Cloud Flashcards
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
10
How many etages are there?
Etage describes classification of clouds by height
3
What are etages based off?
Altitude at which the base forms
What altitude does a low etage form?
8500ft
What altitude does middle etages form?
Between 8500ft and 20000ft
What altitude do high etages form?
Above 20,000ft
High Etage clouds?
Types…
- 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
- Lenticularis
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
When warm air replaces cold air, the boundary is known as….
A warm front
What happens in a warm front?
Warm air rides up over the cold air forming a boundary sloping in the direction of movement. The warm air is generally stable resulting in stratiform clouds, with rain from nimbostratus
How is a warm front depicted on a synoptic chart?
Solid line with semi circles pointing in the direction of movement.
What would indicate the approach of a warm front?
High level cloud, followed by mid level cloud and eventually extensive nimbostratus
The passage of warm front is marked by…
- Rise in temperature
- Backing of wind
- The pressure fall decreasing
What is an occluded front?
A cold front which has caught up to a warm front
How is an occluded front represented on synoptic chart?
Circles and triangles pointing in same direction on line.
What is the weather associated with an occluded front?
Both warm and cold front type weather, often with extensive cloud and widespread rain
What is an Quasi-stationary front?
Warm and Cold front meet from different directions
How is a Quasi-stationary front represented on synoptic chart?
Triangles and circles pointing in opposite directions of line
