On Dec 13, 8:59 am, Paul Hyett wrote:
I can understand why low pressure cells are deeper in winter - greater
temperature contrast, but what mechanism causes winter high pressure
cells to have higher central values than summer ones?

Short answer is that cold air is denser. So total column density is
larger. Clear skies of a high with limited hours of winter insolation
tend to allow the nights to be colder and self reinforcing. The sun is
very low in the sky this time of year.

It is a very cold frosty day with bright azure blue sky and golden
sunshine up here in N Yorks today.

Regards,
Martin Brown