Geomagnetism of earth.


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Geomagnetism of earth.

  2. 2. CONTENTS S.No TITLE PAGE Abstract 1.0 1.1 1.2 2.0 2.1 2.2 2.3 3.0 3.1 3.2 4.0 4.1 4.2 5.0 04 Introduction Background Objective Magnetic Field Earth’s Magnetic Field Main Field Magnetic and Geographic Poles Factors Which Affect Geomagnetism Curie Temperature Dynamo Theory Evidences of Magnetic Field Solar Winds Auroras Conclusion 05 05 05 05 05 06 07 07 07 08 09 09 10 12 LIST OF FIGURES FIGURE Figure: 1 TITLE Earth’s Magnetic Field PAGE 06 2
  3. 3. Figure: 2 Figure: 3 Geomagnetic Reversal Dynamo Effect 08 09 ABSTRACT In our report we have started with a brief introduction covering the background of what magnetic field is? The different factors on which Earth’s magnetic field depends. 3
  4. 4. Then we have researched about the history of geomagnetism. In the research then we covered the different evidences which support geomagnetism, the different studies related to it etc. Further, we investigated rock magnetism, its types, paleomagnetism and its applications. 1. INTRODUCTION 1.1 Background The magnetic field is a complex part of Earth. While an understanding of the basics of magnetism is essential, the temperatures at the core of the Earth where the field originates require scientists to look beyond ferromagnetic properties and bar magnets for the field’s 4
  5. 5. origin. These observations, along with the current conditions of our magnetic field, have lead some scientists to hypothesize that presently Earth is entering a period of magnetic reversal. Which indicates that the study of geomagnetism will be very essential for scientists in the near past as it is today? 1.2 Objective The main objective of our report is to show that how the Earth’s magnetic field affects geomagnetism and how in turn geomagnetism helps us in understanding the history of the Earth, the magnetic reversals which have taken place after intervals (several hundred to thousands of years), etc. In other words we have highlighted the affects of Earth’s magnetic field and how it is related to geomagnetism and related phenomenon’s. 2. MAGNETIC FIELD This magnetic field is just like the one created by a magnet, much like the electric field. Lines originate at the North Pole and terminate at the South Pole. 2.1 Earth’s Magnetic Field (a) Definition Earth's magnetic field (also known as the geomagnetic field) is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun. (b) Explanation Earth’s magnetic field is approximately the field of a magnetic dipole tilted at an angle of 11 degrees with respect to the rotational axis—as if there were a bar magnet placed at that angle at the center of the Earth. However, unlike the field of a bar magnet, Earth's field changes over time because it is really generated by the motion of molten iron alloys in the 5
  6. 6. Earth's outer core (the geodynamo). The Magnetic North Pole wanders, fortunately slowly enough that the compass is useful for navigation. At random intervals (averaging several hundred thousand years) the Earth's field reverses (the north and south geomagnetic poles change places with each other). 2.2 Main Field Although the Earth’s Magnetic Field is often represented as a bar magnet, it is much more complicated than that. The main field includes the field at the surface of the Earth, magnetic poles, and the magnetosphere. Figure: 1 Earth’s Magnetic Field 2.3 Magnetic and geographic poles Earth's geographic poles are fixed by the axis of Earth's rotation. On maps, the north and south geographic poles are located at the congruence of lines of longitude. Earth's geographic poles and magnetic poles are not located in the same place fact they are hundreds of miles apart. As are all points on Earth, the northern magnetic pole is south of the northern geographic 6
  7. 7. pole (located on the polar ice cap) and is presently located near Bathurst Island in northern Canada, approximately 1,000 mi (1,600 km) from the geographic North Pole. The southern magnetic pole is displaced hundreds of miles away from the southern geographic pole on the Antarctic continent for instance. Although fixed by the axis of rotation, the geographic poles undergo slight wobble-like displacements in a circular pattern that shift the poles approximately six meters per year. Located on shifting polar ice, the North Pole (geographic pole) is technically defined as that point 90° Latitude, 0° longitude (although, because all longitude lines converge at the poles, any value of longitude can be substituted to indicate the same geographic point). Latitude growth 1800-2012: from 1 billion to 7 billion estimated in 31.10.2011. 3. FACTORS WHICH AFFECT MAGNETISM 1. Curie temperature 2. Dynamo effect 3.1 Curie temperature (a) Definition The Curie temperature (Tc), or Curie point, is the temperature at which a ferromagnetic or a ferrimagnetic material becomes paramagnetic on heating; the effect is reversible. (b) Explanation Below the Curie temperature neighboring magnetic spins are aligned parallel within ferromagnetic materials and anti-parallel in ferrimagnetic materials. As the temperature is increased towards the Curie point, the alignment (magnetization) within each domain decreases. Above the Curie temperature, the material is paramagnetic so that magnetic moments are in a completely disordered state. As shown in the figure below: 7
