BITES

Global validation of data-assimilative electron ring current nowcast for space weather applications

DOI: https://doi.org/10.1038/s41598-024-52187-0 (Haas et al. 2024)

The hazardous plasma environment surrounding Earth poses risks to satellites due to internal charging and surface charging effects. Accurate predictions of these risks are crucial for minimizing damage and preparing for system failures of satellites. To forecast the plasma environment, it is essential to know the current state of the system, as the accuracy of the forecast depends on the accuracy of the initial condition of the forecast. In this study, we use data assimilation techniques to combine observational data and model predictions, and present the first global validation of a data-assimilative electron ring current nowcast during a geomagnetic storm. By assimilating measurements from one satellite and validating the results against another satellite in a different magnetic local time sector, we assess the global response and effectiveness of the data assimilation technique for space weather applications. Using this method, we found that the simulation accuracy can be drastically improved at times when observations are available while eliminating almost all the bias previously present in the model. These findings contribute to the construction of improved operational models in estimating surface charging risks and providing realistic ’source’ populations for radiation belt simulations.

Figure: Schematic representation of the ring current in space: The spheres represent the electrons during the geomagnetic storm, with the colours describing the flux density. Blue means low flux density, red high flux density. The trajectories of the satellites used in this study are also shown. 

The Impact of Grain-Size Distributions of Iron-Oxides on Paleomagnetic Measurements

DOI: https://doi.org/10.1029/2024GC011512 (Out et al. 2024)

Magnetic grains in lavas acquire a magnetic signal while cooling in presence of Earth's magnetic field. However, not all grains preserve the signal well, meaning that both good and bad recorders are present. Classical paleomagnetic techniques measure the magnetic signal of all recorders together, i.e. the bulk signal. New scanning magnetometry techniques such as Micromagnetic Tomography acquire the signal from individual recorders in the lava, enabling the selection of potentially good recorders and the rejection of signals from bad recorders. Here we found that these two types of magnetic measurements do not measure the same grains that are present in the sample: classical techniques emphasize small grains (< 200 nm) while signals in surface magnetometry arise mainly from larger grains with diameter > 1μm. This means that measurements from both techniques performed on the same sample material cannot be compared straightforwardly. Furthermore, our results explain why Micromagnetic Tomography results often are successful, even when many small magnetic grains that intuitively should hamper this technique are present in a sample.

Figure: Overview of the 26.2 × 10.1 × 10.5 μm volume exposed to the slice-and-view procedure with FIB-SEM. 

A global paleosecular variation database for the Paleogene: stationary secular variation behavior since the Triassic?

DOI: https://doi.org/10.1029/2023GC011203 (Engbers et al. 2024)

Paleosecular variation analysis is a primary tool for characterizing ancient geomagnetic behavior and its evolution through time. This study presents a new high-quality directional dataset, paleosecular variation of the Paleogene (PSVP), with and without correction for serial correlation (SC), compiled from 1,667 sites from 45 different localities from the Paleogene and late Cretaceous (84 – 23 Ma). The dataset is used to study the variability, structure, and latitude dependence of the geomagnetic field during that period by varying selection criteria and PSV models. Modeled values for the equatorial virtual geomagnetic pole (VGP) dispersion have over-lapping uncertainty intervals within their uncertainty bounds between 8.3° and 18.6° for the past 250 Ma. We investigate the suitability of two descriptive models of PSV, Model G-style quadratic fits and covariant GGP models, and find that both styles of model fail to satisfactorily reproduce the latitude dependent morphology of PSV, but suggest that estimates of the equatorial VGP dispersion may still robustly characterize aspects of Earth’s long-term field morphology. During this time where the PSV behavior has not changed substantially, the reversal frequency has varied widely. The lack of a clear relationship between PSV behavior and reversal frequency is not trivially explained in the context of published findings regarding numerical geodynamo simulations.

Figure: (left) The Virtual geomagnetic pole (VGP) dispersion versus magnetic latitude for Paleosecular Variation of the Paleogene (PSVP) in colored dots, where the color represents the age (Ma) of the locality, with the VGP dispersion predictions for Model G (red line with light purple shaded area for the bootstrapped 95% confidence bounds), BB-P23 (cyan line), BB-P23SC (blue dashed line), BB18 (purple dashed line, BB-M22 (beige dashed line) and BCE19 (green dashed line).
(right) The Model G parameter a in degrees vs Age. Each green dot with error bounds represents a PSV study with respective Model G parameter a (Cromwell et al., 2018; Doubrovine et al., 2019; Engbers et al., 2022; Handford et al., 2021; de Oliveira et al., 2018). The purple dot with error bounds represents this PSV study from the Paleogene and Late Cretaceous. The areas in blue are the superchrons: CNS = Cretaceous Normal Superchron, PCRS = Permo-Carboniferous Reversed Superchron but also known as the Kiaman Reverse Superchron. In orange the reversal frequency (calculated from Ogg. 2020) is presented for each Myrs, averaged over 5 Myr. The dark green shaded area shows the range of Model G a values (8.3° – 18.6°) with their uncertainty (light green) that the Earth has fluctuated between since the start of the Triassic (250 Ma).

 

Holocene solar activity inferred from global and hemispherical cosmic-ray proxy records

DOI: https://doi.org/10.1038/s41561-024-01467-5 (Nilsson et al. 2024)

Cosmogenic radionuclides, produced in the atmosphere by high energy cosmic rays and measured in well-dated and high-resolution natural archives, can be used to reconstruct variations in solar activity on Holocene timescales and longer. Extracting variations in solar activity from radionuclide data is challenging due to uncertainties in the shielding effect of the geomagnetic field, which is the other main factor controlling the radionuclide production rates. In this study, we show that accounting for differences in hemispherical production rates, related to geomagnetic field asymmetries, helps resolve so far unexplained differences in Holocene solar activity reconstructions. Based on our joint analysis of radionuclide and geomagnetic data, we find no compelling evidence for long-term variations in solar activity and show that variations in cosmogenic radionuclide production rates on millennial timescales and longer, including the 2,400-year Hallstatt cycle, are explained by variations in the geomagnetic field. Our results also suggest an on-average stronger dipole moment during the Holocene, associated with higher field intensities in the Southern Hemisphere.

 

Figure: Model predictions of variations in (a) geomagnetic dipole moment, (b) large-scale field asymmetry and (c) solar activity over the past 9000 years. Shaded areas represent 95% uncertainty ranges.