How does the atmosphere work?

[InfiniteNow]

Would cloud be formed at normal height when it is foggy? What causes the fog to occur at ground level?

 

Also, why is it when it's really cold at night, the sky conditions are perfect for astronomy? The sky is always perfect when the temp. is ultra cold.

:)

 

The point of this thread was to discuss friction of objects passing through the Earth's atmosphere from space. Please open a new thread, or perhaps more ideally, check out google and/or wiki. They are your friends. :)

 

 

 

 

Fog - Wikipedia, the free encyclopedia

Cloud - Wikipedia, the free encyclopedia

[LJP07]

I didn't think it was off-topic becuase the title asks " How does the Atmosphere work " and the original question was already answered. Didn't think that was against the rules. Anyhow I also thought that if small questions were answered such as this a lot of little threads would appear without any real chat thus making too many threads. This thread should serve as a title for all these little atmospheric questions, do you not agree? :)

[InfiniteNow]

Would cloud be formed at normal height when it is foggy? What causes the fog to occur at ground level?

Whatever, I'm bored.

 

Air temperature varies with altitude. Fog/clouds occur when are temperature cools to the dew point temperature. If the altitude at which air temperature meets dew point temperature is closer to ground level, viola... fog is born. If this happens higher up, we just call it a cloud.

 

Six to one, half a dozen to another...

 

Also, why is it when it's really cold at night, the sky conditions are perfect for astronomy? The sky is always perfect when the temp. is ultra cold.

 

There is not one single parameter (such as surface weather, mesoscale products, or vertical atmospheric profiles... just think "turbulence" and you'll get a better grasp) that influences optimal days for astronomical viewing. They all come together to make good/bad viewing. If I were to guess, I'd suggest that cooler air is less turbulent.

[cwes99_03]

The couple of questions asked here.

 

I too was under the impression that Turtle was correct, that it is due to the compression of gas molecules that heating occurs. Isn't this phenomena and friction related to the same principles of particle interaction? The ideal gas law says that the temperature will rise with an increase in pressure and no reflexive increase in volume (for a closed energy system). This most certainly occurs on the leading face of an object entering the atmosphere and for that matter on every type of windfoil. The same principle is true of any type of molecular fluid (is it true of electron gasses as well? i think so). Thus water being compressed at higher and higher pressure without the corresponding change in volume will also increase in temperature, but not along the same curve as the ideal gas law (as water does not behave like an ideal gas).

 

So with all those thoughts, I turned to the web and found this from columbia's free online dictionary under the topic ideal fluid.

 

The ratio of the shearing stress to the velocity gradient is a measure of the viscosity of the fluid and is called the coefficient of viscosity η, or η=Fx/Av. The cgs unit for measuring the coefficient of viscosity is the poise. Experiments have shown that the coefficient of viscosity of liquids decreases with increasing temperature, while the coefficient of viscosity of gases increases with increasing temperature. In liquids an increase in temperature is associated with the weakening of bonds between molecules; since these bonds contribute to viscosity, the coefficient is decreased. On the other hand, intermolecular forces in gases are not as important a factor in viscosity as collisions between the molecules, and an increase in temperature increases the number of collisions, thus increasing the coefficient of viscosity. A striking result of the kinetic theory of gases is that the viscosity of a gas is independent of the density of a gas. Viscosity is the principal factor resisting motion in laminar flow. However, when the velocity has increased to the point at which the flow becomes turbulent, pressure differences resulting from eddy currents rather than viscosity provide the major resistance to motion.

 

Basically from my past 45 minutes of reading it is actually both. Turbulent flow heat flux is set up by the massive differences in pressure and velocity of the gasses surrounding the entry vehicle.

 

Now as to whether or not the impact at say 200 mph with a dense liquid can be compared to impact with a concrete wall. Yes. Note however when one says this they are simply comparing the impact force or sudden deceleration. They are not saying that if one were to jump from a plane and land without parachute that the effects of hitting water and hitting concrete would be equal. Not at all. The effects would be similar to hitting concrete at a much lower velocity.

That is to say, in the first inch or so of water that you collide with, your body will slow down from 200 mph to (just a guess here) 150. This -50mph acceleration is the same as what you would feel if you ran into a concrete wall at 50 mph (given that your body could easily compress an inch when colliding at such a speed.)

 

As to the fog, the density has to do with the supersaturation coefficients of the mixture of gasses and temperature of the air. There is some pretty complex pchem when it is all said and done. That's why nimbus clouds generally form at certain elevations and what not. Cirrus clouds are actually clouds of ice crystals. Fog is most similar to cumulous clouds.