Clouds - Science WITH Mr. dvorin · What are clouds? •Clouds are formed of tiny droplets of water...

Clouds

Water is strange stuff!

• Gas - water vapour (invisible)

• Liquid - water droplets (visible)

• Solid - ice crystals, hail, snow

Water can occur in 3 states:

What are clouds?

• Clouds are formed of tiny droplets of water or ice.

• Clouds form when water vapour cools and condenses.

• The temperature at which condensation occurs is called dew point.

• Condensation also requires nucleii (small particles) such as dust.

What happens when air is cooled?

• Relative humidity increases.• Dew point is reached (100% relative

humidity).• Water vapour (invisible) condenses to

form water droplets (visible).• Sometimes the water vapor may

change straight into solid state: called Deposition.

• Localized convective lifting occurs where unequal surface heating causes pockets of air to rise because of their buoyancy.

◆Localized Convective Lifting

◆ Convergence• Convergence is when air flows together and rises.

Processes that lift air

Cloud Formation

Orographic Lifting

• Orographic lifting occurs when mountains act as barriers to the flow of air, forcing the air to ascend. The air cools adiabatically; clouds and precipitation may result.

Cloud Formation

• When air is allowed to expand, it cools, and when it is compressed, it warms.

◆ Adiabatic Temperature Changes

• Dry adiabatic rate is the rate of cooling or heating that applies only to unsaturated air.

◆ Expansion and Cooling

• Wet adiabatic rate is the rate of adiabatic temperature change in saturated air.

Air Compression and Expansion

Cloud Formation by Adiabatic Cooling

Cloud Formation

• A front is the boundary between two adjoining air masses having contrasting characteristics.

◆ Frontal Wedging

Processes That Lift Air

Cloud Types and Precipitation

◆ Clouds are classified on the basis of their form and height.• Cirrus (cirrus = curl of hair) are clouds that are

high, white, and thin.• Cumulus (cumulus = a pile) are clouds that

consist of rounded individual cloud masses.• Stratus (stratus = a layer) are clouds best

described as sheets or layers that cover much or all of the sky.

Types of Clouds

Clouds can be classified by their shape and height

Flat clouds eg Stratus (St)

Fluffy cloudseg Cumulus (Cu)

Wispy cloudseg Cirrus (Ci)

Cloud shapes

Clouds can also be classified by height of cloudbase

Low level (below 2000m) eg stratus

Middle level - alto (2,000 to 6, 000m) eg alto-cumulus

High level - cirro (above 6,000m) eg cirrus

Cloud heights

Cloud Classification

Spot the cloud!

Low and flat …..

Stratus

Spot the cloud!Middle level, fluffy …..

Alto -Cumulus

Spot the cloud!

High level, wispy …..

Cirrus

Spot the cloud!Rain bearing, storm clouds …..

Cumulonimbus

World cloud patterns

Can you explain the major world cloud belts?