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Geomagnetic observations from satellites have highlighted interannual variations in the rate of change of the magnetic field originating from Earth’s core. Downward continued to the core surface, these variations primarily show up in the equatorial belt. First, we recall the main characteristics of these patterns, addressing their spatio-temporal resolution, as seen from field models. We then review the several dynamical frameworks proposed so far to understand and model these observations, which populate the frequency spectrum on time scales close to the Alfvén time τA≈2 yr, much shorter than the vortex turnover time τU≈150 yr in Earth’s core. Magnetic–Archimedes–Coriolis (MAC) waves in a stratified layer below the core surface constitute a first possibility in the case of a sub-adiabatic heat flux at the top of the core. Their period may reach the interannual range for a layer thickness less than ≈30 km, for a buoyancy frequency of the order of the Earth’s rotation rate. An alternative has been proposed in a context where the Coriolis force dominates the momentum balance, rendering transient motions almost invariant along the rotation axis (quasi-geostrophy, QG). Torsional Alfvén waves, consisting of axisymmetric QG motions, operate at periods similar to the Alfvén time, but are not sufficient to explain the interannual field changes, which require non-axisymmetric motions. QG Alfvén waves (involving the Coriolis and magnetic forces) constitute another possibility, with inertia playing an important role. They have been detected in the latest generation of geodynamo simulations, propagating in a ubiquitous manner at a speed slightly less than the Alfvén velocity. They are localized in longitude and as a result their description requires high azimuthal wavenumber. But the branch of QG waves with large extent in azimuth is also worth considering, as it reaches interannual periods as their radial wavenumber is increased. The excitation of such high-frequency dynamics is discussed with respect to the temporal spectrum of the core field, which presents a slope ∼f-4 for periods approximately between τA and τU. We finally summarize the main geophysical implications of the existence of this interannual dynamics on core and lower mantle structure, properties, and dynamics.

In December 2019, the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group (V-MOD) adopted the thirteenth generation of the International Geomagnetic Reference Field (IGRF). This IGRF updates the previous generation with a definitive main field model for epoch 2015.0, a main field model for epoch 2020.0, and a predictive linear secular variation for 2020.0 to 2025.0. This letter provides the equations defining the IGRF, the spherical harmonic coefficients for this thirteenth generation model, maps of magnetic declination, inclination and total field intensity for the epoch 2020.0, and maps of their predicted rate of change for the 2020.0 to 2025.0 time period.

We present CHAOS-8, an extension of the CHAOS field model series that describes the time-dependent near-Earth geomagnetic field, valid from 1999 to 2025. It is estimated from magnetic measurements collected by multiple low-earth-orbit satellites, such as CHAMP and Swarm , and ground observatories. An initial version of this model, CHAOS-8.1, served as the parent model for constructing DTU’s candidate models for the 14th generation International Geomagnetic Reference Field. CHAOS-8 comprises a time-dependent internal field up to spherical harmonic degree 20, a static internal field that merges with the LCS-1 lithospheric field model above degree 25, a model of the magnetospheric field and its induced counterpart, and estimates of alignment parameters for satellite vector magnetometers, along with calibration parameters for platform magnetometers. It also includes a co-estimated climatological model of the ionospheric field previously ignored within the CHAOS framework. The climatological model describes magnetic fields produced by polar ionospheric E-layer currents, which can be significant even under dark conditions. A new temporal regularization of the internal field is implemented, based on a priori statistics of the secular acceleration extracted from numerical geodynamo simulations. This enables rapid internal field changes to be better captured at small length scales. Magnetic measurements from the MSS-1 and CSES satellite missions were included for the first time in a CHAOS model. Model parameters were estimated using regularized iteratively reweighted least squares. The fit to the data was generally comparable to earlier versions of the CHAOS model. Co-estimation of an ionospheric field resulted in an improved fit in the polar regions. The new temporal regularization allowed stronger and more rapid temporal variations of the internal field at high spherical harmonic degrees. Analyzing sub-decadal variations of the internal field at the core–mantle boundary, we find westward-moving features and tentative evidence for eastward-moving features at low latitudes. The latter are of small length scales (apparent azimuthal wavenumber 13), moving at a speed of 200km/yr at the equator between 0 ∘ and 90 ∘ E after 2012. There are also indications of features moving across the geographic equator. These propagating features provide further evidence of traveling hydromagnetic waves at the core–mantle boundary. Graphical Abstract

Evidence of fast variations in the Earth’s core field are seen both in magnetic observatory and satellite records. We present here how they have been identified at the Earth’s surface from ground-based observatory records and how their spatio-temporal structure is now characterised by satellite data. It is shown how their properties at the core mantle boundary are extracted through localised and global modelling processes, paying particular attention to their time scales. Finally are listed possible types of waves in the liquid outer core, together with their main properties, that may give rise to these observed fast variations.

