2: Warming the Earth and the Atmosphere
- Page ID
- 46694
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Introduction
Outside on a sunny day, you can feel the sun’s energy on your skin. You can feel it as heat. Standing under the shade of a tree (which blocks the sun’s rays) makes a significant difference in temperature and in your probability of getting a sunburn. The closest Earth gets to the Sun is approximately 93 million miles. How does the sun’s energy reach so far? What does the Earth do with all this energy? And how does it affect our weather?
By the end of this chapter, you should be able to:
- Define Air temperature and convert between different scales
- Name and describe the three modes of heat transfer
- Define blackbody radiation and apply Wien’s law to determine the maximum emission wavelength
- Describe Earth’s surface radiation budget, including shortwave and longwave components
- Describe the cause of seasons on Earth
- 2.1: Temperature
- This page explains air temperature as the average kinetic energy of air molecules, influencing their motion. It presents three temperature scales: Fahrenheit, Celsius, and Kelvin, along with key conversion formulas. It highlights that Kelvin begins at absolute zero, where molecular motion stops, and underscores the linear relationship between Celsius and Kelvin.
- 2.2: Latent Heat
- Latent heat is the energy involved in phase changes of water, such as melting, evaporation, condensation, and freezing. Heat added to ice at 0°C causes melting without a temperature change, and the importance of these processes in atmospheric science, particularly in weather phenomena such as convection and thunderstorms. Different phase changes have varying latent heat requirements, with vaporization needing more energy than melting.
- 2.3: Heat Transfer
- This page explains kinetic energy in the context of thermal energy, linking it to the movement of molecules and temperature. It covers how temperature reflects average molecular kinetic energy and describes heat transfer methods: conduction (direct contact), convection (in fluids), radiation (without contact), and latent heat. Higher molecular speeds correspond to higher temperatures.
- 2.4: Electromagnetic waves
- We examine radiation as electromagnetic waves generated by electric and magnetic fields, categorized by wavelength into types like radio waves and x-rays. We highlight the inverse relationship between wavelength, frequency, and temperature: colder objects emit lower frequencies and longer wavelengths, while warmer objects emit higher frequencies and shorter wavelengths. This principle is consistent across various temperature scales, from near absolute zero to millions of Kelvins.
- 2.5: Characterizing Emission
- This page covers the sources of electromagnetic energy emitted by objects above absolute zero, explaining blackbody radiation and Planck's curves related to temperature. It highlights Wien's Law for determining maximum wavelength emitted, indicating that hotter objects emit shorter wavelengths.
- 2.6: Radiation Interaction with the Atmosphere
- We focus on the interaction between solar and thermal radiation and Earth's atmosphere, highlighting the crucial role of greenhouse gases, particularly water vapor. It discusses the contributions of other gases like CO2, O2, O3, CH4, and N2O.
- 2.7: Surface Energy Balance
- This page explains the energy balance of the Earth-Sun system, focusing on the significance of incoming solar radiation and outgoing emissions. It details the solar constant of about 1361 W·m-2, the inverse square law regarding radiation intensity, and the net radiation budget equation. Additionally, it discusses albedo and the differences between shortwave and longwave radiation, underscoring the importance of this energy balance for maintaining Earth's temperature stability.
- 2.8: Variations in Radiation
- We explain how solar radiation varies on Earth due to factors such as eccentricity, obliquity, and precession, thereby affecting climate over different time scales. Seasons result from Earth's axial tilt rather than its distance from the Sun. Additionally, it covers daily cycles of solar absorption and infrared emission. The chapter stresses the importance of radiation definitions, the Earth's radiation budget, and the dynamics that alter seasonal and daily temperatures.
- 2.9: Exercises
- Some exercises to review the topics covered in this chapter.
Thumbnail: A Hawaiian sunset by Edmund Garman is licensed under CC BY 2.0.