Page 83 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 2 solar energy to earth and the seasons 47
▲Figure 2.3 Astronaut and solar wind experiment.
Without a protective atmosphere, the lunar surface receives charged solar wind particles and all the sun’s electromagnetic radiation. edwin “Buzz” Aldrin, one of three Apollo XI astronauts in 1969, deploys a sheet of foil in the solar wind experiment. earth­bound scientists ana­ lyzed the foil upon the astronauts’ return. Why wouldn’t this experi­ ment work if we set it up on earth’s surface? [nAsA.]
atmosphere. The corona is the Sun’s rim, observable with the naked eye from Earth during a solar eclipse.
As the charged particles of the solar wind approach Earth, they first interact with Earth’s magnetic field. This magnetosphere, which surrounds Earth and extends be- yond Earth’s atmosphere, is generated by dynamo-like motions within our planet. The magnetosphere deflects the solar wind toward both of Earth’s poles so that only a small portion of it enters the upper atmosphere.
Because the solar wind does not reach Earth’s sur- face, research on this phenomenon must be conducted in space. In 1969, the Apollo XI astronauts exposed a piece of foil on the lunar surface as a solar wind experiment (Figure 2.3). When examined back on Earth, the exposed foil exhibited particle impacts that confirmed the charac- ter of the solar wind.
In addition, massive outbursts of charged material, referred to as coronal mass ejections (CMEs), contrib- ute to the flow of solar wind material from the Sun into space. CMEs that are aimed toward Earth often cause spectacular auroras in the upper atmosphere near the poles. These lighting effects, known as the aurora bo- realis (northern lights) and aurora australis (southern lights), occur 80–500 km above Earth’s surface through the interaction of the solar wind with the upper layers of Earth’s atmosphere. They appear as folded sheets of green, yellow, blue, and red light that undulate across the skies of high latitudes poleward of 65° (Figure 2.4; see www.swpc.noaa.gov/Aurora/ for tips on viewing auroras). In
2012, auroras were visible as far south as Colorado and Arkansas; these sightings may occur farther south with the 2014 solar maximum.
The solar wind disrupts certain radio broadcasts and some satellite transmissions and can cause overloads on Earth-based electrical systems. Astronauts working on the International Space Station in 2003 had to take shel- ter in the shielded Service Module during a particularly strong outburst. Research continues into possible links between solar activity and weather, with no conclusive results. Using satellites to harness the solar wind for power generation is another area of research; major chal- lenges remain.
Electromagnetic Spectrum
of Radiant Energy
The essential solar input to life is electromagnetic energy of various wavelengths, traveling at the speed of light to Earth. Solar radiation occupies a portion of the electro- magnetic spectrum, which is the spectrum of all possible
(a) Aurora australis as seen from orbit.
(b) Aurora borealis over Whitehorse, Yukon, caused by solar activity. On August 31, 2012, a coronal mass ejection erupted from the Sun into space, traveling at over 1450 km·s–1. The CME glanced off Earth’s magnetosphere, causing this aurora four days later.
▲Figure 2.4 Auroras from orbital and ground perspectives.
[(a) Image spacecraft gsFC/nAsA; (b) David Cartier, sr., courtesy of gsFC/nAsA.]