Earth Magnetic Field by Research From Web by Compiling It (Dissertat. Methodology Sample)

MAGNETIC FIELD OF EARTH
Definition:
"The earth's magnetic field is the magnetic field that surrounds the earth. It is sometimes called a geomagnetic field. The earth's magnetic field is created by rotation of earth and theearth's core".
Explanation:
It shields the earth against harmful particles in space. The magnetic fields extends from the earth's interior to where it meets the solar wind, a stream of charged particles emanating from the sun. Its magnitude at the earth's surface ranges from 25 to 65 microtesla (0.25 to 0.65 gauss).It is approximately the field of a magnetic dipole titled at an angle of 10 degrees with respect to rotational axis as if there were a bar magnet placed at that angle at centre of earth. However unlike the field of a bar magnet, Earth's field changes over time because it is generated by the motion of molten iron alloys in the earth's outer core (the geodynamo).
The north magnetic pole wanders, but does so slowly enough that an ordinary compass remains useful for navigation.However,at random intervals, which average about several hundred thousand years, the earth's field reverses, which causes the north and south magnetic poles to change places with each other. These reversals of geomagnetic poles leave a record in rocks that allow paleomagnetists to calculate past motions to continents and ocean floors as a result of plate tectonics.
The region above the ionosphere is called magnetosphere, and extends several tens of thousands of kilometers into space. This region protects the earth from cosmic rays that would otherwise strip away the upper atmosphere, including ozone layer that protects the earth from harmful ultraviolet radiation.
The solar wind is a stream of ionized gases that blows outward from the sun at about 400km\sec and that varies in intensity with the amount of surface activity on the sun. The earth's magnetic field shields it from much of solar wind. When the solar wind encounters earth's magnetic field it is deflected like water around the bow of a ship.
The imaginary surface at which the solar wind is first deflected is called the bow shock. The corresponding region of space sitting behind the bow shock and surrounding the earth is termed the magnetosphere, it represents a region of space dominated by earth's magnetic field in the sense that it largely prevents the solar wind from entering. However, some high energy charged particles from solar wind leak into magnetosphere and are source of charged particles trapped in the Van Allen Belts.
Earth's magnetic field (and the surface of magnetic field) is approximately a magnetic dipole, with one pole near the north pole and other near the geographic south pole. An imaginary line joining the magnetic poles would be inclined by approximately 11.3i from the planet's axis of rotation. The cause of field is probably explained by the dynamo theory. The magnetic field extends several tens of thousands of kilometers into space as the magnetosphere.
Earth's magnetic field, predominantlydipolar at its surface ,is distorted further out by the solar wind .This is a stream of charged particles leaving the sun's corona and accelerating to a speed of 200 to 1000 kilometersper second. They carry with them a magnetic field ,the interplanetarymagnetic field.
The solar wind exerts a pressure ,and if it could reach earth's atmosphere it would erode it.However,it is kept away by the pressure of earth's magnetic field. Themagnetopause, the area where the pressures balance ,is the boundary of magnetosphere, Despite its name, the magnetosphere is asymmetric, with the sunward side being about 10 earth radii out but the other side stretching out in a magnetotail that extends beyond 200 earth radii,Sunward of the magnetopause is the bow shock,the area where the solar wind blows abruptly.
Inside the magnetosphere is the plasmasphere,a donut shaped region containing low energy charged particles,or plasma.This region begins at height of 60 km,extends upto 3 or 4 earth radii,and includes the ionosphere.This region rotates with Earth.There are also two concentric tire shaped regions,called van ellen radiation belts,with high energy ions (energies from 0.1 to 10 million electron volts).The inner belt is 1-2 earth radii out while the other belt is at 4-7 earth radii.The plasmasphere and van allen belts have partial overlap,with extent of overlap varying greatly with solar activity .
As well as deflecting the solar wind,the earth's magnetic field deflects cosmic rays,high-energy charged particles that are mostly from outside the solar system.
