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.
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
(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
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
for a reprint).
I also gave a talk on this subject at the
Royal Astronomical Society
which the RAS now provide online, so if you
want to see me talk about the work, see
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. 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
here. This has a fairly standard science documentary format - before you get too
worried, pay careful attention to the final 5 minutes!
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
related to the calibration of the vector magnetic experiment on
Current developments in this area focus on the ESA mission
I was a partner in the
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
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
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.
I welcome applications for PhD study, both as part of our yearly
allocation of NERC funded UK studentships, and from candidates who may be
able to attain independent funding
(for example, from a Commonwealth
scholarship, or the Petroleum Development Fund).
A primary area of interest is the extension and implications of my
recent discoveries on links between
Earth rotation and geomagnetism.
One additional area of interest to me is the
study of quiet-time geomagnetic variation (for example, Sq and the
Equatorial Electrojet), with applicants strongly encouraged
from countries (e.g., India,
Nigeria) with a strong local tradition of work in these areas.
I am also always interested in students wishing to work in
better understanding of the Earth's core, particularly core flow
and core-mantle interactions. Such projects would particularly
suit students with a physics background.
For some ideas of possible areas of study, see also
Dynamics and Implications of Geomagnetic Field Variations: Signal
extraction from 150 years of Geomagnetic observatory 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