Warm Up 3/4/08 True or False: The seasons are caused by changes in Earth’s distance from the sun. False Does land or water heat more rapidly? Land heats more rapidly If you move from sea level to a location in the mountains, how will the temperature change? It will get colder

Atmosphere Characteristics Chapter 17, Section 1

Weather No other planet in our solar system has an atmosphere with the exact mixture of gases or the moisture conditions and heat needed to sustain life as we know it Weather is constantly changing, and it refers to the state of the atmosphere at any given time and place Climate is based on observations of weather that have been collected over many years Climate helps describe a place or region The most important measurable properties of weather and climate are air temperature, humidity, type and amount of precipitation, air pressure, and the speed and direction of wind

Weather

Concept Check How does weather differ from climate? Weather changes constantly, but climate is based on patterns of weather that have been observed over years. Climate helps describe a place or region.

Composition of the Atmosphere – Major Components The composition of the atmosphere has changed dramatically over Earth’s nearly 4.6 billion year history The atmosphere is thought to have started from gases that were emitted during volcanic eruptions Air is a mixture of different gases and particles, each with its own physical properties Two gases—nitrogen and oxygen—make up 99% of the volume of clean, dry air

Gases Composing Clean, Dry Air

Composition of the Atmosphere – Variable Components Important materials that vary in the air from time to time and place to place include water vapor, dust particles, and ozone Water vapor is the source of all clouds and precipitation. Movements of the atmosphere allow a large quantity of solid and liquid particles to be suspended within it Ozone – a form of oxygen which combines three oxygen atoms into each molecule (O3) We breath oxygen which has two atoms per molecule (O2) Ozone is concentrated 10 to 50 kilometers above Earth’s surface If ozone did not filter most UV radiation and all of the sun’s UV rays reached the surface of Earth, our planet would be uninhabitable for many living organisms

Composition of the Atmosphere – Human Influence Air pollutants are airborne particles and gases that occur in concentrations large enough to endanger the health of organisms Primary pollutants, are emitted from identifiable sources Secondary pollutants are not emitted directly into the air, they form in the air when reactions take place among primary pollutants and other substances Reactions triggered by strong sunlight are called photochemical reactions

Primary Pollutants

Concept Check What are secondary pollutants? Secondary pollutants are pollutants that form when reactions take place among primary pollutants and other substances.

Height and Structure of the Atmosphere The atmosphere thins as you travel away from Earth until there are too few gas molecules to detect Atmospheric Pressure – weight of the air above (~1000 millibars at sea level) The higher you go in the atmosphere, the less air pressure there will be The atmosphere can be divided vertically into four layers based on temperature (troposphere, stratosphere, mesosphere, and thermosphere)

Atmospheric Pressure Variation with Altitude

Layers of the Atmosphere Troposphere – bottom layer of atmosphere, temperature decreases with an increase in altitude (~0-12 kilometers) This layer essentially has all the weather phenomenon Stratosphere – temperatures gradually increase due to concentration of ozone (~12-50 km) Mesosphere – temperatures again decrease with altitude, going as low as -90ºC (~50-80 km) Thermosphere – no well defined boundary, temperatures increase, due to short-wave solar radiation being absorbed

Thermal Structure of the Atmosphere

Earth-Sun Relationships Solar energy is not evenly distributed over Earth’s surface, but varies with latitude, time of day, and season of the year It is this unequal distribution of heat which creates winds and drives the ocean’s currents Seasonal changes occur because Earth’s axial position relative to the sun continually changes as it travels along its orbit If the axis were not tilted, we would not have seasonal changes

Summer and Winter Solstice occur when Earth’s tilt is pointed away from the sun The Autumnal and Spring Equinoxes occur when the sun’s vertical rays strike the equator (Earth not tilted towards or away from the sun) The length of daylight compared to darkness also is determined by Earth’s position in orbit

Sun Rays Striking Earth

Earth-Sun Relationships

Solstices and Equinoxes

Concept Check In which direction does Earth’s axis point? Earth’s axis points toward the North Star.

Assignment Read Chapter 17 (pg. 476-493) Do Chapter 17 Assessment #1-30 (pg. 499-500) Print out “Investigation 17A – Determining How Temperature Changes with Altitude”

Cool Down Why do seasonal changes occur? Seasonal changes occur because Earth’s axis is tilted. Earth’s orientation to the sun continuously changes as it travels along its orbit. Explain what would happen to air temperatures in the troposphere if carbon dioxide were removed from air. Because carbon dioxide absorbs heat from Earth efficiently, air temperatures would decrease if it were removed from the troposphere. What is one new thing you learned today? Explain.