arXiv subjects

Mioara Mandea

Publications and source records attributed to Mioara Mandea.

4 recordsLinked to original sources

arXiv2026

Ohmic and viscous damping of inner core translational oscillations

Large earthquakes can trigger translational oscillations of Earth's inner core (Slichter modes), yet their damping remains uncertain. Using simulations, we quantify viscous and Ohmic dissipation in the fluid outer core. Earth's rotation splits the motion into one polar and two equatorial modes. We explore all three and derive scaling laws for the quality factor with each dissipation mechanism. Viscous effects are negligible, confined to a thin layer at the inner core boundary. Ohmic dissipation dominates, with decay times of 3-16 years. Equatorial modes damp at least twice as fast as the polar mode. Our results suggest that Slichter modes can persist for years. Their continued non-detection is therefore more likely due to weak excitation than rapid damping.

physics.geo-ph↗

arXiv2020

GRACE -- gravity data for understanding the deep Earth's interior

While the main causes of the temporal gravity variations observed by the GRACE space mission result from water mass redistributions occurring at the surface of the Earth in response to climatic and anthropogenic forcings (e.g., changes in land hydrology, in ocean mass, in mass of glaciers and ice sheets), solid Earth's mass redistributions are also recorded by these observations. This is the case, in particular, for the Glacial Isostatic Adjustment (GIA) or the viscous response of the mantle to the last deglaciation. However, it is only recently showed that the gravity data also contain the signature of flows inside the outer core and their effects on the core-mantle boundary (CMB). Detecting deep Earth's processes in GRACE observations offers an exciting opportunity to provide additional insight on the dynamics of the core-mantle interface. Here, we present one aspect of the GRACEFUL (GRavimetry, mAgnetism and CorE Flow) project, i.e. the possibility to use the gravity field data for understanding the dynamic processes inside the fluid core and core-mantle boundary of the Earth, beside that offered by the geomagnetic field variations.

physics.geo-ph↗

arXiv2010

Regional Modelling of the Southern African Geomagnetic Field using Harmonic Splines

Over the southern African region the geomagnetic field is weak and changes rapidly. For this area series of geomagnetic field measurements exist since the 1950s. We take advantage of the existing repeat station surveys and observatory annual means, and clean these data sets by eliminating jumps and minimising external field contributions in the original time series. This unique data set allows us to obtain a detailed view of the geomagnetic field behaviour in space and time by computing a regional model. For this, we use a system of representation similar to harmonic splines. Initially, the technique is systematically tested on synthetic data. After systematically testing the method on synthetic data, we derive a model for 1961 to 2001 that gives a detailed view of the fast changes of the geomagnetic field in this region.

physics.geo-ph↗

arXiv2007

The SGR 1806-20 magnetar signature on the Earth's magnetic field

SGRs denote ``soft $γ$-ray repeaters'', a small class of slowly spinning neutron stars with strong magnetic fields. On 27 December 2004, a giant flare was detected from magnetar SGR 1806-20. The initial spike was followed by a hard-X-ray tail persisting for 380 s with a modulation period of 7.56 s. This event has received considerable attention, particularly in the astrophysics area. Its relevance to the geophysics community lies in the importance of investigating the effects of such an event on the near-earth electromagnetic environment. However, the signature of a magnetar flare on the geomagnetic field has not previously been investigated. Here, by applying wavelet analysis to the high-resolution magnetic data provided by the CHAMP satellite, a modulated signal with a period of 7.5 s over the duration of the giant flare appears in the observed data. Moreover, this event was detected by the energetic ion counters onboard the DEMETER satellite.

astro-ph↗