Periodic Reporting for period 3 - CoreSat (Dynamics of Earth’s core from multi-satellite observations)
Período documentado: 2021-03-01 hasta 2022-08-31
Earth’s magnetic field plays a fundamental role in our planetary habitat, controlling interactions between the Earth and the solar wind. Yet observations show a region of persistently weak field in the South Atlantic that has grown in size in recent decades. Pinning down the core dynamics responsible for this behaviour is essential if we are to understand the present geodynamo, and to forecast future magnetic field changes. Global magnetic observations from the Swarm satellite constellation mission, with three identical satellites now carrying out the most detailed ever survey of the geomagnetic field, today provide us with the means to probe the responsible core dynamics in exquisite detail and test hypotheses concerning the origin of field changes in the South Atlantic.
The objectives of the CoreSat project are to use multi-satellite magnetic field measurements to
1. Reveal small scales and rapid time changes of the core-generated magnetic field
2. Test whether rotation-dominated core convection can explain the recent time-dependence of the South Atlantic Anomaly.
The objectives of the CoreSat project are to use multi-satellite magnetic field measurements to
1. Reveal small scales and rapid time changes of the core-generated magnetic field
2. Test whether rotation-dominated core convection can explain the recent time-dependence of the South Atlantic Anomaly.
Regarding objective 1.
Work performed so far:
New software for deriving improved global models of the core-generated geomagnetic field has been developed. This allows simultaneous estimation of parameters describing the core field, magnetospheric and related induced fields, fields due to polar ionospheric currents, and platform magnetometer calibration parameters. New models of the core-generated magnetic field have been derived using the latest data from the three Swarm satellites, the CHAMP, Oersted, SAC-C, satellites, ground observatory data and also platform magnetometer data from the CryoSat-2 mission. Analysis of recent changes in the South Atlantic Anomaly, and in the north magnetic pole position, in terms of changes in the core-mantle boundary field has been carried out. A new probabilistic methodology for coestimating the core and lithospheric fields based on prior information from geology information and numerical dynamo simulations has been developed. New instrumentation in the magnetic observatories in Greenland, in particular the absolute scalar magnetometers, have been installed and are now in service.
Main results:
The derived models of the core-generated field have revealed the development of a smaller-scale secondary minimum in the magnetic field intensity that has developed South-west of Africa at Earth’s surface over the past six years. It has also been possible to use these models to clarify the reason for recent rapid motions of the north magnetic pole, due to the diminishing of the concentration of magnetic flux on the core-mantle boundary beneath North America.
Regarding objective 2.
Work performed so far:
An existing numerical code for modelling rapidly-rotating core convection has been extended to consider the temperature field and a resulting thermal wind in 3D, and to allow for the possibility for inhomogeneous heat flux boundary conditions, as appropriate for Earth's core-mantle boundary. This hybrid core convection code has also been coupled to a 3D solver of the magnetic induction equation, allowing the impact of strongly-driven, rotation-dominated convection on the magnetic field to be assessed. A systematic study of core convection, in the strongly-driven, rapidly-rotating, regime, has been carried out as a function of control parameters and scaling laws for eddy size and the dynamical balance have been tested. A new high performance computing cluster suitable for running the hybrid 2D-3D core convection code has been established.
Main results:
The hybrid 2D-3D core convection model reproduces well the structure of convection from fully 3D simulations in the bulk of the spherical shell, including the structure of the thermal wind. Systematic study shows the eddy size depends on the ratio of the thermal to viscous diffusivities but is nonetheless well described by the Rhines scale (derived from the ratio flow speed and the gradient of planetary vorticity), and that the flow closely obeys a Coriolis-Inertial-Archimedes balance. Inhomogeneous heat flux boundary conditions are found to impact the convection, inhibiting the convection below regions of low heat flux on the core-mantle boundary, even for highly supercritical convection in the rapidly-rotating regime.
Work performed so far:
New software for deriving improved global models of the core-generated geomagnetic field has been developed. This allows simultaneous estimation of parameters describing the core field, magnetospheric and related induced fields, fields due to polar ionospheric currents, and platform magnetometer calibration parameters. New models of the core-generated magnetic field have been derived using the latest data from the three Swarm satellites, the CHAMP, Oersted, SAC-C, satellites, ground observatory data and also platform magnetometer data from the CryoSat-2 mission. Analysis of recent changes in the South Atlantic Anomaly, and in the north magnetic pole position, in terms of changes in the core-mantle boundary field has been carried out. A new probabilistic methodology for coestimating the core and lithospheric fields based on prior information from geology information and numerical dynamo simulations has been developed. New instrumentation in the magnetic observatories in Greenland, in particular the absolute scalar magnetometers, have been installed and are now in service.
