Auroras - Northern and Southern Lights - Essay Example

Auroas: A Critical Review Auroras (otherwise known as northern and southern lights) are often visible from the surface of the Earth at high northern or southern latitudes, and typically appear as luminous bands or streamers that can even extend to altitudes of 200 miles. Auroras are displays of diffuse changing colored light which is seen high in the earth's atmosphere, often taking the form of streamers or drapery and usually green or red. Aurorae occur predominantly in polar regions when energetic charged particles from the sun become trapped in the earth's magnetic field. The rapidly moving particles interact with atoms and molecules in the upper atmosphere and cause them to emit light. In the northern hemisphere they are referred to as the northern lights or aurora borealis, and in the southern hemisphere they are referred to as the southern lights or aurora australis. The subject of these auroras and related issues such as the aurora borealis and aurora australis are of great significance and importance, and in order to come to a clearer and more knowledgeable understanding of these issues, the related information must be addressed thoroughly. The aim of this paper is to discuss all of this, as well as explain how each of the sub-subject matters are related and correlated. This is what will be dissertated in the following. Auroras are caused by high energy particles from the solar wind that are trapped in the Earth's magnetic field. These particles, as they spiral back and forth along the magnetic field lines, come down into the atmosphere near the north and south magnetic poles where the magnetic field lines disappear into the body of the Earth. "The delicate colors are caused by energetic electrons colliding with oxygen and nitrogen molecules in the atmosphere. This excites the molecules, and when they decay from the excited states they emit the light that we see in the aurora." (Csep, n.d.). More intricately, the sun sends a constant stream of charged particles, known as a solar wind, into space; then these energized particles interact with a protective magnet shield that shrouds the planet Earth. The Earth's magnetosphere is a sort of shield, which is made up of invisible lines that radiate out into space from the northern and southern poles. The charged particles squeeze the magnetic field into a teardrop shape, and "In the magnetosphere, researchers say, the interaction creates electric fields and electromagnetic waves that transfer their energy to electrons, which then plunge into the atmosphere." (Britt, 2000). "The aurora varies in intensity from brightness equal to that of the Milky Way up to the equivalent of a full Moon," says climatologist Jan Curtis, who photographs auroras from his home in Alaska. "Colors range from mostly greens to reds, and take on the forms of discrete rays, homogenous brands and arcs, or diffuse glowing clouds. Their movement can be stationary, or zip across the entire sky in seconds." (Britt, 2000). Primary auroral particles have energies between few tens eV and few hundred keV, being higher on the nightside than on dayside. Some of them are even accelerated in the field-aligned direction, which indicates the presence of a special auroral acceleration region. "It can be shown that for 2 keV (100keV) electrons the maximum ionization rate occurs at the altitude of about 130 km (85 km)." (Space, 1998). Whereas the average ionization potential of atoms and molecules is about 15 eV, some experimental data show that fast electrons and protons produce one ion-electron pair per 36 eV, and some excess energy is also left for the product electron; this is what leads to electron heating when the energy is being distributed through and among the ambient electron gas. Auroras are considered to appear as "a glow observed in the night sky, usually the polar zone." (Wikipedia, 2006). It is for this reason that some scientists call auroras 'polar auroras' or 'aurora polaris'. In more northern of latitudes, this occurrence is known as 'aurora borealis', which is Latin for 'northern dawn' since in Europe especially, it often appears as a reddish glow on the northern horizon as if the sun were rising from an unusual direction. Auroras are a common occurrence in the 'ring-shaped zone', and are occasionally seen in temperate latitudes, when a strong magnetic storm temporarily expands the auroral oval. As well, geomagnetic storms that ignite auroras actually happen more often during the months around the equinoxes - early autumn and spring. As Dennis Gallagher, a space physicist at the NASA Marshall Space Flight Center says: "We've known about this