Page 138 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

102 part I The Energy–atmosphere System
Earth eventually emits this 69% as longwave radiation back into space.
Outgoing energy transfers from the surface are both nonradiative (involving physical, or mechanical, mo- tion) and radiative (consisting of radiation). Nonradia- tive transfer processes include convection (4%) and the energy released by latent heat transfer, the energy ab- sorbed and dissipated by water as it evaporates and con- denses (19%). Radiative transfer is by longwave radiation between the surface, the atmosphere, and space (repre- sented on the right in GIA 4.2 as the greenhouse effect and direct loss to space). Stratospheric ozone radiation to space makes up another 3%.
In total, the atmosphere radiates 58% of the absorbed energy back to space, including the 21% absorbed by clouds, gases, and dust; 23% from convective and latent heat transfers; and another 14% from net longwave ra- diation that is reradiated to space. Earth’s surface emits 8% of absorbed radiation directly back to space, and stratospheric ozone radiation adds another 3%. Note that atmospheric energy losses are greater than those from Earth. However, the energy is in balance overall: 61% at- mospheric losses + 8% surface losses = 69%.
(a) Reflected shortwave radiation on March 18, 2011, near vernal equinox. This is Earth’s albedo. Note high values (white) over cloudy and snowy regions, and lowest values (blue) over oceans.
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CrITICAlthinking 4.1
A Kelp Indicator of Surface Energy Dynamics
in antarctica, on Petermann island off the Graham land Coast, a piece of kelp (a seaweed) was dropped by a pass- ing bird. When photographed (Figure CT 4.1.1), the kelp lay about 10 cm deep in the snow, in a hole about the same shape as the kelp. in your opinion, what energy principles or pathways interacted to make this scene?
now, expand your conclusion to the issue of mining coal and other deposits in antarctica. For now, the in- ternational antarctic Treaty blocks mining exploitation. Construct a case for continuing the ban on mining opera- tions based on your energy-budget analysis of the kelp in the snow and information on surface energy budgets in this chapter. Consider the dust and particulate output of mining. What factors can you think of that might favour such mining? •
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(b) Outgoing longwave radiation emitted from Earth on the same date. Note the highest values (yellow) over deserts, and lowest values (white and blue) over the polar regions.
▲Figure 4.9 Shortwave and longwave images, showing Earth’s radiation-budget components. [CERES instrument aboard Aqua, lang- ley Research Center, naSa.]
Latitudinal Energy Imbalances As stated earlier, energy budgets at specific places or times on Earth are not al- ways the same (Figure 4.9). Greater amounts of sunlight are reflected into space by lighter-coloured land surfaces such as deserts or by cloud cover, such as over the tropi- cal regions. Greater amounts of longwave radiation are emitted from Earth to space in subtropical desert regions where little cloud cover is present over surfaces that ab- sorb a lot of heat. Less longwave energy is emitted over the cooler polar regions and over tropical lands covered in thick clouds (in the equatorial Amazon region, in Af- rica, and in Indonesia).
Figure 4.10 summarizes the Earth–atmosphere energy budget by latitude:
• Between the tropics, the angle of incoming insolation is high and daylength is consistent, with little sea- sonal variation, so more energy is gained than lost— energy surpluses dominate.
• In the polar regions, the Sun is low in the sky, surfaces are light (ice and snow) and reflective, and for up to 6 months during the year no insolation is received, so more energy is lost than gained—energy deficits prevail.
▲Figure CT 4.1.1 [Bobbé Christopherson.]