ATOC 4720 class20

• Clouds and storms

1. Cloud morphology

2. Types of clouds

3. The air-mass thunderstorm

ATOC 4720 class20

Thermoelectric effect in ice:

T- degree C; V--mV

From class-19:

[1]

[2] Supercooled water in clouds

3. Lightning and thunder

Dielectric breakdown: V>3MV/m (dry) V>1MV/m Moist with 1mm in radius;

Class-19:

Lightning: T--30,000K;Thunder: Shock waves;

1. Cloud morphology

Clouds: Mechanisms of formation [1] Convective clouds: local ascent of warm, conditionally unstable air; 0.1-10km in diameters; Vertical velocity w: a few m/s; Liquid water or ice content:

[2] Layer clouds: stratus

Forced lifting of stable air:

Examples: fog is forced lifted upwards; cold fronts lift warm air massHundres--thousands km; Lifting rates: a few cm/s;Water: a few tens

Tens of hours

stratus

[3] Orographic clouds

Forced lifting of air by hills or mountains

Uplifting velocity depends on windspeed and direction,And mountain height. Can be a few m/s;Water: a few tens

Can be transitory, or can stay for long if winds are Steady.

http://www.faa.gov/and/AC0057/AC0057.HTM

Lee waves can also produce orographic clouds;

Orographic clouds

[4] Advection fog:

Cooling of air below its dew point due to warm air is Advected to a colder surface.

Fog

[5] Arctic sea-smoke (steam fog) Meeting of two parcels of air with different temperatures; both close to be saturated.

Arctic sea-smoke

[6] Funnel clouds

Adiabatic expansion and cooling due to a rapid local Reduction in pressure.

Tornadoes or water spouts.

Funnel clouds

Funnel clouds

[7] Instabilities (Kelvin-Helmholtz instabilities)

Strong wind-shear modify cloud shape;

Billow clouds: K-H instability

Types of clouds

Many types: (International cloud Atlas)

Cumulus: StratusCirrusNimbus(combination) Cirrostratus

Cumulus

Cumulus tower

Cumulonimbus

Stratus

Cirrus clouds

Cirrostratus: halos