known unknowns and some unknown unknowns and too few known knowns on too many different radio designs.