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geomagnetism

The mysterious ways of geomagnetism

One fallout from the United States (US) government shutdown was a delay in updating global navigation systems. Many navigational systems, starting with the humble compass, are anchored to the Magnetic North Pole (MNP).

geomagnetism

What is the issue?

  • The MNP shifts and it’s necessary to reorient the position of the MNP, every five years or so. The next update was due in 2020.
  • But MNP has shifted so much in the last four years, an emergency update was in progress when the US government shut down.

Details –

  • The Earth is a roughly spherical body, spinning west to east. The geographic North Pole is the northernmost point of the axis on which it spins and the geographic South Pole, the southern-most.
  • Maps use a grid marked with lines circles of longitude and latitude. There are 360 circles of longitude, each joining the geographic North and South Poles, with Greenwich Observatory, the UK as the zero-point.
  • There are 90 circles of latitude running east-west, with the equator as zeropoint. Each circle is further sub-divided into minutes and seconds (navigation systems use decimals). Every spot on the Earth’s surface has coordinate references.

Role of magnetic fields –

  • There is no easy way to locate the geographic poles. But the Earth has a strong magnetic field.
  • The northern point at which the magnetic field “dips” into the Earth is the MNP (ditto for the Magnetic South Pole or MSP).
  • Compasses point along the axis of the line joining the MNP and MSP.
  • A magnetic needle points towards the MNP, except when it’s actually at the MNP, when it will point straight down into the Earth.
  • The MNP (actually a large area, not a point reference) is therefore, used as an anchor for mapping.
  • If we know where the MNP is, in relation to the geographic north pole, navigational accuracy is possible, using even a simple compass.
  • A compass points to the MNP and, if we know the degree of difference between MNP and North Pole (the “magnetic declination”), we can calculate the location.

How magnetic fields are formed?

  • The magnetic field is believed to be caused by flows of molten iron, and other metals with magnetic properties, deep inside the Earth.
  • Those flows generate electric currents, which cause the Earth’s geomagnetism.
  • But as liquid metal flows, it causes the magnetic poles to wander around.

Need for reorientation –

  • The MNP’s shifts require regular position updates and the shifts have, for unknown reasons, been accelerating.
  • The MNP is moving at about 55 km per year. It is currently about 10 degrees south of the geographic North Pole, somewhere in the Arctic Ocean
  • It was in Northern Canada when it was first mapped in the 1830s, and it is now headed towards Siberia, moving northby north west. It crossed the international dateline in 2017.

The current concern –

  • The World Magnetic Model (WMM) as it is called, was scheduled for an update on January 15. That update was finally released on February 4, after delays caused by the shutdown.
  • The WMM is maintained by the United States’ National Geospatial-Intelligence Agency and the United Kingdom’s Defence Geographic Centre.

What is WMM?

  • The WMM is a predictive model. It estimates likely MNP movement across the next five years. It was developed jointly by the US National Geophysical Data Center and the British Geological Survey.
  • The WMM is used by defence forces, and for commercial sea and air navigation, surveying and mapping systems, satellite tracking, commercial GPS services and to help telecom networks derive location data for users.

Effect on GPS –

  • GPS bounces signals from three or four satellites off a given spot and exactly locates it by calculating the delays in each signal.
  • So GPS itself doesn’t need magnetic data. But it can’t tell the direction in which a car, ship, or drone, is heading. That’s why WMM references are useful for navigation.

Effect on environment –

  • Many animals and birds use geomagnetism to orient themselves.
  • Migratory birds, bats, butterflies use the geomagnetic field and so do dolphins and whales.

SourceBusiness Standard

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