Cumulonimbus formation

[jones123]

Hi,

 

my textbook has given the following weather sounding as a typical formation of a cumulonimbus (thunderstorm) cloud. But I don't really understand why this can happen on this figure. The LCL is situated left of the environmental temperature (red curve) so actually, the air parcel should stop rising in the middle between the LCL arrow and the Γ = Γd arrow (since it's in a stable layer) right? So i see this as a situation where no clouds can form.

Can someone confirm this or explain why I'm wrong?

Thanks!

[Enthalpy]

Mine will be a more general answer not based on the supplied graph - sorry for that.

 

As warmer air rises because the atmosphere's temperature gradient with altitude is big enough, it reaches a height (unless exceptionally dry) where the contained vapour condenses.

 

The resulting dense liquid water droplets make air more dense than light vapour does, but vapour's condensation heat also let the containing air cool less, and this tends to make the air bubble lighter than the surrounding.

 

When the first effect (liquid water dense) outweighs, the air bubble gets quickly denser than its surrounding. It produces a cumulus, whose base is flat (=condensation altitude), and the ascension stops.

 

When the second effect (vapour condensation keeps air warm) outweighs, the air bubble stays lighter than the surrounding air, or even, gets increasingly lighter than the surrounding, and produces a cumulo-nimbus where the bubble loaded with liquid water continus to rise, up to the stratosphere's base where the tropospheric temperature gradient stops.

 

The typical conditions for cumulo-nimus is a cold front, where denser cold air moving forward tops lighter air kept back by the ground. The abnormally denser surrounding air helps the rise of the bubble.

[Essay]

I'm going to enjoy this .pdf more fully, later, when I have some free time.

 

http://envsci.rutgers.edu/~lintner/tropmet/Lecture8.pdf

 

But, if you could ask questions relative to the .pdf, it might be easier to narrow in on specific answers... if you don't see how that part of cloud formation occurs, from this link.

 

~

[EdEarl]

LNB, LCL, LFC, LI, a.g.l, cste, q, and gamma?