seasonal effect for more than 100 years. Some aspects of it are understood, but not all." "At such times the two fields (Earth's and the IMF) link up," says Christopher Russell, a Professor of Geophysics and Space Physics at UCLA. "You can then follow a magnetic field line from Earth directly into the solar wind." (Wikipedia, 2006). James Spann, a space plasma physicist at NASA's Marshall Space Flight Center, explains a recent finding based on satellite data: When a pressure wave of solar radiation hits the leading edge of Earth's magnetosphere, known as the bow, it can cause the shield to contract, and the aurora brightens. As the pressure wave travels along the magnetosphere, the brighter area moves with it, said Spann and his colleagues in a study published in June of 1999. Those who have experienced or witnessed auroras, say that they always remember the "beautiful curtains of ghostly white or colored light shimmering across the sky." (Seekers, n.d.). According to Syun-Ichi Akasofu, director of both the Geophysical Institute and the International Arctic Research Center at the University of Alaska Fairbanks, the aurora may someday help find an answer as to whether or not life exists on other planets. Akasofu has studied the aurora since 1957, and he thinks that other planets' auroras could be used to detect life elsewhere in the universe. The actual idea of this was in fact inspired by the discovery of three planets circling a sun that is much like our own here on the planet Earth, although only a big larger in size. "The star, Upsilon Andromedea, is 44 light years away, which means a spacecraft moving at the speed of light would take 44 years to get there." (Seekers, n.d.). Auroras can appear in many forms - pillars, streaks, wisps, and haloes of vibrating colors - however they are considered as most memorable when they take the form of pale curtains which seem to "float on a breeze of light." (Antarctic, n.d.). It is most commonly that auroral glows form a band which is aligned in a magnetic east-west direction, and if sufficient numbers of energetic electrons are impacting the upper atmosphere, bands may even have shimmering rays extending upwards from them. Active phases of auroral displays last usually on the order of 15 to 40 minutes and may recur in 2 to 3 hours. The auroral displays may appear in many colors with pale green and pink being the most common colors. Different shades of red, yellow, green, blue, and violent have all been observed as well however. "The brightest auroral color is generally a green light emitted by excited oxygen atoms. A red diffuse glow results from another oxygen atom transition. A purple color results from a transition in a Nitrogen molecular ion. The mixture of the major green, red and purple emissions may combine to give aurora a general 'whitish' appearance." (Antarctic, n.d.). The aurora borealis (northern lights) term derives from Latin, and aptly describes the phenomenon that is the aurora borealis. Long ago, the appearance of the aurora borealis caused a range of emotions in the people who witnessed them; they did not know what the occurrence was, and therefore were not sure what to think. People did not understand what it was that was causing these amazing spectacles of light in the sky. The appearance of the aurora borealis can be forecast by following events on the sun in relation to the speed of the gaseous matter which is being thrown off its surface. The northern lights are constantly in motion because of the changing interaction between the solar wind and the Earth's magnetic field. The solar wind most commonly generates up to one million megawatts of electricity in an auroral display and this can cause interference with such things as power lines, radio and television broadcasts and satellite communications. "By studying the auroras, scientists can learn more about the solar wind, how it affects the earth's atmosphere and how the energy of the auroras might be exploited for useful purposes." (Virutal, 2001). The aurora australis (southern lights) is basically the opposite of the aurora borealis (northern lights) and consists of auroras which occur in the southern regions of the world (also called southern lights). The aurora australis is considered as being "mesmerizing, dynamic displays of light that appear in the Antarctic skies in winter. They are, in effect, nature's light show; visual poetry penned from the quantum leaps of atmospheric gases." (Antarctic, n.d.). The literal definition of aurora australis is as follows: aurora is the collective name which is given to the photons (light) that is emitted by atoms, molecules and ions that have been excited by energetic