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The magnetic field is generated by a feedback loop: current loops generate magnetic fields (Ampère's circuital law); 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). [58]
Magnetometry is the process of measuring changes in the Earth's magnetic field. [15] The outer layer of the Earth's core is liquid and mostly made up of magnetic iron and nickel. [16] When the Earth turns on its axis, the metals release electrical currents which generate magnetic fields. [17] These fields can then be measured to reveal ...
According to the BBC, the "global map shows the variation in strength of the magnetic field after the Earth's dipole field has been removed (Earth's dipole field varies from 35,000 nano-Tesla (nT) at the Equator to 70,000 nT at the poles). After removal of the dipole field, the remaining variations in the field (few hundreds of nT) are due to ...
However, due to extraordinarily large and erratic movements of the north magnetic pole, an out-of-cycle update (WMM2015v2) was released in February 2019 [4] (delayed by a few weeks due to the U.S. federal government shutdown) [5] to accurately model the magnetic field above 55° north latitude until the end of 2019. The next regular update ...
On nautical charts, the top of the chart is always true north, rather than magnetic north, towards which a compass points. Most charts include a compass rose depicting the variation between magnetic and true north. However, the use of the Mercator projection has drawbacks. This projection shows the lines of longitude as parallel.
Magnetic surveys discovered linear magnetic anomalies that in many areas ran parallel to an ocean ridge crest and showed a mirror-image symmetrical pattern centered on ridge crests. [21] Correlation of the anomalies to the history of Earth's magnetic field reversals allowed the age of the seafloor to be estimated. [22]
Because the Earth's field vector is much stronger than the anomaly field, a modern magnetometer measures the sum of the Earth's field and the component of the anomaly field in the direction of the Earth's field. Sections of crust magnetized at high latitudes have magnetic vectors that dip steeply downward in a normal geomagnetic field.
Magnetic declination varies both from place to place and with the passage of time. As a traveller cruises the east coast of the United States, for example, the declination varies from 16 degrees west in Maine, to 6 in Florida, to 0 degrees in Louisiana, to 4 degrees east in Texas.