Weather Part 1: Heating the Earth
Weather is… • the daily condition of the Earth’s atmosphere. • caused by the interaction of heat energy, air pressure, wind, and moisture. • studied by meteorologists.
How Does Heat Energy Move? • Conduction: the movement of heat by direct contact • Convection: the movement of heat by the flow of a fluid (liquid or gas) • Radiation: the transfer of energy as electromagnetic waves. View the Eureka videos: • Conduction • Convection • Radiation
Conduction and the Atmosphere • As the sun shines on the ground it warms up. • Since air is in direct contact with the ground, heat is transferred to the air by conduction.
Convection and the Atmosphere • As air is heated it becomes less dense and rises in the atmosphere. • It is replaced by cooler, more dense air that sinks. • As the warm air rises and cool air sinks it creates convection currents. Which diagram shows what generally happens in the daytime? Nighttime?
Heat Energy and the Atmosphere Radiant energy from the sun can be: • Absorbed by particles in the atmosphere (ozone in the stratosphere; clouds and other particles in the troposphere) • Reflected back into space by clouds or dust in the atmosphere or by the ground • Absorbed by the ground • Radiant energy that is absorbed by the ground is converted into heat energy. • It may then be re-radiated back toward space as infrared radiation into the atmosphere.
The Greenhouse Effect • Some of the infrared rays escape into space. • Some of them are scattered by what are known as greenhouse gases. • When light rays are scattered it means they are absorbed by molecules and then re-emitted in all directions. • Much of the scattered infrared light therefore remains in the Earth’s atmosphere and helps to keep the Earth warm. • Without the greenhouse effect the Earth would be too cold for life as we know it.
The three most important greenhouse gases are carbon dioxide, methane and water vapor.
Temperature Variations • Notice in the diagram that the length of the red line gets longer as you move away from the “equator” even though the amount of “sunlight” is the same for each red line. On the Earth, the red lines would represent the amount of area that receives a given amount of sunlight. • What times of year does this diagram represent?
Temperature Variations • Because of the tilt, the angle of the sunlight, as well as the hours of daylight, change throughout the year for most places on Earth. • This is the primary cause of temperature variations on Earth. • The most radiant energy is receive by the area where the rays are perpendicular (90°)to the Earth’s surface. • As we learned before, the Earth’s axis is tilted 23.5°.
Measuring Temperature • What happens to a substance with it is heated? • Molecules move faster • The substance expands • Air temperature is measured using thermometers. • A liquid-filled thermometer measures temperature change by measuring the amount of thermal expansion that has occurred.
Measuring Temperature • It is now common to measure temperature with electronics. The most common sensor is a thermoresistor (or thermistor). • This device changes its resistance with changes in temperature. • A computer or other circuit measures the resistance and converts it to a temperature
Temperature Scales Celsius, Fahrenheit, and Kelvin • Freezing point of water: 0°C, 32°F, and 273K • Boiling point of water: 100°C, 212°F and 373K • Body temperature: 37°C, 98.6°F and 312K • Room temperature: 20°C, 68°F, and 293K • °C X 9/5 + 32 = °F • (°F – 32) X 5/9 = °C