Clouds…and what

they tell us.

13.11

Clouds (p. 530)

• A cloud is a large collection of tiny water droplets. (100 times smaller than the average rain drop – Fig 2)

• Clouds are formed when warm air rises and then cools at higher altitudes.

• The cooling causes the water vapour to condense (collect together) in tiny water droplets.

• As many water droplets collect together, they can make a rain drop.

• When the rain drop is large enough, gravity causes it to fall to the Earth.

3 Ways Clouds are Made:

1. Convective Clouds:- formed when warm air rises to high altitudes where the water vapour then cools and condenses forming tiny water droplets.

2. Frontal Clouds: (Fig. 3)- formed when the leading or front edge of a large air mass meets another air mass of different temperature. The colder air mass pushes the warmer air up where it condenses forming tiny water droplets.

3. Orographic Clouds: (Fig. 4)- When objects, such as mountains, force air to go up. When the air hits the cooler air at higher altitudes, condensation occurs.

Fog

• Fog is actually a cloud that forms near the ground.

• Fog is produced on clear nights when energy from the surface radiates upward but is not reflected back to the Earth by any clouds.

• Thus, the air near the ground cools, allowing water vapour to condense into fog.

Cloud Shapes

The two main cloud shapes are:

Cumulus – a billowing, rounded shape

Stratus – a flattened, layered shape

1) Cumulus CloudsLook like big cotton balls in the sky. Have very large spaces of clear sky between

them. Usually indicate unstable conditions Normally they don't carry any rain, but can

change into cumulonimbus (thunder) clouds.

2) Stratus Clouds

• Tend to grow horizontally

• Indicate stable conditions

3) Cirrus Cloud are:Thin and wispyFound very high in the skyPoint in the direction the wind is blowingNo precipitation falls from cirrus cloudsA sign of fair weather

• Nimbus means low level, rainy cloud

• Alto means mid-level cloud (not real high or low)

• Cirrus means high level cloud

Classification of CloudsBLM 13.11

The Water Cycle

Chapter 13.8

The Hydrosphere

All of the Earth’s water, both fresh and salt, forms what is called the hydrosphere.

• Only a small portion of the hydrosphere is fresh water (2.5%) and of this

• the majority is frozen in glaciers and polar ice caps, and the rest is mainly underground, or surface water (lakes, rivers, etc.)

The Hydrosphere

• 97.5% is salt water

• Canada is one of the luckiest countries in the world b/c our population is just .5% of the world total, yet we have almost 10% of the world’s supply of fresh water.

• B/C so much of the Earth’s surface is water, our weather systems depend greatly on it.

WATER CYCLE (Hydrologic Cycle)

Water on Earth is always changing. Its repeating changes make a cycle. As water goes through its cycle, it can be a solid (ice), a liquid (water), or a gas (water vapour).

How do these changes happen?

WATER CYCLE

Adding or subtracting heat makes the cycle work.

If heat is added to ice, it melts. If heat is added to water, it evaporates.

Evaporation occurs when liquid water turns into a gas called water vapour.

If heat is taken away from water vapour, it condenses.

WATER CYCLE

Condensation occurs when water vapour turns into a liquid.

If heat is taken away from liquid water, it freezes to become ice.

Ice changing directly to vapour (skipping the liquid stage), is called sublimation.

Transpiration occurs when water evaporates from plants.

Terms to know• Evaporation

– the change of state from liquid to gas– This is the purest naturally occurring water

• Condensation– The change of state from water vapor to liquid– Forming cloud stage

• Precipitation– Water that falls to the ground– Example: rain, snow, sleet, hail

• Runoff– The water that flows over the ground surface

• Percolation– The water that soaks into the ground forming pockets of groundwater. The

downward movement of water through soil and rock• Sublimation

– Transition from solid to gas (no liquid phase)• Transpiration

– The loss of water vapor through the leaves of plants into the atmosphere

Hydrologic Cycle = Water Cycle