Astronauts on the moon risk exposure to radiation .Anyone who had been on the moon's surface during a particularly violent solar eruption in 2005 would have recieved a lethal dose.Some of the charged particles do get into the magnetosphere.These spiral around field lines,bouncing back and forth between the poles several times per second.In addition ,positive ions slowly drift westward and negative ions drift eastward,giving rise to a ring current,This current reduces the magnetic field at the earth's surface.Particles that penetrate the ionosphere and collide with the atoms ,there give rise to the lights of the aurorae and also emit x-rays.
The varying conditions in the magnetosphere ,known as space weather,are largely driven by solar activity .If the solar wind is weak ,the magnetosphere expands;while if it is strong,it compresses the magnetosphere and more of it gets in periods of particularly intense activity,called geomagnetic storms,can occur when a coronal mass ejection erupts above the sun and sends a shock wave through the solar system.Such a wave can take just two days to reach the earth,Geomagnetic storms can cause a lot of disruption;the "HALLOWEEN" storm of 2003 damaged more than a third of NASA'S satellites.The largest documented storm occured in 1859.It induced currents strong enough to short out telegraph lines,and aurorae were reported as far south as HAWAII.
Importance Of Magnetic Field:
The earth's magnetic field acts as a shield against the harmful particles that come from the solar wind. The absence of a magnetic field in planets such as earth would render them inhabitable,espacially by humans. Calculations of loss of carbon dioxide from atmosphere of Mars, resulting from scavenging of ions by solar wind indicates dissipation of magnetic field ofMars.
Magnetic Poles:
Magnetic declination ,defined as the angle between true north and the horizontal component of the field measured eastward from true north. The location of magnetic poles is not static but wander as much as 15 km every year. (Doctor david p.stern,emritus goddard flight centre, NASA).The pole position is usually not that indicated on many charts and many magnetic pole mocking brings a confusion as to what is being located at the given position.The geomagnetic poles position are usually not close to the position that commercial cartographers place "Magnetic poles".Geometric dipole poles "IGRF Model dip poles"and "Magnetic dip poles" are variously used to denote the magnetic poles. The earth's field is changing in size and position. The two poles alter independently of each other and are not at dirrectly opposite position on the globe. Currently the south magnetic pole is farther from the geographic south pole then the north magnetic pole is form the north geographic pole. Magnetic and geomagnetic poles are two types of magnetic poles. The magnetic poles are the two position on the earth's surface where the inclination of the earth's field is 90 degree at the north magnetic pole and -90 degree at the south magnetic pole. The geomagnetic poles are the two positions where axis of dipole best fits the intersection between the earth's field and the earth's surface. The geomagnetic and magnetic poles would coincide if earth's field was dipolar.Due to many non-dipolar terms,they position in different places.The positions of the magnetic poles are not static and they wander about km every year.The earth's field changes in strength and position and the two poles wander independently but never get positioned opposite each other.The earth's magnetic field is generated by the electric currents flowing in the slowly moving molten iron.Hence ,it can trap charged particles such as electrons and protons and force them to execute a spiraling motion back and forth along the field lines.
HISTORY:
The earth's magnetic field has been linked to navigation for over 1000 years.The compass in different forms was a valueable aid for ancient navigators, and it is not possible to imagine today's orienteering rumors or hikers in fog and bad weather with out it.
In the 15th century it became clear that compass needle did not point exactly towards geographic north pole. Navigators and cartographers learned to cope with this deviation, called declination. However, diclination is not same every where. This variation became clear as early as in the 16th century,when the first measurements of declination were made. The first document measurement of declination in Norway was made in 1596 byWilliam Barantz.
The scientific exploration of the earth magnetic field started with english man William M.Gibert's book,"The magnete", published in 1600.Gilbertb made a magnetic model of earth and showed by means of compass that the direction of magnetic field varied with where on earth was located. He concluded,"Magnus Magnese Ipse Est Globus terrestris",which means,"The earth itself is the big magnet". In addition he suggested the source for magnetic field was to be found inside the earth.
In 18th century it became clear that earth's magnetic field changes over time, with variations in both directions and amplitude over years, decedes and centuries. Short term variations where subsequently detected. Hence christian orsted (1777 - 1851) discovered that electric currents cause magnetic fields. The pioneer in Nor...