The Earth’s atmosphere is divided into five layers. The first layer, closest to earth’s surface, is the troposphere. This is where all of our weather occurs—clouds, wind, lightning, hurricanes, rain, snow, and tornadoes. Because air density is greatest near the surface and diminishes with height, the troposphere contains about 80% of the atmosphere’s mass. All of the air we breathe is in the troposphere, so it is here that air pollution is of greatest concern. Temperature is typically warmest near the ground and cools with height in the troposphere, which helps drive the weather and the mixing of pollutants.
The next layer is the stratosphere. This is where ultraviolet radiation from the sun reacts with oxygen to form ozone gas and the ozone layer. The oxygen and the ozone layer protect us from the cancer-causing ultraviolet radiation. This absorption of radiation causes temperatures to increase with height in the stratosphere, in contrast to cooling with height in the troposphere. This temperature pattern causes the stratosphere to be very stable; in other words, air rises and sinks very slowly in this layer.
The next layer is the mesosphere, which stops meteors and other fragments of things that come from space. The next layer is the thermosphere, where space shuttles orbit the earth. Finally, the last layer is the exosphere, which is the outermost portion of our atmosphere and is the layer in which satellites orbit the Earth. Outside of this layer lies space.
The two most obvious ways that we experience the atmosphere are through its temperature and its winds. Temperature is a physical property that measures how “hot” or “cold” something is. Microscopically, it is a measure of the average kinetic energy or speed of the molecules that make up the system. Temperature can be measured in Kelvin, Celsius, and Fahrenheit.
The GLOBE instruments will allow students to measure both the surface temperature (the temperature of Earth’s surface or other objects) and the air temperature (the temperature of the air). Air and surface temperature measurements are not always equal at a given location. That’s because surfaces tend to change temperature more quickly than the air, warming more quickly during the day and cooling more quickly at night. Some surfaces warm more quickly than others due to their color and composition, and this can affect the temperature of the air above them. You may want to have students experiment with measuring the temperatures of different surfaces outside.
An urban heat island occurs when a metropolitan area is significantly warmer than surrounding rural areas. This happens because surfaces like asphalt and concrete warm up quickly and conduct their heat to the air; by contrast, much of the energy absorbed by vegetation dissipates by evapotranspiration (the sum of evaporation and plant transpiration from the Earth’s surface to the atmosphere). Waste heat from our use of energy adds to the heat island.
Differences in temperature due to the Sun’s uneven heating of the Earth are the driving force behind wind, or moving air. A classic example of how temperature differences cause the wind to blow is the sea breeze. On summer days near the coast, the land warms faster than the sea. This creates a wind circulation pattern in which near the ground wind blows from sea to land. At night, a “land breeze” may blow in the opposite direction as the land cools more quickly than the sea.
A sea breeze circulation on a summer day
Students will use the wind vane to discover from what direction the wind is blowing. Though students will not directly measure wind speed, they can get a sense of it by feeling the wind blow and checking wind speed in weather reports.
Answer Key to Lesson 2 Student Worksheets
