Water and Weather

Chapter Six: Weather and Climate

• 6.1 Introduction to Weather

• 6.2 Weather Patterns

• 6.3 Climates and Biomes

Investigation 6A

• How can you use weather data to make predictions?

Observing the Weather

6.1 Introduction to Weather• Weather is a term

that describes the condition of the atmosphere in terms of temperature, wind, and atmospheric pressure.

6.1 Temperature• Heated air near a hot surface

is less dense than the colder air above it.

• The heated air rises, forcing the colder air to move aside and sink toward the ground.

• Then this colder air is warmed by the surface, and it rises.

• Wind is created.

6.1 Pressure1. When warm air rises from Earth’s

surface, an area of low pressure is created.

2. This lower-pressure area draws in air from surrounding higher-pressure areas.

3. Eventually the warm air that rose from the surface cools and becomes more dense.

4. Dense, cool air sinks back to the surface causing an area of high pressure.

5. This new high pressure may become the source of more wind.

6.1 Convection in the atmosphere• Convection near coastlines causes sea

breezes during the day and land breezes at night.

6.1 Convection in the atmosphere• A small upward flow

of warm air is called a thermal.

• Pilots of sailplanes (which lack engines) fly by riding the thermals.

6.1 Convection cells• The combination of

global convection and Earth’s rotation sets up a series of wind patterns called convection cells.

6.1 Coriolis effect• The bending of currents of air due to the

Earth’s rotation is called the Coriolis effect.

6.1 Air and water vapor

• Three important global wind patterns exist in each hemisphere:

– Trade winds– Prevailing westerlies– Polar easterlies

6.1 Air and water vapor• Water in gas form is

called water vapor.• Like a soggy sponge, air

reaches a point and can’t hold anymore vapor.

• The vapor turns back into liquid and form droplets.

Use these pictures to explain how the cycle can continue.

6.1 Relative Humidity• Relative humidity is a measure of how

much water vapor an air mass contains.