ATOC 4720 class 24 Clouds and storms 1

ATOC 4720 class 24 • Clouds and storms 1. Extratropical cyclonic storms 2. Artificial modification of clouds and precipitation

Previous: Cloud morphology One type: stratus clouds Mechanism? Z: 0 -10 km (tropopause) X-Y: hundreds or thousands of square kilometers 10 th of hours A few 10 th of g/cm 3 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 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 2. clouds; 2. Seeding: artificial ice nuclei into cold clouds (1/liter) 3. Introduce relatively high concentration of artificial ice nuclei 4. into cold clouds (to reduce the concentration of supercooled 5. water and therefore inhibit the growth)

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

Artificial modification of Precipitation

Evaluation • Physical • Statistical