1. ATOC 4720 class24 Clouds and storms 1. Extratropical cyclonic storms
2. Artificial modification of clouds and precipitation

2. Previous: Cloud morphology
One type: stratus clouds
Mechanism?
Z: 0-10km (tropopause)
X-Y: hundreds or thousands of square kilometers
10th of hours
A few 10th of g/cm3
Lifting rate: a few cm/s
Often occur in extratropical regions

3. Where is the lifting force from?
In extratropics, this large-scale ascending of warm
air is often associated with the development of cyclones,
which is associated with the approach of a warm (or cold)
front.

4. 1. Extratropical cyclones: cold front and warm front
Occluded front
Cold air
Warm front
Warm
Cold front
Sharp temperature gradient region: front

5. Vertical structure along A-B

6. Vertical structure: both warm and cold fronts lean backward
Warm front

7. Cirrus clouds

8. Cirrostratus: halos

9. Deposition on ice nuclei:
Different from convective clouds

10. 2. Artificial modification of clouds
Cloud microphysics: Warm cloud: collision and coalescence
Cold cloud: deposition and then
riming and aggregation
According to these ideas: modify clouds:
Seeding: introduce hygroscopic particles or water drops in warm
clouds;
Seeding: artificial ice nuclei into cold clouds (1/liter)
Introduce relatively high concentration of artificial ice nuclei
into cold clouds (to reduce the concentration of supercooled
water and therefore inhibit the growth)

11. Dry ice (-78C: more efficient in dissipating
clouds)
Silver iodide (-10C)

12. Artificial modification of Precipitation

13. Evaluation
Physical
Statistical