11.2 Learning Goals Explain the causes of weather. Discuss the role of convection in moving air through Earth’ s atmosphere. Describe the characteristics of Earth’s major climate regions.
Investigation 11B Key Question How can you use weather data to make predictions? Observing the Weather
11.2 Weather Variables Weather is a term that describes the condition of the atmosphere in terms of temperature, wind, and atmospheric pressure. There are many conditions on earth that affect how and why weather changes.
11.2 Convection, pressure, and wind Convection occurs naturally in Earth’s atmosphere due to the heating and cooling of air. A thermal is a small, upward flow of warm air caused by convection. Gliding birds like hawks often ride a thermal as they hunt.
11.2 Convection 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.
11.2 Wind An air mass is a large body of air with consistent temperature and moisture content throughout. Wind is the horizontal movement of air that occurs as a result of a pressure difference between two air masses.
11.2 Convection in the atmosphere Convection near coastlines causes sea breezes during the day and land breezes at night.
11.2 Global Convection The combination of global convection and Earth’s rotation sets up a series of wind patterns called convection cells.
11.2 Polar fronts At a boundary called the polar front, the dense, polar air forces the warmer, westerly air upward. During the winter, polar fronts slide toward the equator and during the summer they retreat northward.
11.2 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.
11.2 Precipitation Rain is the result of a cooling air mass. Cooling an air mass is like wringing out a wet sponge. Tiny droplets form a cloud or fog. Larger droplets fall as rain.
11.2 Precipitation Tiny water droplets are suspended in the atmosphere. Whether the particles are liquid water or water vapor depends changes in pressure and temperature.
11.2 Precipitation When the rate of evaporation is greater than the rate of condensation, we see clearing skies. When the rate of condensation exceeds the rate of evaporation, it rains.
11.2 Snow Snow usually forms when both ice crystals and water droplets are present in the sky. The water droplets attach to ice crystals and freeze. When the ice crystals are large enough, they will fall to the ground.
11.2 Relative Humidity Relative humidity is a measure of how much water vapor an air mass contains.
11.2 Climate and biomes Climate is the type of weather that a place has, on average, over a long period of time. Climate depends on many factors: latitude, precipitation, elevation, topography, and distance from large bodies of water.
11.2 Climate and biomes Scientists divide the planet into climate regions called biomes. Earth has six main biomes: deserts, grasslands, temperate deciduous forests, rainforests, taiga, and tundras. Each biome has a unique set of plants and animals that thrive in its climate.
11.2 Climate and biomes The Serengeti is a home to thousands of predators species and 1.6 million herbivores.
11.2 Climate and biomes Humidity is related to plant and animal diversity. From the poles to the equator, humidity and the diversity of plants and animal increases.
11.2 Biomes and temperature At the equator, sunlight is direct and intense. As a result, the average yearly temperature at the equator is 27 °C (80 °F), while at the North Pole it is -18 °C (0 °F).
11.2 Biomes and elevation Elevation is another important factor in determining the type of biome.
11.2 Biomes and temperature Compare the data below for Portland, OR and Minneapolis, MN. If these cities are about the same latitude, why don’t they have the same climate?
11.2 Biomes and temperature The differences in temperature between the two cities have to do with water. Water warms up and cools down slowly. Regions near water—like Portland, OR—do not have extremely hot or cold weather, even though they are farther north.
11.2 Plants and animals in biomes A biome consists of plant and animal communities. The plants and animals in a community survive in a shared environment.
11.2 Plants and animals in biomes Within a biome, there are many interrelated ecosystems. An ecosystem is made up of the plants and animals that live there, plus nonliving things like soil, air, water, sunlight, and nutrients.
11.2 Plants and animals in biomes What features of this jackrabbit help it survive in it’s desert biome?