The recent changes in Earth’s magnetic field

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New data from Europe’s Swarm constellation of satellites detail the recent bigger-than-expected changes that have been occurring in the Earth’s magnetic field.

Data from Swarm, combined with observations from the CHAMP and Ørsted satellites, show clearly that the field has weakened by about 3.5% at high latitudes over North America, while it has strengthened about 2% over Asia. The region where the field is at its weakest – the South Atlantic Anomaly – has moved steadily westward and weakened further by about 2%. These changes have occured over the relatively brief period between 1999 and mid-2016.

It was already known that the field has weakened globally by about 10% since the 19th century. These changes appear to be part of that generally weakening. Some scientists have proposed that this is the beginning of an overall flip of the magnetic field’s polarity, something that happens on average about every 300,000 years and last occurred 780,000 years ago. At the moment, however, we have no idea if this theory is correct.



  • Steve Earle

    Interesting. When it does happen does anyone know if the magnetic poles will simply reverse, but stay somewhat in the vicinity of the geographic poles, or could they wind up near the equator for example?

  • Edward

    Steve Earle,
    In the past, they have reversed it the vicinity of the geographic poles, but at least some models show that the process generally takes centuries/millennia, and that during the reversal process there may be temporary north and south magnetic poles popping out arbitrarily in several places around the globe, even at the equator. Compass navigation may be tricky or useless during the transition.

    I usually use wikipedia to remind me of what I already knew, and this entry says mostly what I remember on the topic, and it includes a nice graphic in the next section:

  • LocalFluff

    I wonder if this could have an influence on the climate. Weaker magnetic field means more ionizing radiation hitting the lower atmosphere, creating more condensation nuclei for cloud formation, and more clouds reflect more sunlight lowering the average global temperature. Analogue to how the Solar magnetic field strength affects cloud formation (in theory).

    More CO2, which we have, in itself (ceteris paribus) causes increased temperatures. But many other factors are involved in a climate too, and maybe this is yet one of them. 2% weakening since the “hiatus” began sounds pretty significant.

  • Steve Earle

    Thanks for the added info Edward, very interesting! Especially when considering Compass Navigation.

    I wonder how shifting magnetic poles would affect the GPS system? My first thought would be no effects since the GPS system relies on super-accurate clocks, not compasses.

    But on second thought what do the GPS satellites rely on to stay oriented and in one position relative to the Earth? Do they use Guide Stars and Gyroscopes only? Will a fluctuating magnetic cause any issues?

    I ask these questions because if compasses become close to useless, then GPS and similar systems become even more important than they already are.

  • Edward

    Steve Earle asked: “what do the GPS satellites rely on to stay oriented and in one position relative to the Earth? Do they use Guide Stars and Gyroscopes only? Will a fluctuating magnetic cause any issues?

    GPS satellites orbit closer to the Earth than geostationary orbit, about 12,500 miles for the US version, so they do not stay in one position relative to the Earth. Like most satellites, they use guide stars with a unit called a star tracker, which provides orientation information. Gyroscopes are also often used along with the data from star trackers.

    To stay pointed at the Earth, satellites often use Earth sensors or horizon sensors to verify the direction to the Earth. They may use sun sensors to verify the direction to the sun, so that they can be sure that their solar arrays are pointed in the right direction.

    I don’t know whether GPS uses a Moon sensor, but one could be used to verify the position around the Earth.

    As for issues from a fluctuating magnetic field, I think it will not cause any navigational issues, but the Earth’s magnetic field protects satellites from such things as ion storms (coronal mass ejections), which can cause problems for satellites that are not built for such problems, as happened to Telstar 401 in 1997. If the field is weakened, then Earth-orbiting satellites may have to be hardened like the deep space probes are.

  • Steve Earle

    Thanks again Edward! I had forgotten that the GPS Sats were not in GeoSync Orbit. It sounds like we will be able to rely on GPS when magnetic compasses start acting funny.

    It looks like we may have invented GPS just in time, Geo-Historically speaking of course ;-)

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