I don't think I ever gave details in this topic of the reason I originally asked the question. Austwick Beck Head has been extended this year, mainly by diving. Sump 1 is short and in dry weather there is a thin airspace. There has been an inward draught here right through the warmer months of 2021. But there should have been an outward draught in hot weather, if ABH is the lowest entrance of the system it drains. (Sump 2 beyond is never unroofed and the draught goes into a choked bedding above water between the sumps, which is yet to be investigated properly. Sump 1 is not safely passable without diving gear by the way, as the route through involves complete submersion, whether or not airspace exists, via a couple of awkward restrictions.)
There must be another entrance which is low enough to generate a convectional draught. Contenders include Blind Beck Cave (22 m lower) and Beck Head Stream Cave (32 m lower). BBC has a feint outward draught in warm weather; BHSC has a strong outward draught. Could either of these two air currents originate from ABH?
Being able to trace such draughts, in the manner of tracing water, would be a very useful technique to develop for cavers generally. Maybe a BCRA field day, bringing folk together who are interested, might be of value?