why do we feel turbulence in an aircraft when going through clouds formed in the air, but not when walking through clouds formed at the surface?
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You don’t have hundreds of m^2 surface area or travel at hundreds of miles an hour. The same air disturbance that feels like a breeze to a person is a strong force on a flying plane.
A better example would be swimming in an inlet to the ocean. You can feel the interacting water currents much more strongly than you can air at a human scale.
airplanes move fast, like 700km/h-900km/h fast. moving that fast means crashing into and displacing a huge mass of air (and water vapor, if there are clouds), and that’s what causes turbulence.
us walking still displaces the air in front of us, but not fast enough that it becomes a problem.
Because it is often the movement of air vertically that creates clouds in the air.
The clouds formed on the ground are far less dynamic.
And there’s the fact you’re not supported by the air when you’re walking on the ground. If the air density suddenly changes it doesn’t affect what’s holding you up.
Turbulent drag is proportional to speed squared (as opposed to laminar drag which is proportional to speed). The faster you move, the more severe the turbulent force is.
Example. Hold your hand out while walking. The air resistance on your hand is pretty much negligible. Now if you stuck your hand out the window in a car while driving 60 mph, you will notice the air resistance on your hand to be much stronger.
Clouds create regions of high and low density air which creates the turbulence as you pass through it.
Turbulence is caused by a change in the airflow around the wings, not by the clouds themselves. Normally, the air going over the wings exhibits what is called laminar flow. Laminar flow is nice and smooth, and different layers of air moving different speeds don’t interact with each other. Laminar flow is super cool, and is responsible for some really cool fountains. Google it!
Turbulance is caused by the disruption on the neat, ordered laminar flow and an appearance of turbulent flow (that’s really what it’s called). This temporary changes the lift dynamics of the wing, and you feel turbulance.
We do feel turbulence on the ground, it’s called wind gusts. Have you ever driven a truck or van in a strong crosswind?
Aircraft are exposed to winds moving up and down as well as sideways, and the extra surface area of wings lets you feel the acceleration more strongly. They can also move from a region of air with wind consistently moving in one direction, to a region of air with the wind consistently moving in a different direction, you’ll feel a jerk when you make that transition.
On the ground we have an anchoring point at our feet from which we can counter gusts of wind (eg people walking into a strong wind will naturally lean forward more than usual as they walk). It’s like how if you wade in a river you won’t get pushed along unless there’s an especially strong current, but if you float on it or tread water you’ll most likely drift.
It’s also worth noting that humans do not come in very aerodynamic shapes. Planes on the hand are designed specifically to catch the air around them. If you’ve seen someone’s umbrella fly off on a windy day or even just a newspaper flapping around, that’s probably a better indication. Also, if you’re talking about in clouds specifically, most of the time clouds/mist/fog only gather at surface level when it’s relatively not windy – in strong winds they normally dissipate very quickly unless you’re up a mountain or something like that.
Simply passing through ‘normal’ clouds such as on descent gives us a sense of ‘buffeting’ in the plane, but it is not truly the same as turbulence in the air.
Air with saturated water vapour in it (i.e. clouds) is less dense than drier air. A plane flying at high speed entering a cloud suddenly transitions to less dense medium. This reduces both the drag AND the lift on the plane and so is like a ‘jolting’ of the plane by changing outside forces. The effects are relatively small – as we know – the plane emerges unscathed and we just feel low scale bumps.
Clear air turbulence and also in clouds such as towering cumulonimbus (thunder clouds) are different phenomena and can cause the more violent turbulence that we hopefully rarely experience.
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