Is there a difference in Earth's magnetic field between day and night?

Magnetic Field

  • $\begingroup$ Why would there be a difference in the magnetic field between day and night? $\endgroup$
    – VinalV
    Jul 29, 2022 at 1:24
  • $\begingroup$ @VinalV wrong question, sorry. The way my mind understands what a magnet is, is out of this world... $\endgroup$
    – Origin
    Jul 29, 2022 at 1:46
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    $\begingroup$ the question is ambiguous. Obviously, there is no effect on the surface (we would had heard about day compasses vs night compasses since circa 1492, and we haven't). Ever since van Allen and space/craft, we know the solar wind blows the earth's field to larger heliocentric radii, completely distorting the dipole shape in space. Larger heliocentric radii are the same direction as "night" on Earth, so perhaps the answer is "yes". Finally, why would you expect a difference? "idk, the ionosphere is diurnal?" is not a brilliant response, but it's legit for an inquisitive student. $\endgroup$
    – JEB
    Jul 29, 2022 at 2:15
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    $\begingroup$ With the way JEB puts it, if given a better question structure there certainly is an interesting question in here somewhere. It needs a lot of editing maybe to bring it out though. $\endgroup$
    – Triatticus
    Jul 29, 2022 at 2:24
  • $\begingroup$ @JEB i don't think a compass is sensitive enough to measure the expected day/night difference. $\endgroup$ Jul 29, 2022 at 12:36

2 Answers 2


It looks like there is some difference between day and night geomagnetic field, and one of the causes is mentioned in @JEB's comment.

Yamazaki Earth, Planets and Space (2022) 74:99

The Earth’s upper atmosphere is weakly ionized, as it receives energy inputs from the Sun in the form of electromagnetic waves. Ionized particles interact with neutrals by collisions and move through the ambient geomagnetic field, which gives rise to an electromotive force to support electric fields and currents. The process is known as the ionospheric wind dynamo, or simply ionospheric dynamo, and it is the dominant production mechanism of ionospheric electric fields and currents at middle and low latitudes during geomagnetically quiet periods (e.g., Richmond 1995a; Heelis 2004). The dynamo currents flow mainly on the dayside at E-region altitudes (ca 90–150 km), where the electrical conductivity of the ionosphere is greatest. At night, the ionospheric conductivity is smaller by about two orders of magnitude (e.g., Richmond 2011). Thus, the currents are also much weaker and have a negligible efect on the geomagnetic feld on the ground. The daytime presence and nighttime absence of the magnetic effect associated with ionospheric dynamo currents lead to daily variation of the geomagnetic field measured at ground stations. Geomagnetic daily variation is smooth and regular in appearance on geomagnetically quiet days when high-frequency geomagnetic disturbances associated with geomagnetic storms and substorms are absent, and is often referred to as solar-quiet (Sq) variation (e.g., Campbell 1989; Yamazaki and Maute 2017)."


Solar wind is constantly out-flowing from the sun. That wind distorts the Earth's magnetosphere by compressing it on the windward (day) side and elongating it on the downwind (night) side. As a result, the shape of the magnetosphere looks like a teardrop when observed from space at a position above the terminator.

During times when the solar wind increases, like when there is a solar flare, that elongation becomes more exaggerated until it can no longer sustain itself. At that point, just like a slingshot that has been pulled back and released, the magnetic field lines compress on the downwind (night) side forcing ionized particles into the atmosphere resulting in an aurora borealis. In the opposite direction, a jet of plasma is released into space in the downwind direction. This is called "plasma farting" by the scientific illuminati.

Ok, I made that last sentence up. But, the rest of it is accurate.

  • $\begingroup$ Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. $\endgroup$
    – Community Bot
    Aug 3, 2022 at 21:20
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    $\begingroup$ Yes, it could be improved but it doesn't need to be improved. It's common knowledge if you're a geophysicist. $\endgroup$
    – barmid
    Aug 3, 2022 at 21:49

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