1. ATOC 4720: class 3 The distribution of atmospheric mass
The distribution of atmospheric gaseous constituents

2. Previous class
SUM=
0-0.04
325ppm
0-12ppm
5ppm

3. Volcanic eruption Evolution: class
A few percent sulfur & sulfur compounds N2
Evolution: class

4. Questions: How is the mass of the earth’s atmosphere is distributed
Questions: How is the mass of the earth’s atmosphere is distributed? How are various gaseous constituents distributed (both horizontally and vertically?

5. 1. The distribution of atmospheric mass
The earth gravity: so atmosphere has weight --- exerts pressure on the earth’s surface
Newton’s second law of motion:
Atmospheric pressure: the force per unit area
due to the weight of the atmosphere

6. The global mean atmospheric pressure averaged
Over the earth’s surface:
P(0)=

7. Standard atmosphere: the horizonal and
time-averaged strcture of the atmosphere
As a function of height only.
1 Standard atmosphere at the earth’s surface
is 1000mb.

8. Vertical distribution of P, density, mean free path

9. Both Pressure and density decrease with the
Increase of height;
Horizontally, at any given level up to 100km,
the real atmospheric pressure and density are
nearly always within 30% of its “standard
atmoshere.
Vertical variations are much larger than
horizontal changes

10. Since Is
negative
Therefore:

11. Using:
We obtain:
(H=1/2.3B)

12. Similarly,
H=7km.
Half mass of atmosphere: 5.5km
99%: 30km.
Remarkably thin.

13. 2. Atmospheric compositin as a function of height
2 processes:
Molecular diffusion
Mixing due to fluid motion
The level of transition from turbulent
Mixing to molecular diffusion is called
The turbopause. The well mixed region
Below the turbopause is called the
Homosphere; the region above is called
Heterosphere.