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ATOC 4720 class24
• Clouds and storms
1. Extratropical cyclonic storms
2. Artificial modification of clouds
and precipitation
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
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.
1. Extratropical cyclones: cold
front and warm front
Occluded front
Cold air
Warm front
Warm
Cold front
Sharp temperature gradient region: front
Vertical structure along A-B
A
B
Vertical structure: both warm and
cold fronts lean backward
Cold front
Warm front
• Cirrus clouds
Cirrostratus: halos
Deposition on ice nuclei:
Different from convective clouds
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:
1. Seeding: introduce hygroscopic particles or water drops in warm
clouds;
2. Seeding: artificial ice nuclei into cold clouds (1/liter)
3. Introduce relatively high concentration of artificial ice nuclei
into cold clouds (to reduce the concentration of supercooled
water and therefore inhibit the growth)
Dry ice (-78C: more efficient in dissipating
clouds)
Silver iodide (-10C)
Artificial modification of
Precipitation
Evaluation
• Physical
• Statistical