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Flashcards in Cloud Deck (40)
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How does cloud form?

Water vapour in the atmosphere condenses into small droplets of liquid water or ice crystals which are suspended in the atmosphere


What are the four general cloud forms?

- Cirrus (threadlike, hairy, fine)
- Cumulus (Heaped or towering)
-Stratus (Sheet or Layer)
-Nimbus (Rain)


How many genera are there?

Genera is the classification of cloud types



How many etages are there?

Etage describes classification of clouds by height



What are etages based off?

Altitude at which the base forms


What altitude does a low etage form?



What altitude does middle etages form?

Between 8500ft and 20000ft


What altitude do high etages form?

Above 20,000ft


High Etage clouds?


- CI: Cirrus ( Fine strands, hooks or clumps of cloud)
-CS: Cirrostratus (A sheet of fine, hairy, wispy or thread like cloud)
-CC: Cirrocumulus (Cirrus forming in elements or lumps)


What are high etage clouds composed of?

- Ice crystals and no precipitation falls from these clouds


What is precipitation?

Rain or hail that reaches the ground


What is Virga?

Rain or hail that doesn't reach the ground


Middle etage clouds?

-AS: Altostratus ( A sheet of middle level cloud, may produce rain or virga)
-AC: Altocumulus ( Heaped or lumpy cloud in middle layer, not usually associated with rain


Low etage clouds?

- CU: Cumulus (Heaped or towering, may produce showers of rain or snow)
-CB: Cumulonimbus (Towering thunderstorm cloud producing heavy showers of rain, hail or snow)
-ST: Stratus (Low sheet of cloud, may produce drizzle)
-SC: Stratocumulus (Sheet of heaped or towering cloud, may produce drizzle)
-NS: Nimbostratus (Sheet of heavy rain, continuous rain or snow


What are the two special form clouds?

- Castellatus


Facts about Castellatus clouds...

- Generally associated with altocumulus
-Appears as a number of turret or cumuliform clouds by a common base
-Indicates instability and may signal later thunderstorm development


Facts about Lenticularis cloud....

- Lens or almond shaped clouds indicating standing wave activity or mountain waves


The type of cloud formed depends on....

- Stability or instability of atmosphere
-Some mechanism which lifts air causing it to cool adiabatically (Due to change in pressure)


How does convection cause clouds?

Warm air rises as a result of surface heating. If conditions are unstable cumuliform cloud will form, perhaps resulting in cumulonimbus cloud if vertical development continues


How does turbulence impact clouds?

Air may be lifted due to surface friction as wind blows over an uneven surface. If condensation occurs an undulating cloud base may form as water condenses in the up currents and evaporates in the down currents


Orographic uplift

As air is forced up over a mountain range it cools adiabatically. The type of cloud formed will depend on the atmospheric stability. if stable conditions exist, stratiform cloud, often nimbostratus (with associated heavy rain) may form. if conditions are unstable, cumuliform clouds will develop


What are mountain waves?

Standing waves generated as orographic uplift forces air up over a mountain range under the following conditions:
-Wind blowing at right angles to the range (Speed increasing with height to at least 25kts at the top of the range)
-Stable layer (An inversion) above the range


If moisture is present lenticular clouds may form on the stationary crests of....

Standing waves


A ragged rotor cloud may be present under the lenticular cloud, in the...

Turbulent rotor zone


What is a front?

When two air masses of different temperatures meet, the warm air will be lifted; the boundary between the two air masses of varying temperature is called a front.


What are fronts usually associated with?

Low pressure systems


What is a cold front?

Cold air moves to undercut warm air and forces it to rise.


A fast moving cold front tends to generate what type of conditions?

Unstable in the air ahead of it; this may result in frontal thunderstorms ahead of the front


How is a cold front depicted on a synoptic chart?

A line with triangles pointing in the direction of movement


A passage of a cold front in the southern hemisphere is marked by:

- Fall in temperature
- Backing of the wind
-A rise in pressure