charged particles (principally electrons) which are traveling along the magnetic field lines into the Earth's upper atmosphere (same as aurora borealis). In northern regions such as Alaska, the best time to view aurora is around the time of the equinox (March and late September-October) because this time of the year offers the best trade-off between mild weather and dark skies. During the summer, night skies are not dark enough to view aurora, and in midwinter temperatures the coldness can make aurora viewing unpleasant. In locations which are farther from the average auroral oval, the main consideration involved in this situation is the level of geomagnetic activity, which varies rather unpredictably throughout the year, and therefore is incredibly difficult to forecast. The best time of day to see auroras depends on the location which one is in; in the most active region of the auroral oval, typically the easiest time of visibility in regards to the aurora would be around local midnight. "Spectacular auroral displays due to geomagnetic disturbances may be seen at any time when the sky is dark, but they are relatively unpredictable. Under average conditions, observations around local midnight are most likely to yield results." (Alaska, n.d.). Attempts to record sound during auroras has been attempted numerous times, however so far these attempts have failed to produce any proof that such sounds exist, but it is still hard to ignore the fact that there were numerous reports of sounds during auroras that go back centuries. There are generally two types of sounds that have been reported as accompanying the aurora. "The first is a swishing sound that changes with movements in that auroral display. The second type is a crackling sound, like static electricity makes." (Alaska, n.d.). From this review, we can see that auroras are not only visibly appealing and beautiful, but are also useful in the studying of scientific and other resources. From aurora borealis (northern lights) to aurora australis (southern lights), auroras come in many different shapes, sizes, and forms, but are surely never to be forgotten by those who experience this mesmerizing sight. Auroras have always fascinated and puzzled those who saw them, but a real scientific understanding of how particles flowing from the sun are caught up in the Earth's magnetic field to interact with molecules of atmospheric gases to cause glowing colors is fairly recent. We can also see from this review that you are more likely to observe an aurora if you are at high latitude (extremely southern or northern); however, the Earth's magnetic poles are not exactly in line with the geographic poles, so the latitude of interest would really in fact be the magnetic latitude. Once you know your magnetic latitude (which differs all across the world), as well as how high the Kp index needs to be in order for you to see the aurora at your specific magnetic latitude, it then comes down to choosing a proper viewing time of high magnetic activity by frequently checking the Kp index and SEC forecast. All auroras are spectacular and mesmerizing, and those who have experienced them say that it was one experience they will remember forever. Although even after checking into it and comprehending and deciding on the proper time for one's particular area and time zone viewing auroras can be difficult; it is certainly worth the time and effort. Works Cited Akasofu, Syun-Ichi. "Secrets of the Aurora Borealis." Alaska Geographic Series, 29(1). Alaska. "Aurora." Alaska. 10 May 2006 http://www.pfrr.alaska.edu/aurora/ Antarctic. "Aurora Australis." Antarctic Connection. 9 May 2006 http://www.antarcticconnection.com/antarctic/weather/aurora.shtml Britt, Robert Roy. "What is the Aurora'" Space. 9 May 2006 < http://www.space.com/scienceastronomy/planetearth/aurora_sidebar_2_000202.html> Csep. "Auroras: The Northern and Southern Lights." Csep. 8 May 2006 < http://csep10.phys.utk.edu/astr161/lect/earth/aurora.html> Eather, Robert H. Majestic Lights: The Aurora in Science, History, and the Arts. Washington, D.C.: American Geophysical Union, 1980. Savage, Candace Sherk. Aurora: The Mysterious Northern Lights. San Francisco: Sierra Club Books / Firefly Books, 1994 / 2001. Seekers. "Aurora." Seekers. 8 May 2006 http://seekers.100megs6.com/Aurora's-NightLights.htm> Space. "Aurora." Oulu. 9 May 2006 http://www.oulu.fi/'spaceweb/textbook/auroras.html Virtual. "Aurora." Virtual Finland. 9 May 2006 < http://virtual.finland.fi/finfo/english/aurora_borealis.html> Wikipedia. "Aurora." Wikipedia. 9 May 2006 http://en.wikipedia.org/wiki/Aurora_borealis Read More

 

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