Ch3: Energy Balance and Temperature

1.About the first in-class assignment 2.About reading the textbook

Review of Ch2 – Know 3 methods of energy transfer – Know the names of the 6 wavelength categories in the electromagnetic radiation spectrum – Know the wavelength range of Sun (shortwave) and Earth (longwave) radition – Know the two basic motions of the Earth – Know what causes the seasons: the Earth’s tilt and the 3 ways it affects the solar insolation

Satellite Measurements of the Earth’s Radiation Budget NASA’s Earth Radiation Budget Satellite (ERBS)

Earth’s energy budget (averaged over the whole globe and over a long time At the top of the atmosphere: At the top of the atmosphere: Incoming shortwave = Reflected Shortwave + Emitted longwave Incoming shortwave = Reflected Shortwave + Emitted longwave At the surface: At the surface: Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming) Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming) + Latent heat flux + sensible heat flux + Latent heat flux + sensible heat flux Sensible heat 7% Latent heat 23% Net Longwave 21% Yellow: shortwave Red: longwave

Atmospheric influences on radiation Absorption (absorber warms) ReflectionScattering

Atmospheric Absorption - The Greenhouse Effect Transparent to solar (shortwave) radiation Opaque to earth’s (longwave) radiation Major GH gases: CO 2, H 2 0 (v), CH 4

The wildcard: Clouds! They (1) absorb just about all longwave, and (2) reflect shortwave back to space

The unanswered questions (challenges) in earth’s radiation budget How will the water vapor (H 2 O) change associated with global warming? (Water vapor feedback problem) How will the water vapor (H 2 O) change associated with global warming? (Water vapor feedback problem) How will the clouds change associated with global warming? (Cloud-radiation feedback problem) How will the clouds change associated with global warming? (Cloud-radiation feedback problem) How much do the clouds absorb shortwave radiation? (“Anomalous absorption” problem) How much do the clouds absorb shortwave radiation? (“Anomalous absorption” problem)

3 Types of Scattering: 1.Raleigh 2.Mie 3.Non-Selective Atmospheric Scattering A discussion of each type follows…

1)Rayleigh scattering involves gases, smaller than insolation wavelength scatters light in all directions most effective at short wavelengths (violet, blue)…hence, blue sky explains reddish-orange sunsets when light travels through thick slice of atmosphere

2) Mie scattering –involves aerosols, larger than gas molecules –forward scatter –equally effective across visible spectrum –explains hazy, gray days

3) Non-selective scattering –water droplets in clouds (larger than gas molecules) –Act like lenses; scatter all wavelengths equally –Explains rainbows when viewing rain in the distance (each wavelength bent a wavelength bent a different amount) different amount)

Surface “Sensible” and “Latent” heat transfers 1. Conduction –This is how excess heat in ground is transferred to the atmosphere via an extremely thin layer of air in contact with the surface 2. Convection –Once the heat is transferred from the surface to the air via conduction, convection takes over from here via “sensible” and “latent” heat transfers First, recall 2 other methods of energy transfer in addition to radiation:

Sensible Heat Heat energy which is readily detected Heat energy which is readily detected Magnitude is related to an object’s specific heat Magnitude is related to an object’s specific heat –The amount of energy needed to change the temperature of an object a particular amount in J/kg/K Related to mass Related to mass –Higher mass requires more energy for heating Sensible heat transfer occurs from warmer to cooler areas (i.e., from ground upward) Sensible heat transfer occurs from warmer to cooler areas (i.e., from ground upward)

Latent Heat Energy required to induce changes of state in a substance Energy required to induce changes of state in a substance In atmospheric processes, invariably involves water In atmospheric processes, invariably involves water When water is present, latent heat of evaporation redirects some energy which would be used for sensible heat When water is present, latent heat of evaporation redirects some energy which would be used for sensible heat –Wet environments are cooler relative to their insolation amounts Latent heat of evaporation is stored in water vapor Latent heat of evaporation is stored in water vapor –Released as latent heat of condensation when that change of state is induced Latent heat transfer occurs from regions of wetter-to-drier Latent heat transfer occurs from regions of wetter-to-drier

The unanswered questions (challenges) in earth’s surface fluxes How large are the latent heat flux (evaportranspiration) and sensible heat flux over land? How will they change with global warming? (Land-atmospher feedback problem) How large are the latent heat flux (evaportranspiration) and sensible heat flux over land? How will they change with global warming? (Land-atmospher feedback problem)

Net Radiation and Temperature Earth’s radiation balance is a function of an incoming and outgoing radiation equilibrium (SW + LW = Net) Earth’s radiation balance is a function of an incoming and outgoing radiation equilibrium (SW + LW = Net) If parameters were changed, a new equilibrium would be achieved If parameters were changed, a new equilibrium would be achieved Balances occur on an annual global scale and diurnally over local spatial scales Balances occur on an annual global scale and diurnally over local spatial scales

Daily/Seasonal Radiation Patterns insolation peak vs. temperature insolation peak vs. temperature daily lag daily lag seasonal lag seasonal lag Lag is function of type of surface, wetness, wind, etcLag is function of type of surface, wetness, wind, etc Temperature increases when Temperature increases when input > output input > output Temperature decreases when Temperature decreases when input < output input < output

tropic-to-tropic – energy surplus poles – energy deficits ~ 38 o N/S – balance imbalance of net radiation at surface  Equator/Tropics vs. high latitudes drives global circulation agents: wind, ocean currents, weather systems Latitudinal Variations in Net Radiation

Seasonal variation of surface radiation

Seasonal variation of surface energy budget Storage change = net radiation - latent heat flux - sensible heat flux

Principal Controls on Temperature Principal Controls on Temperature 1. Latitude 2. Altitude 3. Atmospheric Circulation 4. Land-Water Contrasts 5. Ocean Currents 6. Local Effects

Seasonal variation of surface air temperature

T decreases poleward larger T gradient in winter isotherms shift seasonally T over land > water in summer NH steeper T gradient Seasonal Temp Distributions

Temperature Ranges (Summer minus Winter) Large over land, small over ocean

Concepts Earth’s energy balance at the top of the atmosphere and at the surface. What percentage of solar energy is absorbed by the surface? Earth’s energy balance at the top of the atmosphere and at the surface. What percentage of solar energy is absorbed by the surface? Atmospheric influences on radiation (3 ways) Atmospheric influences on radiation (3 ways) What cause the greenhouse effect? What are the major greenhouse gases? What is the “wildcard”? What cause the greenhouse effect? What are the major greenhouse gases? What is the “wildcard”? The three types of atmospheric scattering. What causes the blue sky? Why causes the reddish-orange sunsets? What causes the colors of rainbow? The three types of atmospheric scattering. What causes the blue sky? Why causes the reddish-orange sunsets? What causes the colors of rainbow? Basic characteristics of global temperature distribution (T decreases poleward, isotherm shifts seasonally, T over land > over ocean in summer). Basic characteristics of global temperature distribution (T decreases poleward, isotherm shifts seasonally, T over land > over ocean in summer).

For Wednesday’s lecture Catch up on reading if you haven’t (through Ch4) Catch up on reading if you haven’t (through Ch4)