What is the theory of a raindrop?

[mersecske]

What is the theory of a raindrop?

What kind of effects influence its size?
I think that the size is increasing due to the smaller drops (spray)
But what about evaporation, because the drop has large velocity

 

[Danger]

As to size, I'd think that the primary deciding factors are surface tension vs. external stresses such as g force and air resistance.

 

[NobodySpecial]

I would have thought the maximum size was set by the time it had to form.
Bigger than a certain size it's going to fall, unless there is an up draught to hold it then it's going to fall as rain before it has time to grow

 

[Bob S]

If a raindrop falls through a uniform density fog, collecting the mist and increasing its size (collecting mass from the region it traverses and neglecting evaporation and air drag) from rest at zero radius as it falls, it will fall with a constant downward acceleration less than g. (Related to problem 8-22 in Becker "Introduction to Theoretical Mechanics."

Bob S

 

[mersecske]

Why can we neglect evaporation?

 

[Bob S]

If the relative humidity approaches 100% (as in a fog), the evaporation rate reduces to zero. See

http://www.Newton.dep.anl.gov/askasci/wea00/wea00063.htm

Bob S

 

[Dr Lots-o'watts]

Why can we neglect evaporation?

Because in humid air, it collects much more water than it evaporates.

If there is more evaporation, then it's certainly not raining.

 

[Bob S]

Virga is a type of rain shower over very low humidity desert areas where the raindrops completely evaporate before hitting the ground.

Bob S

 

[mersecske]

Thanks, so both effects are important. Are there any other effects? For example temperature changing?

 

[Danger]

Virga is a type of rain shower over very low humidity desert areas where the raindrops completely evaporate before hitting the ground.

Bob S

Just to clarify, it doesn't have to be a desert. Such occurs here in Alberta on a regular basis.