Page 135 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 4 atmosphere and Surface Energy Balances 99
Most shortwave insolation
reflected Sun to space
Cooling effect
Longwave radiation emitted to space
Stratus clouds
(a) Low, thick clouds lead to cloud-albedo forcing and atmospheric cooling.
(c) Contrails over Brittany, France, in 2004. Newer contrails are thin; older contrails have widened and formed thin, high cirrus clouds, with an overall warming effect on Earth.
(b) High, thin clouds lead to cloud-greenhouse forcing and atmospheric warming.
Animation
Global Warming, Climate Change
Animation
Earth–Atmosphere Energy Balance
Most shortwave insolation
transmitted Sun to surface
Cirrus clouds
Warming effect
More longwave radiation absorbed and reradiated
Earth’s surface
◀Figure 4.8 Energy effects of cloud types. [(c) naSa Terra MODiS. (d) naSa Aqua MODiS.]
Earth’s surface
Older contrails
New contrails
weather data from 4000 stations for the three-day shut- down with data from the past 30 years. Their research suggests that contrails reduce the diurnal temperature range (daytime maximum to nighttime minimum) in regions with a high density of aircraft. Active research continues on these ongoing effects of aviation.
Earth–Atmosphere Energy Balance
If Earth’s surface and its atmosphere are considered sepa- rately, neither exhibits a balanced radiation budget in which inputs equal outputs. The average annual energy distribution is positive (an energy surplus, or gain) for Earth’s surface and negative (an energy deficit, or loss) for the atmosphere as it radiates energy to space. However, when considered together, these two equal each other, mak- ing it possible for us to construct an overall energy balance.
The Geosystems in Action feature (pages 100–101) summarizes the Earth–atmosphere radiation bal- ance, bringing together all the elements discussed in
this chapter by following 100% of arriving insolation through the troposphere. Incoming energy is on the left in the illustration; outgoing energy is on the right.
Summary of Inputs and Outputs Follow along the illustration on the next two pages as you read this sec- tion. Out of 100% of the solar energy arriving at the top of the atmosphere, 31% is reflected back to space—this is Earth’s average albedo. This includes scattering (7%), reflection by clouds and aerosols (21%), and reflection by Earth’s surface (3%). Another 21% of arriving solar energy is absorbed by the atmosphere—3% by clouds, 18% by atmospheric gases and dust. Stratospheric ozone absorption accounts for another 3%. About 45% of the incoming insolation transmits through to Earth’s surface as direct and diffuse shortwave radiation. In sum, Earth’s atmosphere and surface absorb 69% of in- comingshortwaveradiation:21%(atmosphereheating) + 45% (surface heating) + 3% (ozone absorption) = 69%.
N 50 km
Cirrus cloud Newfoundland
N 50 km
Young contrails
Aged spreading contrails
(d) Contrails off the Canadian east coast in 2012 expand with age under humid conditions, spreading outward until they are difficult to differentiate from natural cirrus clouds.
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