Prof. Richard Holme - Research Interests

Excursions and Reversals - The Geomagnetic field is (probably) not reversing

The strength of the magnetic dipole is currently dropping: this has been observed throughout the time of measurement (since 1833), and palaeomagnetic measurements suggest it has been falling for over 1000 years. This has often been used to claim we are entering a magnetic reversal. The fall of the field strength is closely related to a growing weakness in the field, the so-called South Atlantic Anomaly (SAA). However, a high-quality model of the last geomagnetic excursions (times when the field drops in strength, and changes significantly in direction) suggest this might not be the case. The structure of the field changes do not mimic the growing SAA; however, the modelling has relieved other times (particularly around 46,000 years bp) at which a very deep SAA appears, but the field then recovers to normal structure. The evolution of this feature is also matched by strong features in the berrylium and chlorine isotope records, providing independent evidence of its occurance. This changes suggest that, despite the current fall in field strength, we are not entering an excursion (or even a reversal), but the growing SAA is instead part of the normal evolution of the secular variation: it is most likely that the field strength will recover. For more details, see the publication in PNAS (link for those with PNAS access), https://doi.org/10.1073/pnas.1722110115, led by Max Brown, a former student. I am not allowed to provide a free link to the paper, but a link to a preprint will be provided.

Planetary Magnetism

Methods applied to modelling the geomagnetic field (see below) are also extremely useful in modelling the fields of other planets, which in turn give us strong constraints on the underlying dynamo process. Of most interest at the moment is the field of Jupiter, due to the arrival of the Juno mission. In preparation for this mission, a recent student, Dr. Victoria Ridley, updated models of Jupiter considering data from all available missions to date. Her thesis is available from the University of Liverpool repository, and it has yielded a paper (DOI: 10.1002/2015JE004951) (now open access) in JGR planets. She determined models of the secular variation (field variation in time) for test against results conclusions from the Juno mission. (Note that there are some mistakes in the models listed in the thesis; the paper is now correct.) Models are presented in the paper, and also available here as excel file and pdf file (the latter will produce a usable text document). These are constant with time, linear with time (constant secular variation) and linear with time allowing for a change in reference frame rotation. The studentship was funded through the Leverhulme Trust.

New data have also been obtained for Saturn from the close-approach passes from the end of the Cassini mission. I am also part of the magnetometer team for the JUICE mission, which will make detailed observations of Jupiter, and provide magnetic measurements of its moons, particularly Ganymede. Sadly, these extremely exciting data are likely to be available in 2033.......

Earth Rotation and Geomagnetism

There is a strong link between studies of Earth's length of day (its rotation speed) and geomagnetic processes. In particular, decadal variations are thought to originate from the exchange of angular momentum between the solid Earth and the fluid core. Subdecadal variations have been less clear; however, my recent work has strongly clarified these issues, in particular links to so-called geomagnetic jerks. A Nature paper (link for those with Nature access) on this has been published; I am not allowed to provide a free link to the final paper here, but for those without Nature access, I am allowed to present the final submitted version (or you can email me here for a reprint).

I also gave a talk on this subject at the Royal Astronomical Society which the RAS provide online, so if you want to see me talk about the work, see here.

And on a rather different subject, over historical periods, length of day variation is constrained by eclipse observations. I was interested in observations reported for the Isle of Man. Unsurprisingly, my interest provided no new geophhysical constraint (the data had been examined many times, and found to be of insufficient quality for use). However, it did lead me consider what our knowledge of length of day variation can yield concerning the historical sources. If interested, I wrote a rather self-indulgent paper on the subject for Isle of Man Studies.

Deep Earth Structure and Processes

The aim of my work is to obtain a better understanding of the evolution and processes in the deep Earth. The community considering the broader aspects of this work is SEDI -- Study of the Earth's Deep Interior. I recently organised a UKSEDI meeting through the Royal Astronomical Society. For a record of this meeting, click here.

It isn't my work, but I ended up talking about some very-deep-Earth results recently on CBBC Newsround, which I can't resist giving a link to here - run the movie at the top of the article.

One of the questions I am asked most often is "Is the magnetic field reversing?", and if so "Are we all going to die?" The answers are "we don't know", and "yes, but it has nothing to do with what the magnetic field does"! The best popular treatment of this that I know of is a Channel 4 / WGBH presentation over 10 years old now, entitled "Magnetic flip" ("Magnetic storm" in the US). You can still view this on YouTube here. This has a fairly standard science documentary format - before you get too worried, pay careful attention to the final 5 minutes!

Satellite Geomagnetism

Low Earth orbiting satellites provide excellent global coverage of the large-scale magnetic field. I have a primary interest in the modelling (and modelling methodology) of the internal geomagnetic field, particularly from past involvement with the satellite geomagnetism group at GFZ related to the calibration of the vector magnetic experiment on the satellite CHAMP. Current developments in this area focus on the ESA mission Swarm. I was a partner in the GEOSPACE consortium (Geomagnetic Earth Observation from Space), which investigated all aspects of satellite magnetism, including the internal field, the ionospheric and magnetospheric fields, and the field from ocean induction, and particularly how the modelling process is complicated by the presence of multiple field sources.

Main Field and Core-Flow Modelling

A basic description of main field modelling, and how it can be used to probe core processes, is here

The Lithospheric Field

Magnetic satellites also provide unparalleled information on the long wavelength lithospheric field

The Palaeomagnetic and Archaeomagnetic Field

I am part of the Geomagnetism group, whose principal interest is the behaviour of the magnetic field as discernable in archaeological artefacts and rocks. My primary interests are in the past modelling of the geomagnetic field, both on archaeomagnetic time scales for dating purposes, and on longer time scales, particularly modelling magnetic reversals. Although not involved in measurement myself, I have strong links with colleages involved in data collection, with particular interest in Southern hemisphere data.

A list of my publications (recent and back to 2000) can be found at my University staff page. A few of my publications can be found here

Richard Holme (holme@liv.ac.uk)

  • School of Environmental Sciences
  • University of Liverpool