Most shooters, unless you only shoot indoors, have encountered wind. And probably been relatively irritated by it.
Wind is a bit tricky for a couple of reasons, and not for the reason that it push our pellets/bullets of target.
One is that we are shooting close to the ground and have to deal with wind gradients under roughly 10m (or 10+ yds) of height in flat areas. If it's not flat, i.e. forests, hills, canyons, this rises significantly. What this means is that while you can have 15mph winds at 10yds in one direction, you can have as little as 3mph of wind at 2yds above ground, and in a different direction. So the primary concern we should have is what is the wind in the exact trajectory corridor of the projectile, which we cannot know for certain, because of the way we look and measure the wind. Even if you were allowed the most sensitive equipment invented. You are bound to measure the wind a little lower than the projectile corridor. With the above knowledge you now know that the wind speed is going faster where your bullet is, in relation to where you are reading the wind speed.
The curve is logarithmic, meaning that in theory at least, at zero height above ground (infinite) the wind speed is infact zero. (pressure is not zero though)
So let's for arguments sake say you are measuring 10mph at 10yds in the air, by the the time you are 2yds of the ground that speed has sunk to about 7.5mph, by the time you are 1yds above ground it shrunk to about 6 mph. Keep in mind we are making the assumption that we are on relatively flat ground with few obstructions. Now in our situation we have dont have flat areas....ever. So two things are going to happen, the wind speed in a particular direction will slow down much faster along this curve until it changes direction completely and build speed in a new direction. That is why on some ranges with large structures, berms along the shooting direction, and such, are very hard to shoot in.
This coupled with the other big "forgotten" physical fact that air has mass, and vary depending on barometric pressure and humidity, makes it very tough to accurately predict the wind close to the ground.
Mass I think is easily forgotten when considering wind speed. For example you often hear, the wind just picked up, or just died. And most people will think, ohh it went from X speed to Y speed in an instant. It doesn't, it has mass, and is governed by the same physical laws that dictate that something in motion wants to stay in motion until acted on. This presents a unique problem for us shooters, since the age old way of measuring wind are devices that are free running, i.e. not tensioned or culled. And pr. their design suffer from inertial lag. Example if you have a propeller spinning at 10mph, and the wind picks up or dies down, the delay between the wind and the propeller showing what the wind is actually doing at this slice of time, takes time, and therefore inaccurate by default . That delay length is dictated by inertia and mass of the system, which is why so many shooters that are good at shooting in the wind have spend countless hours and rounds on the range, to learn by experience what the wind flags actually are telling them, and makes judgement calls based on that.
So now "we" have compounded the problem. We know airflow close the ground (under 10yds) is very unstable, yet we use measuring systems that assumes you are above 10 yds (pr. flat ground, calm ocean) to tell us what the wind is doing. Of Course you work with what you have, and some indication is better than no indication. In light steady winds across a range you can estimate fairly well what's going to happen to your trajectory. But as soon as it becomes a little unstable, or shifts direction and or speed, we are in trouble.
There are some spreadsheets out there that let you predict the curve. They are used by, among others, engineers to figure out how tall a windfarm masts needs to be in regards to it's terrain.
Wind is a bit tricky for a couple of reasons, and not for the reason that it push our pellets/bullets of target.
One is that we are shooting close to the ground and have to deal with wind gradients under roughly 10m (or 10+ yds) of height in flat areas. If it's not flat, i.e. forests, hills, canyons, this rises significantly. What this means is that while you can have 15mph winds at 10yds in one direction, you can have as little as 3mph of wind at 2yds above ground, and in a different direction. So the primary concern we should have is what is the wind in the exact trajectory corridor of the projectile, which we cannot know for certain, because of the way we look and measure the wind. Even if you were allowed the most sensitive equipment invented. You are bound to measure the wind a little lower than the projectile corridor. With the above knowledge you now know that the wind speed is going faster where your bullet is, in relation to where you are reading the wind speed.
The curve is logarithmic, meaning that in theory at least, at zero height above ground (infinite) the wind speed is infact zero. (pressure is not zero though)
So let's for arguments sake say you are measuring 10mph at 10yds in the air, by the the time you are 2yds of the ground that speed has sunk to about 7.5mph, by the time you are 1yds above ground it shrunk to about 6 mph. Keep in mind we are making the assumption that we are on relatively flat ground with few obstructions. Now in our situation we have dont have flat areas....ever. So two things are going to happen, the wind speed in a particular direction will slow down much faster along this curve until it changes direction completely and build speed in a new direction. That is why on some ranges with large structures, berms along the shooting direction, and such, are very hard to shoot in.
This coupled with the other big "forgotten" physical fact that air has mass, and vary depending on barometric pressure and humidity, makes it very tough to accurately predict the wind close to the ground.
Mass I think is easily forgotten when considering wind speed. For example you often hear, the wind just picked up, or just died. And most people will think, ohh it went from X speed to Y speed in an instant. It doesn't, it has mass, and is governed by the same physical laws that dictate that something in motion wants to stay in motion until acted on. This presents a unique problem for us shooters, since the age old way of measuring wind are devices that are free running, i.e. not tensioned or culled. And pr. their design suffer from inertial lag. Example if you have a propeller spinning at 10mph, and the wind picks up or dies down, the delay between the wind and the propeller showing what the wind is actually doing at this slice of time, takes time, and therefore inaccurate by default . That delay length is dictated by inertia and mass of the system, which is why so many shooters that are good at shooting in the wind have spend countless hours and rounds on the range, to learn by experience what the wind flags actually are telling them, and makes judgement calls based on that.
So now "we" have compounded the problem. We know airflow close the ground (under 10yds) is very unstable, yet we use measuring systems that assumes you are above 10 yds (pr. flat ground, calm ocean) to tell us what the wind is doing. Of Course you work with what you have, and some indication is better than no indication. In light steady winds across a range you can estimate fairly well what's going to happen to your trajectory. But as soon as it becomes a little unstable, or shifts direction and or speed, we are in trouble.
There are some spreadsheets out there that let you predict the curve. They are used by, among others, engineers to figure out how tall a windfarm masts needs to be in regards to it's terrain.
