Download Lecture 20

ATOC 4720 class20
• Clouds and storms
1. Cloud morphology
2. Types of clouds
3. The air-mass thunderstorm
From class-19:
[1]
Thermoelectric effect in ice:
T- degree C; V--mV
[2]
Supercooled water in clouds
Class-19:
3. Lightning and thunder
Dielectric breakdown: V>3MV/m (dry) V>1MV/m
Moist with 1mm in radius;
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 mass
Hundres--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.
Lee waves can also produce orographic clouds;
http://www.faa.gov/and/AC0057/AC0057.HTM
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:
Stratus
Cirrus
Nimbus
(combination) Cirrostratus
Cumulus
Cumulus tower
Cumulonimbus
Stratus
Cirrus clouds
Cirrostratus: halos