  8. 8. Figure: 2 Geomagnetic Reversals 3.2 Dynamo Theory Planets do not have giant bar magnets in their cores, so what produces the magnetic field? Circulating electrical charges can produce a magnetic field. A theory called the magnetic dynamo theory says that swirling motions of liquid conducting material in the planet interiors produce the magnetic field. In geophysics, dynamo theory proposes a mechanism by which a celestial body such as the Earth or a star generates a magnetic field. The theory describes the process through which a rotating, convecting, and electrically conducting fluid can maintain a magnetic field over astronomical time scales. Rotation of the Earth causes a similar, though not simultaneous, rotation in the conducting, liquid metal core which flows across the existing magnetic field. Electric currents are induced, creating a second magnetic field. This second magnetic field reinforces the first and a dynamo is created which sustains itself. There are three requisites for a dynamo to operate: 8
  9. 9. (a) An electrically conductive fluid medium. (b) Kinetic energy provided by planetary rotation. (c) An internal energy source to drive convective motions within the fluid. (d) Figure: 3 Dynamo Effect In the case of the Earth, the magnetic field is induced and constantly maintained by the convection of liquid iron in the outer core. A requirement for the induction of field is a rotating fluid. Rotation in the outer core is supplied by the Coriolis Effect caused by the rotation of the Earth. The Coriolis force tends to organize fluid motions and electric currents into columns (also see Taylor columns) aligned with the rotation axis. 4. EVIDENCES OF MAGNETIC FIELD (a) Magnetosphere (b) Auroras 4.1 Solar wind The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 9
  10. 10. 10 keV. The stream of particles varies in temperature and speed over time. These particles can escape the Sun's gravity because of their high kinetic energy and the high temperature of the corona. As the solar wind approaches a planet that has a well-developed magnetic field (such as Earth, Jupiter and Saturn), the particles are deflected by the Lorentz force. This region, known as the magnetosphere, causes the particles to travel around the planet rather than bombarding the atmosphere or surface. The magnetosphere is roughly shaped like hemisphere on the side facing the Sun, then is drawn out in a long wake on the opposite side. The boundary of this region is called the magnetopause, and some of the particles are able to penetrate the magnetosphere through this region by partial reconnection of the magnetic field lines 4.2 Auroras Aurora(plural: aurora or auroras) is a natural light display in the sky particularly in the high latitude (Arctic and Antarctic) regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere (thermosphere). The charged particles originated in the magnetosphere and solar wind and, on Earth, are directed by the Earth's magnetic field into the atmosphere. Auroras are caused by the interaction of energetic particles (electrons and protons) from outside the atmosphere with atoms of the upper atmosphere. Such interaction occurs in zones surrounding the Earth's magnetic poles. Auroras in the Northern Hemisphere are called aurora borealis, or northern lights; in the Southern Hemisphere they are called aurora Australis, or southern lights. Auroras are caused by the interaction of energetic particles (electrons and protons) from outside the atmosphere with atoms of the upper atmosphere. Such interaction occurs in zones surrounding the Earth's magnetic poles Auroras in the Northern Hemisphere are called aurora borealis, or northern lights; in the Southern Hemisphere they are called aurora Australia, or southern lights. 10
  11. 11. 5. CONCLUSION Currently, the poles are drifting rapidly and the field is steadily weakening. The South Atlantic Anomaly also provides support for reversal. If a reversal was to occur, harmful ionized particles from the Sun would enter Earth’s atmosphere, with varying consequences. 11
  12. 12. However, there is some debate over whether or not a reversal is in progress. The changes in the field are within the expected limit and are simply due to the random flow of the Dynamo. Finally, the Moon will have an adverse affect on Earth’s magnetic field over time. It is clear that geomagnetism is a very dynamic and complex topic that includes much theory and debate about its past, present, and future. 12