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International audience; The geomagnetic field has been continuously monitored from low-Earth orbit (LEO) since 1999, complementing ground-based observatory data by providing calibrated scalar and vector measurements with global coverage. The successful three-satellite ESA Swarm constellation is expected to remain in operation up to at least 2025. Further monitoring the field from space with high-precision absolute magnetometry beyond that date is of critical importance for improving our understanding of dynamics of the multiple components of this field, in particular that of the core field, as well as the ionospheric environment. Here, we will report on the latest status of the NanoMagSat project, which aims to deploy and operate a new constellation concept of three identical 16U nanosatellites, using two inclined (approximately 60°) and one polar LEO, as well as an innovative payload including an advanced Miniaturized Absolute scalar and self-calibrated vector Magnetometer (MAM) combined with a set of precise star trackers (STR), a compact High-frequency Field Magnetometer (HFM, sharing subsystems with the MAM), a multi-needle Langmuir Probe (m-NLP) and dual frequency GNSS receivers. The data to be produced will at least include 1 Hz absolutely calibrated and oriented magnetic vector field (using the MAM and STR), 2 kHz very low noise magnetic scalar (using the MAM) and vector (using the HFM) field, 2 kHz local electron density and 1 Hz electron temperature (using the m-NLP) as well as precise timing, location and TEC products. The three-satellite constellation design is such that all local times at all geographic locations between 60°N and 60°S will be covered in a little more than one month, much faster than Swarm, which the NanoMagSat is also designed to complement for even better coverage, should Swarm still be in operation at the time of launch. In addition to presenting the nanosatellite and mission concepts, as well as the latest status of the mission (which started in January 2022 an 18 months phase of risk retirements activities funded by ESA), this presentation will focus on the expected ability of NanoMagSat to recover fast core field signals at mid and low latitudes that no previous mission could document so far, but which numerical simulations of the dynamo strongly suggest are very likely produced within the Earth's core.

We analyse models describing time changes of the Earth’s core magnetic field (secular variation) covering the historical period (several centuries) and the more recent satellite era (previous decade), and we illustrate how both the information contained in the data and the a priori information (regularisation) affect the result of the ill-posed geomagnetic inverse problem. We show how data quality, frequency and selection procedures govern part of the temporal changes in the secular variation norms and spectra, which are sometimes difficult to dissociate from true changes of the core state. We highlight the difficulty of resolving the time variability of the high degree secular variation coefficients (i.e. the secular acceleration), arising for instance from the challenge to properly separate sources of internal and of external origin. In addition, the regularisation process may also result in artificial changes in the model norms and spectra. Model users should keep in mind that such features can be miss-interpreted as the signature of physical mechanisms (e.g. diffusion). Finally, we present perspectives concerning core field modelling: imposing dynamical constraints (e.g. by means of data assimilation) reduces the non-uniqueness of the geomagnetic inverse problem. The article is also available electronically on SpringerLink: http://www.springerlink.com/openurl.asp?genre=article&id= doi:1.0.1007/s11214-009-9586-6

Swarm a three satellite constellation to study the dynamics of the Earth's magnetic field and its interactions with the Earth system is expected to be launched in late 2013. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution in order to gain new insights into the Earth system by improving our understanding of the Earth's interior and environment. In order to derive advanced models of the geomagnetic field (and other higher level data products) it is necessary to take explicit advantage of the constellation aspect of Swarm. The Swarm SCARF (Satellite Constellation Application and Research Facility) has been established with the goal of deriving Level 2 products by combination of data from the three satellites and of the various instruments. The present paper describes the Swarm input data products (Level lb and auxiliary data) used by SCARF the various processing chains of SCARF and the Level 2 output data products determined by SCARF. Copyright © The Society of Geomagnelism and Earth Planetary and Space Sciences (SGEPSS).

The secular variation of the core field is generally characterized by smooth variations, sometimes interrupted by abrupt changes, named geomagnetic jerks. The origin of these events, observed and investigated for over three decades, is still not fully understood. Many fundamental features of geomagnetic jerks have been the subject of debate, including their origin internal or external to the Earth, their occurrence dates, their duration and their global or regional character. Specific tools have been developed to detect them in geomagnetic field or secular variation time series. Recently, their investigation has been advanced by the availability of a decade of high-quality satellite measurements. Moreover, advances in the modelling of the core field and its variations have brought new perspectives on the fluid motion at the top of the core, and opened new avenues in our search for the origin of geomagnetic jerks. Correlations have been proposed between geomagnetic jerks and some other geophysical observables, indicating the substantial interest in this topic in our scientific community. This paper summarizes the recent advances in our understanding and interpretation of geomagnetic jerks.

International audience; Using observatory data, we report the detection of a geomagnetic jerk in 2007, which we relate to a jump in the second derivative of the geomagnetic field previously noted in satellite data. Although not of worldwide extent, this jerk is very intense in the South Atlantic region. Using the CHAOS-2 model, we show that both this jerk and the previous 2003 jerk are caused by a single core field acceleration pulse reaching its maximum power near 2006.0. This pulse seems to be simultaneously occurring in several regions of the core surface where it corresponds to dominant n = 5 and 6 spherical harmonic modes. Geometrical attenuation explains why the 2003 and 2007 jerks are local and not fully synchronized at the Earth's surface. Our results suggest that this core field acceleration pulse is the relevant phenomenon to be investigated from the point of view of core dynamics, rather than the jerks themselves.