Humidity, Air Conditions and Casting

[VGB]

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.

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.

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".

[Stoatstail50]

Less lift in the loop.

[James9118]

Less lift in the loop.

Pixies don't like sticky, hot conditions so they find somewhere else with a cooling breeze.

[Walter]

Another thing I’ve wondered about is whether size matters.

By that I mean the difference between comparing larger bodies like airplane wings to fly line cross sections. Airplanes and other large bodies consistently report the expected effects of lowered drag in higher humidity and are less affected by the lack of turbulence and fly lines are more significantly affected by the turbulence factor?

Lasse:

I think there is also a psychological factor as well. Pole vaulters and long jumpers, for example, can feel cramped in when moving from an outdoor venue to an indoor venue and that affects their performance. Most of them adjust to it over time but the adjustment period will vary between athletes.

[Walter]

Less lift in the loop.

2 mm instead of 3?

[VGB]

Another thing I’ve wondered about is whether size matters.

By that I mean the difference between comparing larger bodies like airplane wings to fly line cross sections. Airplanes and other large bodies consistently report the expected effects of lowered drag in higher humidity and are less affected by the lack of turbulence and fly lines are more significantly affected by the turbulence factor?

Reynolds numbers deal with the scaling issues. I’m not sure that the issue with aircraft is so much less drag as more thrust at lower temperatures due to increased density.

Regards

Vince

[Walter]

Pixies don't like sticky, hot conditions so they find somewhere else with a cooling breeze.

Sounds like a quantum effect.

[Paul Arden]

I don’t think it’s psychological Walter. Not after ten years! It’s significant and about 10 feet. Maybe it’s not humidity that’s the cause. Here we tend to blame Hantu Tetek when things don’t go according to plan.

Cheers, Paul

[VGB]

I think that there’s been a tendency to fixate on humidity because it is an easily measurable property. Humidity in isolation may be a bit of a red herring as far as drag is concerned. It has been around 35% for the last couple of days and casting is hard. During the summer, it was hitting 75-80% and casting was a pleasure, I hit my best distances and carries because there was usually a light breeze and probably resultant turbulence.

Being on an island, we are often subjected to sea-land breezes on a diurnal cycle. We tend to lose that breeze when land and sea temperatures equalise, usually in the morning and evening, resulting in mist and fog.

There are many different types of fog based on the factors I mentioned at Post 11; terrain, radiation, advection, and subsidence

https://www.metoffice.gov.uk/weather/le ... pes-of-fog

I was casting in either evaporation or radiation fog yesterday that hung on because of the sharp changes in air temperatures. Both cause the still air that has high relative humidity to lose temperature and pressure. Consequently, the water condenses from gas and the resultant loss of volume further reduces pressure. Valley fog is probably similar but not an issue around my area, maybe James sees it?

If you get the same effect on casting in tropical areas it is likely be due to the factors James mentioned but advection is a possible culprit, as is subsidence. However, it’s a bit of guesswork because we don’t often get tropical conditions in the UK

Regards

Vince

[Lasse Karlsson]

I don’t think it’s psychological Walter. Not after ten years! It’s significant and about 10 feet. Maybe it’s not humidity that’s the cause. Here we tend to blame Hantu Tetek when things don’t go according to plan.

Cheers, Paul

How far can you cast in a real flat calm? Or indoors?

Cheers
Lasse