Instabilities of the Earth’s magnetic field over multi-millennial timescales

Earth’s magnetic field varies over a wide range of time scales. The very long multi-millennial scales are associated with variations of the internal core field. The short timescales, annual and shorter, are related to field contributions generated by current systems in the ionosphere and magnetosphere. The most dramatic changes occur at the longest periods, namely geomagnetic reversals and excursions. They represent a significant decrease in the field intensity, with reversals having a complete polarity flip and longer duration in contrast to excursions. While the reversals are global events, the excursions can be of global and regional nature. For the latter, only part of the Earth is affected with very low intensity and transitional directions. The last geomagnetic reversal, Matuyama-Brunhes, happened 780,000 years ago, and the last global excursion, the Laschamps excursion, occurred 41,000 years ago. These events are studied with indirect measurements, paleomagnetic data from sedimentary cores and volcanic rocks. Global data compilations enable us to reconstruct the field’s spatial and temporal variations and to better understand the core processes responsible for these variations.

Magnetic field lines during a period of high dipole moment, for example 1900 AD (top) and the Laschamps geomagnetic excursion, 41,000 years ago (bottom). The figures show the dipole-dominated structure at stable periods and very complex, multipolar structure of the magnetic field in transitional epochs. The color maps represent the radial field component at the Earth’s surface. The blue lines are pointing inward and red lines in an outward direction.

Credit: Maximilian Schanner, GFZ Potsdam, 2022. https://sec23.git-pages.gfz-potsdam.de/korte/pymagglobal-3d-fieldlines/

doi: 10.5880/GFZ.2.3.2020.005

While the current configuration of the geomagnetic field can be approximated with a dipole (having two poles, magnetic north and south pole), during geomagnetic excursions, the dipole is not a dominant component. The figures present the magnetic field lines of a dipole vs. non-dipole-dominated field, where the former is characteristic of the present-day and the latter of the Laschamps excursion. Over very long time scales, tens of thousands to millions of years, the field closely approximates a geocentric axial dipole. This hypothesis allows using the paleomagnetic data for reconstructing plate tectonics.

Direct observations indicate that the magnitude of the Earth's magnetic axial dipole has decreased since 1840, and predictions of geomagnetic secular variation show that it will likely continue to decrease over the following decades. A weakened geomagnetic field may lead to numerous hazards like satellite outages, disturbances in communications and navigation, and induced currents in pipelines and transmission lines. The following questions come naturally:

Will the geomagnetic field go through an excursion or a reversal in the future? Most probably yes, considering the dynamic nature of the field and the frequency variations of these transitional events.

Is the geomagnetic field heading towards an excursion or reversal now? Probably not, based on analyses of available paleomagnetic field models covering the past 10,000 and 100,000 years and the fact that the field at present seems to be clearly stronger than the long-term average.

Can we predict such events? No, this remains an open question because it is hard to foresee the long-term changes. The geomagnetic field intensity needs to decay further for several centuries to recognize and distinguish a future transitional event from normal secular variation.

Sanja Panovska is a postdoctoral researcher at the Helmholtz Centre Potsdam – GFZ German Research Centre for Geosciences. Her primary research focus is reconstructing the long-term evolution of the geomagnetic field based on paleomagnetic data over different timescales from the Holocene, to 100,000 years and over the Earth’s geological history. She is also involved in studies on productions of cosmogenic isotopes, paleomagnetosphere and paleoaurora.

'Geoscience Connections' on YouTube!

The joint IAGA-IASPEI proposal awarded by IUGG consists of a documentary, web series and short movies about the science and the scientists of the 8 different IUGG associations and the connections between them.

While the documentary and web series will be released later on, the short movies of the scientists and early career researchers from the different associations are now being released on IUGG and IAGA YouTube channels!

Every Tuesday and Friday, a video will be published which would include an introduction about the researcher followed by a description of the science they do. The videos, less than 5 minutes in length, have been aimed at the general public and early career researchers. For some weeks, an additional video about science outreach will also be made available.

Have a look here and head over to our YouTube for more!

Keep a look out at our social media channels for upcoming videos.

Imposter syndrome in research

Imposter syndrome is the inability to accept that your accomplishments are a result of your hard work and abilities. Or in other words, you are a researcher.

Here are some of the simplest tests to check if you have the syndrome-

    1) You think you don't know any/many things but have become good at pretending that you do.

    2) Somebody said you don't deserve it and it stayed with you. 50 others said the opposite but you think they are just being nice or don't know anything.

    3) You are reading this.

"Piled Higher and Deeper" by Jorge Cham
www.phdcomics.com

If it has been established that you are an imposter in your eyes, I have a few things to say.

    1) Talk to your peers. Most often others are thinking the same thing but nobody has the courage to speak it out loud or discuss.

    2) But keep in mind, nobody has been through what you have been through. Sure, everybody has had their own struggles but that doesn't make their or your struggle more or less difficult. Your thoughts can differ and thats okay.

    3) Feelings can't be measured. Feelings are different for different people for different things. They can also be similar but don't try to find a way to normalise them.

    4) You need to accept the advice you give others.

    5) Reach out. To anyone or everyone. You might end up helping someone else when you were just looking for it yourself.

At the end of the day, it's okay to have imposter syndrome if its not affecting you strongly. Sometimes, it helps you to do better. But if its consuming your thoughts too much, ask for help. Especially for early career researchers, it would be great if mentors and supervisors could make sure the student is comfortable being themselves and can ask for help whenever needed, personally or professionally.

Shout out in the comments if you would like to read more such thoughts and blogs from researchers at different levels of their careers. Or if you'd like to ask or reach out for support.

---

Shivangi Sharan is a postdoctoral research associate at Imperial College London, working on prioritising the research that will be carried out using the JUICE magnetometer data. Previously, she has worked on the interior of Mars and Jupiter using their magnetic observations. She is an active member of the IAGA Blog Team and can be contacted via e-mail here.

---