Chapter Six: Weather and Climate • 6.1 Introduction to Weather • 6.2 Weather Patterns • 6.3 Climates and Biomes
Investigation 6A Observing the Weather • How can you use weather data to make predictions?
6.1 Introduction to Weather • Weatheris 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 Pressure • When warm air rises from Earth’s surface, an area of low pressure is created. • This lower-pressure area draws in air from surrounding higher-pressure areas. • Eventually the warm air that rose from the surface cools and becomes more dense. • Dense, cool air sinks back to the surface causing an area of high pressure. • 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 humidityis a measure of how much water vapor an air mass contains.