Chapter 4 Atmosphere and Surface Energy Balances Pearson Education, Inc.

Transcription

1 Chapter 4 Atmosphere and Surface Energy Balances

2 Learning Objectives Identify alternative pathways for solar energy on its way through the troposphere to Earth s surface transmission, scattering, refraction, and absorption. Review the concept of albedo (reflectivity). Explain the greenhouse concept as it applies to Earth. Analyze the effect of clouds and aerosols on atmospheric heating and cooling. Explain four types of heat transfer: radiation, conduction, convection, and advection. Review the Earth atmosphere energy balance and the patterns of global net radiation. Introduce and understand three energy fluxes: sensible heat flux, latent heat flux, and ground heat flux. Plot typical daily radiation and temperature curves for Earth s surface including the daily temperature lag. Explain urban heat island conditions.

3 Energy Pathways

4 Solar radiation transfer in the atmosphere Solar radiation Reflection Atmosphere Reflection is a portion of arriving radiation that bounces directly back into space without being absorbed or performing any work.

5 Solar radiation transfer in the atmosphere Solar radiation Reflection Atmosphere Transmission refers to the passage of shortwave and longwave energy through the atmosphere or water. Transmission

6 Solar radiation transfer in the atmosphere Solar radiation Reflection Absorption Atmosphere Absorption is the assimilation of radiation by molecules of matter and its conversion from one form of energy to another. Transmission

7 Transmission and Absorption Transmission refers to the passage of shortwave and longwave energy through the atmosphere or water. Absorption is the assimilation of radiation by molecules of matter and its conversion from one form of energy to another. CO 2 and water vapor absorb solar radiation and longwave radiation.

8 Transmission and Absorption of Radiation in the Atmosphere Absorption by CO 2, water vapor, and other gases

9 Annual Mean Insolation at Earth s Surface

10 Reflection Reflection is a portion of arriving radiation that bounces directly back into space without being absorbed or performing any work. Albedo is the ratio of reflected solar radiation to the incident solar radiation.

11 Reflection and Albedo

12 Comparison of Albedos Smooth surface versus rough surface Light color surface versus dark color surface Albedo of water surface varies with Sun altitude.

13 July and January Albedos July January

14 Comparison of Albedos Albedo of water surface varies with Sun altitude. As the sunlight s incident angle increases (e.g., from noon to sunset), albedo increases.

15 Water Surface Albedo Incident angle As the sunlight s incident angle increases (e.g., from noon to sunset), albedo increases.

16 Scattering Scattering: changing direction of light s movement, without altering its wavelengths. Rayleigh scattering rule: The shorter the wavelength, the greater the scattering; the longer the wavelength, the less the scattering. The wavelength of blue light is less than red light. Blue sky, red sunrise, and red sunset

17 The Electromagnetic Spectrum Solar radiation consists of: 1. Gamma rays, X-rays, UV (8%) 2. Visible light (47%) 3. Infrared (45%) Shorter 8% 47% 45% 100% solar radiation longer

18 Blue Sky, Red Sunrise and Sunset

19 Refraction Change in speed and direction of light as light passes from one medium to another

20 Refraction Change in speed and direction of light as light passes from one medium to another

21 Mirage

22 The Greenhouse Effect and Atmospheric Warming Atmosphere absorbs heat energy. A real greenhouse traps heat inside. Atmosphere delays transfer of heat from Earth into space.

23 Refraction and Rainbow Primary Rainbow Secondary Rainbow

24 Transmission and Absorption of Radiation in the Atmosphere Absorption by CO 2, water vapor, and other gases

25 Energy Effects of Cloud Types

26 Net Radiation at Earth s Surface Outgoing Shortwave = Albedo Insolation Incoming Shortwave = (1-Albedo) Insolation Net Radiation = Incoming Shortwave Outgoing Longwave

27 Earth Atmosphere Energy System Open system input storage output Energy conservation law Input Output = Storage Change Steady-state equilibrium Input = Insolation Output = Reflected Shortwave + Outgoing Longwave If Input = Output, then Storage Change = 0.