Main results:
The derived models of the core-generated field have revealed the development of a smaller-scale secondary minimum in the magnetic field intensity that has developed South-west of Africa at Earth’s surface over the past six years. It has also been possible to use these models to clarify the reason for recent rapid motions of the north magnetic pole, due to the diminishing of the concentration of magnetic flux on the core-mantle boundary beneath North America.
Regarding objective 2.
Work performed so far:
An existing numerical code for modelling rapidly-rotating core convection has been extended to consider the temperature field and a resulting thermal wind in 3D, and to allow for the possibility for inhomogeneous heat flux boundary conditions, as appropriate for Earth's core-mantle boundary. This hybrid core convection code has also been coupled to a 3D solver of the magnetic induction equation, allowing the impact of strongly-driven, rotation-dominated convection on the magnetic field to be assessed. A systematic study of core convection, in the strongly-driven, rapidly-rotating, regime, has been carried out as a function of control parameters and scaling laws for eddy size and the dynamical balance have been tested. A new high performance computing cluster suitable for running the hybrid 2D-3D core convection code has been established.
Main results:
The hybrid 2D-3D core convection model reproduces well the structure of convection from fully 3D simulations in the bulk of the spherical shell, including the structure of the thermal wind. Systematic study shows the eddy size depends on the ratio of the thermal to viscous diffusivities but is nonetheless well described by the Rhines scale (derived from the ratio flow speed and the gradient of planetary vorticity), and that the flow closely obeys a Coriolis-Inertial-Archimedes balance. Inhomogeneous heat flux boundary conditions are found to impact the convection, inhibiting the convection below regions of low heat flux on the core-mantle boundary, even for highly supercritical convection in the rapidly-rotating regime.
Progress beyond state of the art so far:
On the observational side, we have developed the first geomagnetic field modelling scheme capable of coestimating the core-generated magnetic field and the fields due to polar current systems, where the later depend explicitly on solar wind driving parameters. In parallel we have developed a novel method for probabilistically modelling core and lithospheric fields based on prior knowledge from geology and numerical dynamos. On the theoretical side, a hybrid 2D-3D core convection code has been developed in a spherical shell geometry, with the possibility of imposing inhomogeneous heat flux boundary conditions and with a coupling to a 3D magnetic induction solver. This enables an efficient exploration of parameter space in the regime of strongly-driven, rapidly-rotating, convection in a spherical shell geometry appropriate for Earth’s outer core.
Expected results until end of the project:
On the observational side, we will clarify the impact of co-estimated polar current systems on the core-generated field, and explore relaxing the conventional temporal smoothing to study rapid time changes of the core field. Probabilistic models of the internal field, treating the core field and the lithospheric field as separate models will be derived from Swarm and CHAMP satellite data. On the theoretical side, we will study the patterns of secular variation generated by our hybrid 2D-3D core convection model when coupled to a 3D magnetic field. A data assimilation scheme will be implemented in an effort to assess whether such quasi-geostrophic core convection can account for the recent evolution of the South Atlantic weak field anomaly.
On the observational side, we have developed the first geomagnetic field modelling scheme capable of coestimating the core-generated magnetic field and the fields due to polar current systems, where the later depend explicitly on solar wind driving parameters. In parallel we have developed a novel method for probabilistically modelling core and lithospheric fields based on prior knowledge from geology and numerical dynamos. On the theoretical side, a hybrid 2D-3D core convection code has been developed in a spherical shell geometry, with the possibility of imposing inhomogeneous heat flux boundary conditions and with a coupling to a 3D magnetic induction solver. This enables an efficient exploration of parameter space in the regime of strongly-driven, rapidly-rotating, convection in a spherical shell geometry appropriate for Earth’s outer core.
Expected results until end of the project:
On the observational side, we will clarify the impact of co-estimated polar current systems on the core-generated field, and explore relaxing the conventional temporal smoothing to study rapid time changes of the core field. Probabilistic models of the internal field, treating the core field and the lithospheric field as separate models will be derived from Swarm and CHAMP satellite data. On the theoretical side, we will study the patterns of secular variation generated by our hybrid 2D-3D core convection model when coupled to a 3D magnetic field. A data assimilation scheme will be implemented in an effort to assess whether such quasi-geostrophic core convection can account for the recent evolution of the South Atlantic weak field anomaly.