1. ATOC 4720: class 4 Variable constituents
Charged particles in the atmosphere

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

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

4. Atmospheric composition 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.

5. 1. Variable constituents

6. Atmospheree composition
SUM=
0-0.04
325ppm
0-12ppm
5ppm

7. Water vapor: sources and sinks

8. Main source: evaporation from the earth’s surface is the main source of atmospheric water vapor;
Condensation which takes place in clouds is the main sink of atmospheric water vapor.
Typical “lifetime” of a molecule of water vapor in the atmosphere is only “a week”.
Concentration:

9. Ozone: source and sink

10. Source: Ozone is primarily generated by photochemical reactions in the layer between km; [polluted air: small]
Sink: At the earth’s surface, reaction with plants and dissolving in water.
At km, it is rather stable with a lifetime on the order of months.
Long-term average, downward ozone flux

11. 2. Charged particles in the atmosphere
Importance: play a crucial role in geophysical phenomena: lightening, reflection of radio waves, fluctuations in the geomagnetic field, etc.
Sources: (1) X-ray and UV radiation from the sun ionizes air molecules. All the sun’s ionizing radiation is absorbed above 60km; (2) High-energy cosmic rays; (3) Radioactive decay within the earth’s crust; (4) Electric charges: separated within clouds.

12. Most electrons: >60km