Gyrocompass Effect And The Origin Of The Earth's Magnetic Field Low Yuen Wang (Malaysia) How the earth produces its magnetic field is a long-standing puzzle. Many theories have been proposed for the explanation of the earth's magnetic field. School of Physics- 2004 1 ADV L13 Earth’s Magnetic Field Lecture outline: The Earth as a magnet Strength of the Earth’s Magnetic Field Origin of the Earth’s Magnetic Field Solar Wind and Modification of Field Radiation Belts Aurora School of Physics- 2004 2 ADV. An Overview of the Earth's Magnetic Field. Contents. 1 Introduction. Geomagnetic field observations. Definitions. 2. 2 Observatories. Satellites. 2. 4 Other direct observations. Indirect observations. Characteristics of the Earth's magnetic field. Reversals. 3. 2 The present magnetic field. Westward drift. 3. Geomagnetic jerks. Crustal magnetic field. Field variations at quiet times.
Origin Of Earth Magnetic Field Pdf To WordField variations at disturbed times. The Earth's magnetic field as both a tool and a hazard in the modern world. Navigation. 4. 2 Directional drilling. Geomagnetically induced currents. Satellite operations. Exploration geophysics. Bibliography. 1 Introduction. The Earth's magnetic field is generated. Electrical. currents flowing in the slowly moving molten iron generate the magnetic. In addition to sources in the Earth's core the magnetic field. Earth's surface has sources in the crust and in the. The geomagnetic field varies on a range. The final section describes how the Earth's magnetic. First of. all, however, methods of observing the magnetic field are described. Declination, inclination. H is given by . The International System of Units (SI) unit. Tesla. At the Earth's surface the total intensity. T) to 6. 7,0. 00 n. T. Other units likely to. Gauss (1 Gauss = 1. T), the gamma (1 gamma. T) and the . The site of the observatory. The first category comprises variometers which make. A fluxgate sensor comprises a core of easily saturable. Around the core there are two windings. If an alternating current is. Both analogue and digital variometers require temperature- controlled. Even with these precautions they can still be subject to drift. The most common. types of absolute instrument are the fluxgate theodolite for measuring D and I and the proton precession magnetometer for measuring F. In the former the basic unit is an angle. The fluxgate sensor. Collimation errors. With the fluxgate sensor operating in null- field mode the. It can be seen that the spatial. Europe and a dearth elsewhere in the world, particularly in the ocean. Figure 1: Locations of currently. Back to the top of the page. Satellites. Since the 1. Earth's magnetic field. The first satellites. Satellites provide an excellent. CHAMP re- entered the Earth's atmosphere in September 2. The Swarm mission comprises 3 identical satellites. The CHAMP satellite sampled all local times in 4- 5. Two of the Swarm satellites fly side by side at altitudes (late 2. The lower two satellites are intended for very fine resolution of the magnetic field generated by the rocks in the Earth's crust. The upper satellite provides a simultaneous measurement at a different location. This is important for identifying magnetic fields generated by the magnetosphere and ionosphere. These are repeat stations and surveys made on. Repeat stations are permanently marked. Earth's magnetic. As a result they are flown at altitudes lower. Because of the difficulty in making accurately oriented. The surveys. were mainly over the ocean areas of the Earth, at mid to low latitudes. In a marine magnetic survey a scalar magnetometer is. Magnetic observations prior to the establishment. Gauss in the 1. 83. These are mainly of declination and. The subject of rock. From careful analyses of directions and intensities of rock magnetisation. These reversals occur slowly. In. addition to full reversals there have been many aborted reversals when. Earth's spin axis. The solid. inner metal core is thought to play an important role in inhibiting. At the present time we are seeing a 6% decline in the dipole. Whether this is a sign of an imminent reversal is. A solution to Laplace's. Gauss coefficients. There are internal. Earth respectively. A separation of the core and crustal fields. The internal field is often called the. The main- field coefficients change with. International Geomagnetic Reference. Field (IGRF) and the World Magnetic Model, this secular variation is. It has only been possible. Earth, largely by the ring current, since satellite data have become. At the Earth's surface the main field can. Earth's centre and tilted. However, significant deviations. Figures 2- 1. 1 show maps of declination, inclination. Generation IGRF model. Figure 2: Map of declination (degrees East or West of true north) at 2. Figure 3: Map of predicted annual rate of change of declination (degrees/year East or West) for 2. Figure 4: Map of inclination (angle in degrees up or down that magnetic field vector is from the horizontal) at 2. Figure 5: Map of predicted annual rate of change of inclination (degrees/year up or down) for 2. Figure 6: Map of horizontal intensity at 2. Figure 7: Map of predicted annual rate of change of horizontal intensity for 2. Figure 8: Map of vertical intensity at 2. Figure 9: Map of predicted annual rate of change of vertical intensity for 2. Figure 1. 