If you take a modern compass with a magnetic needle, you will find that needle points in N -direction. Don't you ever think why this occurs? Okay, today I want to let you know through this post that, the North Pole, that needle point is not Earth's geographic north pole but it is Earth's magnetic north pole. You see! Our planet Earth has some magnetism that assists in a such orientation. Without waste time, I have described to you here down in a simplified way about these fields.
Earth's (Geo) Magnetic field at or near the surface of the Earth originates largely from within and around Earth's core. It is revealed that due to polarity attraction the magnetic North Pole of the Earth corresponds to South Pole of the freely suspended bar magnet and vice versa is true as shown in the figure below.
Fig: Simple Earth's Magnetic field representation
Also geomagnetic field may be contributed by
- Steady state magnetization of crustal rocks.
- Current induced by the External field variation
What are some simple evidences supporting the presence of Earth's magnetic field?
- The freely suspended magnetic compass become attracted and pointing towards N - S direction.
- The deep buried iron material in the ground become magnetized naturally.
Principal Components (elements) of magnetic field used to describe the geomagnetic field.
- Declination (D)
- Inclination (I): Horizontal and Vertical Components
- Total Intensity (F).
Fig. Components of magnetic field
Declination (D): Angle between magnetic meridian and geographic meridian.
Inclination (I): Angle at which magnetic rector dips below the horizontal.
It is -90° at geomagnetic south pole
It is +90° at geomagnetic North pole
It is 0° at the Equator.
Representation of Magnetic Vector
Magnetic vector can be described by either in
i/ The cartesian system
Such as ( X, Y, Z) for North, East and Vertical downward respectively
ii/ Spherical polar system
Such as (F, D ,I) for Total intensity, Declination, and Inclination respectively.
How they are related, H = FcosI and V = FsinI
X = HcosD ........ Northward
Y = HsinD .........Eastward
TanI = Z/H
Since TanD = Y/X
The Resultant Force / Total Intensity (F)
F2 = H2 + V2 + Z2
or F2 = X2 + Y2 + Z2.
Then,
F = √(H2 + V2 +Z2 / X2 + Y2 + Z2)
Components of Earth's Magnetic field.
Here it described components of geomagnetic field from internal origin.
i/ Main - dipole field
ii/ Non - dipole field
MAIN DIPOLE FIELD
It behaves to first order approximations.
Geomagnetic poles: Are positions on the Earth's surface through which the axis of the best fitting dipole passes. They are located in Hayes Peninsula in North Greenland and near the Russian Vostok research station in greater Antarctica.
Dip poles or Magnetic poles: Are located where magnetic field is directed vertically.
NON - DIPOLE FIELD
Are obtained by minus the field of the inclined geocentric dipole from total Field.
It is about 5% of total field.
Secular Variation
The term originated from latin word "saeculum" means for a long age.
It involves slow but progressive change in field intensity and westward drift in direction.
They are manifest as variations of both dipole and Non - dipole components of the fields.
Geomagnetic field is produced by Electric current induced within the conductive liquid outer core as a results of slow convective movements within it. Liquid core behaves as a Geodynamo.
Possible sources
1: Permanent magnet
Due to dipole magnetic of the Earth.
- Materials in the crust can be magnetized at temperature lower than curie point.
- It can not account for the observed Earth's magnetic field as it require the crust to have 50% magnetite to account.
2: Rotating Body
Gilbert, It Rotates because it is magnetic and magnetic because it rotates around its axis.
P.M Blackett, existed any rotated body intrinsic magnetized.
3: Electric Current
By coupling movement of convective currents in the core.
Factors important in generation of magnetic field in the Earth's core.
- Temperature differences: The temperature difference between inner core and outer core of the Earth play an important role in triggering of Convective currents flows within the Earth, which in turn results in generation of magnetic field.
- Viscosity: high viscous of molten materials in core may cause and increases chaotic flows of induced electric currents which in turn may results in magnetic fields.
- Electrical Conductivity: As the current flows easily in molten core fluid, it produces magnetic field by self magnetization due to repetitive flows.
Generally, Earth's Magnetic fields plays a vital role in protecting us and our atmosphere from very fast and energetic charged particles (radiation) from the sun / space. That, if these charged particles would be allowed to reach us they would cause lethal effects (skin cancer), blow out any gases from atmosphere, hence our life on this planet would be faced with serious problem even would be impossible.!
Thanks for your time!
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