Abstract: The transient variations of the magnetic field at the surface of a planet have a primary external source, the interaction between the environment of the planet and solar radiation, and a secondary source, the electric currents induced in the conductive planet. The continuous recording of the time variations of the magnetic fields at the surface of Mars by means of three-component magnetometers installed on board landers would therefore allow study of both the internal structure of Mars and the dynamic of its ionized environment. The depth of penetration of an electromagnetic wave in a conductive medium depends on both the period of the wave and the electrical resistivity of the medium. The larger the period and the resistivity, the greater the depth of penetration (skin effect). The high frequency spectrum will therefore enable one to estimate the resistivity in the uppermost kilomettes of the planet, and to give information about the presence (or absence) of liquid water under the permafrost. The low frequency spectrum of the transient variations will give information on the presence (or absence) of sharp variations in the resistivity in the uppermost hundreds of kilometres of Mars, and thus on the thermodynamic conditions within the upper mantle of this planet. Averages of the measurements made during “quiet time measurements” would provide a very good estimate of the field of internal origin at the locations of the surface stations. If in addition a total duration of one year or more for the mission can be expected, and a drift on the order of 1 nT per year for the ground-based magnetometer, it might even be possible to detect some dynamo-related secular variation. In addition to the map of the Martian magnetic field which will be produced by the Mars Surveyor 1 orbiter, these ground-based local main field measurements will provide original information on the present and past magnetic field of Mars, and then on its present and past core dynamics. As is the case for the Earth, different possible controlling plasma processes will lead to different convection patterns inside the magnetosphere and therefore different magnetic signatures at the planetary surface. Continuous recordings of the transient variations of the magnetic field on board landers will then provide constraints on the convection within the Martian magnetosphere, that is a small magnetosphere where the ionosphere lies at great heights relative to the dimensions of the magnetospheric cavity.

Abstract: We submit three candidate models following the call for IGRF-11. We apply a simple modeling approach in spherical harmonics based on a quadratic Taylor expansion for the internal field time variations. We use the Dst magnetic index as a proxy for the external field variations. In order to compensate for the limitations incurred by such a conventional approach, we focus on the optimal selection of satellite data in space and time. We also show that some a priori knowledge about the core field state helps us to avoid the pitfall encountered in the case of rapid changes of core field accelerations. Indeed, various acceleration events of relevance for the IGRF 11th occurred between 2003 and 2010, one of them being a geomagnetic jerk. They could entail disagreements between IGRF candidate models for the secular variation (SV) if data prior to 2008 are used. Our SV and main field (MF) candidate models have a root mean square uncertainty less than 6 nT/yr and 8nT, respectively, with respect to the modeled magnetic field contributions. These values correspond to the intrinsic error associated with truncating SV and MF models to spherical harmonic degree 8 and 13, respectively, as requested for IGRF models.

Abstract: published in Data Science Journal (part of the "Proceedings of the XIV
IAGA Workshop on Geomagnetic Observatory Instruments, Data Acquisition,
and Processing")
Abstract:
The K index was devised by Bartels et al. (1939) to provide an
objective monitoring of irregular geomagnetic activity. The K index was
then routinely used to monitor the magnetic activity at permanent
magnetic observatories as well as at temporary stations. The increasing
number of digital and sometimes unmanned observatories and the creation
of INTERMAGNET put the question of computer production of K at the
centre of the debate. Four algorithms were selected during the Vienna
meeting (1991) and endorsed by IAGA for the computer production of K
indices. We used one of them (FMI algorithm) to investigate the impact
of the geomagnetic data sampling interval on computer produced K values
through the comparison of the computer derived K values for the period
2009, January 1st to 2010, May 31st at the Port-aux-Francais magnetic
observatory using magnetic data series with different sampling rates
(the smaller: 1 second; the larger: 1 minute). The impact is
investigated on both 3-hour range values and K indices data series, as
a function of the activity level for low and moderate geomagnetic
activity.