28 Earth s Energy Budget (for the whole Earth) Reflected shortwave Steady-state equilibrium Input = Insolation Output = Reflected Shortwave + Outgoing Longwave If Input = Output, then Storage Change = 0.

29 Steady-state Equilibrium Think Earth as a single system.

30 Spatial Distribution of Average Daily Net Radiation Net Radiation = Incoming Shortwave Radiation Outgoing Longwave Radiation

31 Energy Budget by Latitude Think about the meridional (north-south) transfer agents.

32 Two major meridional energy transfer agents Warm ocean currents Hurricanes

33 Heat Transfer Radiation: energy traveling through air or space Convection: energy transferred by vertical movement Conduction: moleculeto-molecule transfer (from higher temperature to lower temperature) Advection: horizontally dominant movement

34 Convection Advection cold warm cold cold air warm air ground Cold front ground Vertical exchange Horizontal exchange

35 Net Radiation at Surface Net R= SW SW LW LW Net R=(SW +LW )-(SW +LW ) Soil SWê is downward shortwave radiation SWé is upward (reflected) shortwave radiation LWê is downward longwave radiation LWé is upward longwave radiation

36 Sensible Heat Flux (H) Sensible heat flux (H) is the back-and-forth transfer between air and surface in turbulent eddies through convection and conduction. Atmosphere Net R Tair Soil T convection conduction Sensible Heat Flux (H) T is soil temperature, Tair is air temperature If T>Tair, Hé, sensible heat flux from soil to the air If T=Tair, H=0, no sensible heat flux If T<Tair, Hê, sensible heat flux from the air to soil

37 Daily Radiation Patterns

38 Ground Heat Flux (G) Ground heat flux (G) is the energy that flows into or out of the ground surface by conduction. Atmosphere Net R Soil T Ground Heat Flux (G) Td T is surface soil temperature, Td is deep soil temperature If T>Td, Gê, ground heat flux from surface soil to deep soil If T=Td, G=0, ground heat flux is zero If T<Td, Gé, ground heat flux from deep soil to surface soil

39 Latent Heat Flux (LE) Latent heat flux (LE ) is the energy that is stored in water vapor as water evaporates. Atmosphere Net R Soil convection Water Vapor Latent Heat Flux (LE) Evaporation Water absorbs large quantities of this latent heat as it changes state to water vapor, thus removing this heat energy from the surface.

40 Three Phases of Water

41 Surface Energy Balance Net R-(H+LE+G)=Heat Storage Change Atmosphere Net R H Soil G LE

42 Dry Soil versus Wet Soil Net R-(H+LE+G)=Heat Storage Change Atmosphere Atmosphere Net R H LE Net R H LE Dry Soil G Wet Soil G

43 Global Net Radiation

44 Global Latent Heat

45 Global Sensible Heat

46 Energy Budgets at Two Sites El Mirage, CA Pitt Meadows, BC

47 Urban Heat Island

48 Urban Heat Island Dark color = lower temperature Red color = higher temperature

49 Summary of Chapter 4 Solar energy through the troposphere to Earth s surface undergoes transmission, scattering, diffusion, and reflection. Albedo is the reflective quality of a surface. Blue sky, red sunrise, and red sunset are due to scattering. Conduction is the molecule-to-molecule transfer of energy. Convection is the energy transfer by vertical movement. Advection is the energy transfer by horizontal movement. Net radiation is the balance of all radiation at Earth s surface. Net radiation is expended from a non-vegetated surface through three pathways: sensible heat flux, which is the heat energy transfer between air and surface; latent heat of evaporation, which is the energy stored in water vapor as water evaporates; and ground heat flux, which is the energy flows into or out of the ground surface by conduction.