Thanks for all the links and

[Nick James]

Thanks for all the links and references. I hadn’t realised that the Solar atmospheric “tides” were actually thermal rather than gravitational unlike the lunar one which is definitely gravitational or that the solar tides lead to small (mm) deformations in the solid body of the earth. Yet another small cause of the increase in day length. Anyway, I have a big dataset and will write some code to do a proper analysis of this for the sun and moon and see what I can find.