- Data-based modeling of the Earth's magnetic field
- Geomagnetic secular variation, especially at subdecadal time scales
- Geomagnetic Sq field and the equatorial electrojet
- Crustal magnetic anomalies
- Geomagnetic observation techniques (satellites, observatories, crowdsourcing, etc.)
My current research focuses on improving the spatio-temporal description of the Earth's magnetic field by data-based models such as the Enhanced Magnetic Model (EMM) and the High Definition Geomagnetic Model (HDGM), with the aim of improving navigational accuracy. Our approach is to first develop research models describing the magnetic field generated by a single source, for example the Earth's core or the electrical currents in the magnetosphere, and then combine these models into composite models describing the field from several sources. When a composite model is mature enough, we transition it to operations through NCEI. Besides being of practical use, geomagnetic models are also valuable tools to investigate the various physical processes at the origin of the Earth's magnetic field and its variations. Better understanding of such processes in turn leads to better models.
Selected recent projects:Rapid geomagnetic variations of internal origin
The geomagnetic secular variation, which originates within the Earth's liquid outer core, has long been known to undergo sudden changes in its trend, i.e., the second derivative of the field changes sign. Such events, referred to as geomagnetic "jerks", were thought to occur irregularly in time. We have recently shown that "jerks" since 2000 were in fact caused by a series of large-scale pulses in the core magnetic field. These pulses have occurred every three years since 2006. They could be detected by directly modeling the second order time derivative of the field, i.e. the secular acceleration, from satellite data. We further proposed an interpretation of such pulses in terms of Equatorial Magnetic Rossby waves, a type of waves theoretically predicted in the 1980s but never observed before. Progress toward understanding "jerks" and pulses could lead to better predictions of the secular variation in models such as the World Magnetic Model (WMM) or the International Geomagnetic Reference Fied (IGRF).
Chulliat, A., P. Alken and S. Maus, Fast equatorial waves propagating at the top of the Earth’s core, Geophys. Res. Lett., 42, 33213329, doi:10.1002/2015GL064067, 2015.
Chulliat, A., and S. Maus, Geomagnetic Secular Acceleration, Jerks, and a Localized Standing Wave at the Core Surface from 2000 to 2010, J. Geophys. Res. Solid Earth, 119, doi:10.1002/2013JB010604, 2014.
Chulliat, A., E. Thebault and G. Hulot, Core field acceleration pulse as a common cause of the 2003 and 2007 geomagnetic jerks, Geophys. Res. Lett., 37, L07301, doi:10.1029/2009GL042019, 2010.
Ionospheric magnetic field modeling
In a collaboration with the Institut de Physique du Globe de Paris (IPGP) through Swarm's Satellite Constellation Application and Research Facility (SCARF), a project funded by the European Space Agency (ESA), I have been developing new models of quiet-time magnetic field variations originating in the E-layer of the ionosphere. These variations can reach several tens of nT at mid-latitudes (Sq field) and more than 100 nT under the magnetic dip-equator (equatorial electrojet). The Dedicated Ionospheric Field Inversion (DIFI) algorithm makes use of the separation in local time of two of the three Swarm satellites, a unique feature of the Swarm mission compared to previous magnetic satellite missions.
Chulliat, A., P. Vigneron and G. Hulot, First results from the Swarm Dedicated Ionospheric Field Inversion chain, Earth Planets Space, 68:104, doi:10.1186/s40623-016-0481-6, 2016.
Chulliat, A., P. Vigneron, E. Thebault, O. Sirol and G. Hulot, Swarm SCARF Dedicated Ionospheric Field Inversion chain, Earth Planets Space, 65, 1271-1283, doi:10.5047/eps.2013.08.006, 2013.
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