James observations tie in with my own. We now have a weather station at home and the measured humidity did not directly tally with bad air days but cold, foggy still days are a near racing certainty for a drop off in distance. When you dig in to surface level atmospheric behaviour, factors such as terrain, radiation, advection, and subsidence all play a role and it is very difficult to pin down a single factor for the onset of these conditions, except that you know when you are in it.James9118 wrote: ↑Thu Nov 30, 2023 9:18 am I discussed this on a number of occasions with Vince, who found the reference he posted above, showing that drag can be significantly reduced if the approaching airflow is turbulent.
As such, I think the 'distance falls in high humidity' observation has some truth in it, but it's not simply a result of the humidity which, as you rightly point out, would actually lower drag. I suspect observations of poor distances in sticky, high humidity conditions are more linked with lack of wind and perhaps a transition to a more laminar flow.
regards
Vince
PS I just dug into some of the historic discussion with James on the topic and lifted this quote which is probably relevant "In the atmosphere, moisture, and particularly condensed moisture, strongly modulates the emission, absorption, and reflection of radiant streams of energy, and this in turn helps determine the rate that radiative processes stabilize or destabilize the flow".