0: Map of total intensity at 2. Figure 1. 1: Map of predicted annual rate of change of total intensity for 2. Back to the top of the page. Westward drift. Using direct observations of the magnetic. Earth's surface appears to be moving slowly westwards. This is particularly. Atlantic hemisphere at mid- and equatorial latitudes. It can be seen from this plot that there have. These sudden. changes are known as jerks or impulses and, at the present time, are. Some researchers. Figure 1. 2: Rate of change of declination at Greenwich (GRW). Abinger (ABN), Hartland (HAD), Eskdalemuir (ESK) and Lerwick (LER) observatories. Back to the top of the page. Crustal magnetic field. The field arising from magnetic materials. Earth's crust varies on all spatial scales and is often referred. A knowledge of the crustal magnetic field is. The anomalies seen at mid- ocean spreading. At these locations molten mantle. As new material is extruded, the existing crust is pushed away. Marine and aeromagnetic surveys. This discovery of a crude tape recorder of the Earth's. This variation is easiest. For this reason it is often referred to as the Solar quiet or Sq variation. Figure 1. 3 shows the actual variation in declination. Hartland observatory on June 2. This graph is typical. Sq variation seen at this latitude. Below this is the. Hartland over the same period. In reality. this type of variation in the geomagnetic field would affect the direction. Inclination. varies by less than a tenth of a degree and the total intensity of the. T, which represents. Earth's magnetic field strength at Hartland. Although. these effects are very small, they can be of interest to those who use. Earth's magnetic field as a tool for very precise. Figure 1. 3: Recorded daily variation in declination over one day at Hartland observatory. This regular fluctuation is caused by electrical. All currents, like those in wires, can only flow in. The copper used in wires conducts very well. However, in the ionosphere high energy. X- rays from the Sun displace electrons from (or ionise) the neutral (uncharged) molecules in the air to produce. Figure 1. 4, '+' and '- '. These charges allow the air to conduct. After dusk, in the absence of. This cycle. is repeated each day. Figure 1. 4: Effect of solar ultra- violet and X- ray radiation on ionospheric conductivity. The sunlight not only makes the air conduct, it also heats it causing. These winds combine with the tidal winds caused. Sun and Moon and the resulting thermo- tidal winds drive the ionospheric. This dynamo generates currents as the conducting ionosphere. Earth's magnetic field. These current systems. Figure 1. 5. Because it is solar radiation that produces the charges. Earth. It is these currents that produce the. Earth rotates beneath, which. The shape. size and location of these vortices also explain why the Sq variation. As the amount of solar radiation falling upon the. Sq variation also varies. Figure 1. 5: Ionospheric currents responsible for Sq variation during northern hemisphere. USGS). Back to the top of the page. Field variations at disturbed times. As well as the regular daily variation the. Earth's magnetic field also exhibits irregular disturbances, and when. These disturbances. Earth's magnetic field. The solar wind is a stream of charged. Sun and its pressure on the Earth's. Earth called the magnetosphere. When there is a disturbance in the solar. Figure 1. 6 shows a schematic. Earth's magnetosphere. Figure 1. 6: Solar wind and the Earth's magnetosphere. The amplitude of magnetic disturbances is. These collisions result in sometimes spectacular emissions. The prevailing conditions in the solar- terrestrial. Sun and their interaction with the Earth's magnetic field. There is presently some considerable interest. Sun and the solar wind are extremely valuable for this. Although irregular, magnetic disturbances. The main pattern. Figure 1. 7 shows. Another important pattern is the 2. Sun. as seen from Earth. Figure 1. 7: The annual number of. Superimposed. is the smoothed sunspot number. The dashed lines indicate solar minima. Note the correlation of. Back to the top of the page. The Earth's magnetic field as both a tool and a hazard in the. Navigation. The earliest writings about compass navigation. Chinese and date from 1. A. D. In 1. 70. 0 the first magnetic chart, covering. Atlantic Ocean, was produced by Halley. Contemporary values of declination, or for. These values must be kept up- to- date by regular. This is an example. Earth's magnetic field being a tool. There are two main methods of navigation. One method makes use of gyro tools but this can. The other method makes use of magnetic tools. As accuracy. is critical for economic reasons and to avoid well collisions, the accuracy. Earth's magnetic field values, used to correct the. To attain these accuracies. This application is an example of the Earth's magnetic field. In particular, the power transmission system in Quebec, Canada. Other effects such as increased corrosion. This is an example of the Earth's magnetic. The orbit. of the satellite can be changed and sometimes expensive manoeuvres must. Other effects on satellites are caused by radiation. The prediction of magnetic. This is another example of. Earth's magnetic field being a hazard in the modern world.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
December 2016
Categories |