As many shooters know, as distance increases, wind calling is increasingly difficult in warmer temperatures.
How much of a difference is there in wind drift between, say, 10 and 0 degrees Celsius? Or any other usual temperature difference -- e.g. between 20 and 0 degrees Celsius?
For sure wind calling is increasingly difficult with distance. I am not sure about the temperature assumptions for the dynamics.
From my recent readings (where I may have misunderstood things), drag increases as air density increases, and air density increases as it gets colder (at a given altitude).
However I am not a physicist, and so I stand to be corrected on everything ballistics-wise.
I am most interested in this topic for how my wind calls at 50m and 100m may be affected in the winter months. We have heated shooting houses at my local range and so we can shoot rimfire all winter long without freezing our fingers and bodies (for which I am most grateful!). My brain tries to calibrate on wind flags in matches for holds, but what if I have to change the calibration as the air temperature changes from -30C to +30C, which is the 60 degrees of air density changes I shoot in all year round? I don't know the answer. Some clues follow:
Wikipedia article: External Ballistics:
https://en.wikipedia.org/wiki/External_ballistics
It states: "Wind has a range of effects, the first being the effect of making the projectile deviate to the side (horizontal deflection). From a scientific perspective,
the "wind pushing on the side of the projectile" is not what causes horizontal wind drift. What causes wind drift is drag. Drag makes the projectile turn into the wind, much like a weather vane, keeping the centre of air pressure on its nose. This causes the nose to be cocked (from your perspective) into the wind, the base is cocked (from your perspective) "downwind." So, (again from your perspective), the drag is pushing the projectile downwind in a nose to tail direction."
Wikipedia article: Density of air:
https://en.wikipedia.org/wiki/Density_of_air
This article has a handy chart showing how air density increases as the temperature decreases.
Wikipedia: Drag (physics): Drag equations is where everything comes together for understanding the wind forces on the bullet.
https://en.wikipedia.org/wiki/Drag_(physics)
The drag equation is:
Fd = 1/2 pv^2 CDA
where:
Fd is the drag force,
p is the density of the fluid (in this case air),
v is the speed of the object relative to the fluid (^2 is the velocity squared)
A is the cross sectional area, and
Cd is the drag coefficient
As we see, as air density (p) increases, its will increase the force of drag on the bullet.
Since wind is acting on the drag force, I concluded (maybe incorrectly), that as the drag force increases as temperature decreases, then a given wind velocity would exert more drag force as air temperature decreases. Hence, shooting conditions in the wind are tougher the colder the air gets? (if I understand all of the above, which I may not).
However, for aircraft and missiles travelling at high altitudes and through a wide cross section of altitudes, ballistics gets very much more complex because air density decreases with increasing altitude, even though air temperature at high altitudes gets colder as altitude increases.
(Aside: Interestingly in my reading, contrary to my former belief, I found that at our normal shooting altitudes, increasing relative humidity
decreases air density. Dry air is denser than humid air at a given temperature and altitude, and therefore drag increases as the air gets less humid).
