Earth magnetic field

PREPARED BY

CHELANI PRASHANT A

EARTH MAGNETIC FIELD

EARTH MAGNETIC FIELDintroduction

Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from the Earth's interior out into space, 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 microteslas (0.25 to 0.65 gauss).

The North geomagnetic pole, located near Greenland in the northern hemisphere, is actually the south pole of the Earth's magnetic field, and the South geomagnetic pole is the north pole. Unlike a bar magnet, however, Earth's magnetic field changes over time because it is generated by a geodynamo

The North and South magnetic poles wander widely over geological time scales, but sufficiently slowly for ordinary compasses to remain useful for navigation. The magnetosphere is the region above the ionosphere and extends several tens of thousands of kilometers into space, protecting the Earth from the charged particles of the solar wind and cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects the Earth from harmful ultraviolet radiation.

William Gilbert and the Birth of Magnetism

Personal Physician to Elizabeth I

Published De Magnete in 1600, a 6-volume treatise documenting his experiments with magnetism

Proposed that Earth behaves like a giant bar magnet

Died in 1603 of bubonic plague William Gilbert, 1544-1603

At any location, the Earth's magnetic field can be represented by a three-dimensional vector.. Its angle relative to true North is the declination (D) or variation. Facing magnetic North, the angle the field makes with the horizontal is the inclination (I) or magnetic dip. The intensity (F) of the field is proportional to the force it exerts on a magnet. Another common representation is in X (North), Y (East) and Z (Down) coordinates

INCLINATION

angle measured from horizontal angle measured from geographic north

DECLINATION

intensity

The intensity of the field is often measured in gauss (G), but is generally reported in nanoteslas (nT), with 1 G = 100,000 nT. A nanotesla is also referred to as a gamma (γ).The tesla is the SI unit of the Magnetic field, B. The field ranges between approximately 25,000 and 65,000 nT (0.25–0.65 G). By comparison, a strong refrigerator magnet has a field of about 100 gauss (0.010 T).

Dipole model of the Earth's magnetic field

The dipole model of the Earth's magnetic field is a first order approximation of the rather complex true Earth's magnetic field. Due to effects of the interplanetary magnetic field, and the solar wind, the dipole model is particularly inaccurate at high L-shells (e.g., above L=3), but may be a good approximation for lower L-shells. For more precise work, or for any work at higher L-shells, a more accurate model that incorporates solar effects,

MAGNETOSPHERE Solar wind = charged particles ejected from the Sun

Magnetosphere = a zone of charged particles trapped by Earth’s magnetic field

Magnetotail = portion of a magnetosphere that is pushed away from the sun by the solar wind

EARTH'S CORE AND THE GEODYNAMO

The Earth and most of the planets in the Solar System, as well as the Sun and other stars, all generate magnetic fields through the motion of electrically conducting

The mechanism by which the Earth generates a magnetic field is known as a dynamo.

The magnetic field is generated by a feedback loop: current loops generate magnetic fields a changing magnetic field generates an electric field (Faraday's law) and the electric and magnetic fields exert a force on the charges that are flowing in currents (the Lorentz force).

In 1995, the first computer model was published (Glatzmaier-Roberts model) which successfully simulated the geodynamo, including spontaneous reversal Since then, several other groups have also succeeded

Computer Model of the Geodynamo

MEASUREMENT AND ANALYSIS

The Earth's magnetic field strength was measured by Carl Friedrich Gauss in 1835 and has been repeatedly measured since then, showing a relative decay of about 10% over the last 150 years. Governments sometimes operate units that specialize in measurement of the Earth's magnetic field. These are geomagnetic observatories, typically part of a national Geological survey, for example the British Geological Survey's Eskdalemuir Observatory

Example of analysis

BIOMAGNETISM

Animals including birds and turtles can detect the Earth's magnetic field, and use the field to navigate during migration. Cows and wild deer tend to align their bodies north-south while relaxing, but not when the animals are under high voltage power lines, leading researchers to believe magnetism is responsible.

Researchers found out that very weak electromagnetic fields disrupt the magnetic compass used by European robins and other songbirds to navigate using the Earth's magnetic field. Neither power lines nor cellphone signals are to blame for the electromagnetic field effect on the birds,.

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