UNIT 9 Flashcards
Cloud
Visible masses of suspended, minute water droplets and or ice crystals
Cloud formation ingredients
moisture, rising motion, condensation nuclei
Classify clouds based on..
height and shape
cirrus
thin; wispy cloud; composed of ice crystals; typically found at higher levels (above 6 km)
stratus
Flat layered appearance, fairly thin, and cover a large region
- low: stratus; below 3km (10,000 ft) - middle: altostratus; 3-6 km (10,000-20,000 ft) - upper: Cirrostratus; above 6 km
nimbostratus
low level thin cloud; rain producing
cumulonimbus
very tall cumulus clouds, anvil shaped top, violent weather; extends from 500 m to 12 km
cumulus
Thick, puffy masses that often develop to great heights
- Low: Cumulus/ stratocumulus; (Below 3 km) - Middle: altocumulus; (3-6 km) - Upper: cirrocumulus; (above 6 Km)
Mammatus Clouds
usually associated with severe weather and hail
Lenticular Clouds
found on top of mountains
Kevin-Helmholtz clouds
wave like appearance; turbulence
Contrails
help block sun radiation and prevent long wave radiation from escaping at night
Fog
visible masses of suspended, minute water droplets and or ice crystals; very near to the ground; NEEDS MOISTURE AND CONDENSATION NUCLEI
Does fog form adiabatically or diabatically?
diabatically; air reached saturation through contact with cold air or exchanges of sensible heat with a colder surface( supports less moisture)
radiation fog
occurs as the surface loses its heat to space; the air near the ground cools; water vapor condenses; most common type, generally occurring on clear, cool nights; thickets before dawn
Advection Fog
Warm moist air advects over cold surface and cools to dew point; common near oceans; can be found over snow-covered grounds; thicker band more persistent; ex: San Francisco (Advection is horizontal transport of something)
steam fog
cool air moves over warm water, producing enough moisture to saturate the air above it
DEW
visible masses of minute water droplets; water droplets on the surface. NEEDS MOISTURE AND CONDENSATION NUCLEI & FORMS DIABATICALLY
precipitation
falling water/ice from the sky
rain
precipitation that falls when temperature is above freezing
sleet
partially melted snowflake that refreezes before it hits the ground
snow
ice crystals that fall through atmosphere and do not encounter any layers above freezing temperatures
freezing rain
precipitation that falls as rain, but freezes when it comes in contact with sub- freezing surface
hail
precipitation that forms ice crystals are blown about within a tall and very moist cloud; NEEDS MOISTURE, CONDENSATION NUCLEI, AND RISING MOTION
If you get enough moisture droplets, they collide and combine and grow in size which causes them to fall out of the sky; all precipitation originates from parcels of moist air rising (cooling adiabatically)
know this!
Air mass thunderstorms
- a very large individual towering cumulonimbus
- don’t last long
- move slow
- need maritime tropical air mass
Air mass thunderstorms form when…
- moisture
- rising motion
- condensation nuclei
- weak winds aloft (keep storm perfectly vertical)
- Updraft is warm and downdraft is cold air; rain creates downdraft
The Life Cycle of an air mass thunderstorm
- cumulus (developing stage): only an updraft because you must build the cloud; is NO DOWNDRAFT
- mature: updraft continues while cloud builds; heavy rain begins to fall producing a downdraft of cold air because they come from high levels of troposphere
- dissipating: downdraft dominates weakening the updraft, moist air; system “suffocates”
SEVERE THUNDERSTORM (only need one of these conditions)
- must have a surface wind gust of 58 mph or greater
- hail 1 inch or greater in diameter
- produces a tornado
severe thunderstorms form when…
- moisture
- rising motion
- condensation nuclei
- vertical wind shear
vertical wind shear
want wind to change in speed and direction with height; the updraft gets tilted and it no longer interferes with downdrafts
Squall Line
occurs when individual severe thunderstorms 1-5 miles wide become arranged in a line; typically form in front of COLD FRONT
Mesoscale convective complex
form when multiple single thunderstorms converge together; the storms feed off of one another
Supercell
individual thunderstorms that assume their own rotation; most dangerous type
Lightning and Thunder
- Lightening is an electric discharge from a thunderstorm based on charge differences in the atmosphere (positive at the top and negative at the bottom)
- Thunder produced by rapid expansion of air by lightning bolt
Hail
- precipitation phenomena
- ice crystals pass thorough subfreezing and above freezing layers collecting water
- hail will take a layered appearance: clear vs. opaque
- When a hailstone is high in the troposphere freezing very quick and traps air bubbles which makes the layer of ice opaque
- When a hailstone is at the bottom of a cloud, it freezes at a slower rate and air bubbles are allowed out making it clear
- once hail gets large enough, the updraft cannot support it allowing it to fall
Tornado
- small vortex of air
- associated with low pressure
- Descends from the wall cloud at the base of the thunderstorm
- winds can range from 110mph-200+
- tend to see tornadoes in May and June; there needs to be a clashing of air masses