In December 2019, the 13th revision of the International Geomagnetic Reference Field (IGRF) was released by the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group V-MOD. This revision comprises two new spherical harmonic main field models for epochs 2015.0 (DGRF-2015) and 2020.0 (IGRF-2020) and a model of the predicted secular variation for the interval 2020.0 to 2025.0 (SV-2020-2025). The models were produced from candidates submitted by fifteen international teams. These teams were led by the British Geological Survey (UK), China Earthquake Administration (China), Universidad Complutense de Madrid (Spain), University of Colorado Boulder (USA), Technical University of Denmark (Denmark), GFZ German Research Centre for Geosciences (Germany), Institut de physique du globe de Paris (France), Institut des Sciences de la Terre (France), Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (Russia), Kyoto University (Japan), University of Leeds (UK), Max Planck Institute for Solar System Research (Germany), NASA Goddard Space Flight Center (USA), University of Potsdam (Germany), and Université de Strasbourg (France). The candidate models were evaluated individually and compared to all other candidates as well to the mean, median and a robust Huber-weighted model of all candidates. These analyses were used to identify, for example, the variation between the Gauss coefficients or the geographical regions where the candidate models strongly differed. The majority of candidates were sufficiently close that the differences can be explained primarily by individual modeling methodologies and data selection strategies. None of the candidates were so different as to warrant their exclusion from the final IGRF-13. The IAGA V-MOD task force thus voted for two approaches: the median of the Gauss coefficients of the candidates for the DGRF-2015 and IGRF-2020 models and the robust Huber-weighted model for the predictive SV-2020-2025. In this paper, we document the evaluation of the candidate models and provide details of the approach used to derive the final IGRF-13 products. We also perform a retrospective analysis of the IGRF-12 SV candidates over their performance period (2015–2020). Our findings suggest that forecasting secular variation can benefit from combining physics-based core modeling with satellite observations.

Rapidly rotating convection in spherical geometry outside the tangent cylinder is investigated using the quasi-geostrophic approximation. The validity of the approximation is discussed, and numerical simulations using these equations are performed, reaching Ekman numbers, $E$, down to $10^{-6}$. The results are compared with experiments and fully three-dimensional numerical simulations. We find that the inertial scaling developed to study rapidly rotating convection does not represent the Prandtl-number dependence of our results adequately. Instead, we find that even in strongly supercritical situations the dominant wavenumbers at the onset of convection still have a strong influence on the behaviour. We find that the local Péclet number, the product of the typical convective velocity and local convective length scale divided by the thermal diffusivity, is helpful for understanding the dynamics of rapidly rotating convection. We explore the zonal flows driven by Reynolds stresses with no-slip boundaries and explore their Prandtl-number dependence. We also study the convective heat transport at low $E$, and consider the boundary layer structures that can form at large Rayleigh number, slowing down the rate of growth of the Nusselt number with Rayleigh number.

Although authentic leadership is known to improve caregivers' functioning, health, and quality of care, information is lacking about whether the authentic leadership subdimensions may be distinguished from an overarching authentic leadership global construct, and how these global and specific factors can combine within various profiles to explain outcomes over time. Relying on an integration of person- and variable-centered perspectives, this study aims to provide a deeper understanding of the dimensionality of the authentic leadership construct. Specifically, it aims to examine the profiles taken by authentic leadership dimensions, document their stability over time, and explore the associations between these profiles and outcomes (need satisfaction, anhedonia, and safety of care). A questionnaire was completed twice over a one-year period by 750 healthcare professionals. Latent transition analysis was the primary method of analysis. Our results showed that employees' perceptions of authentic leadership behaviors reflected an overarching construct simultaneously coexisting with four specific dimensions (self-awareness, internalized moral perspective, relational transparency, and balanced processing). We identified four profiles highly stable over time: , and . Finally, employees' global and specific (relatedness, competence, and autonomy) levels of need satisfaction as well as perceptions of safety of care and anhedonia differed as a function of their profile, with the most positive outcomes associated with the profile. In addition to confirming that authentic leadership may be studied as a global construct, this study highlights the importance of considering the combinations of global and specific factors in explaining variations in caregivers' need satisfaction, anhedonia, and quality of care over a one year-period. Our findings suggest that managers should strive to implement a complete array of authentic leadership behaviors at a balanced level to ensure positive outcomes.

Projections from auditory cortex to the amygdala are thought to contribute to the induction of auditory fear learning. In addition, fear conditioning has been found to enhance cortical responses to conditioned tones, suggesting that cortical plasticity contributes to fear learning. However, the functional role of auditory cortex in the retrieval of fear memories is unclear and how fear learning regulates cortical sensory representations is not well understood. To address these questions, we use acute optogenetic silencing and chronic two-photon calcium imaging in mouse auditory cortex during fear learning. Longitudinal imaging of neuronal ensemble activity reveals that discriminative fear learning modulates cortical sensory representations via the suppression of cortical habituation.

RésuméCette étude a pour objectif d’identifier les profils motivationnels des salariés d’une entreprise privée puis d’analyser comment ces individus se différencient sur des variables d’ajustement organisationnel telles que le stress perçu, la performance au travail et l’implication organisationnelle. Une analyse en cluster a permis de mettre en évidence trois profils motivationnels reflétant différents niveaux de motivation autodéterminée et de motivation contrôlée, différemment reliés aux variables organisationnelles. Le profil motivationnel le plus autodéterminé (caractérisé par des niveaux élevés de motivation autodéterminée, des niveaux modérés de motivation contrôlée et des niveaux faibles d’amotivation) est associé à des conséquences généralement plus positives que les deux autres profils motivationnels (moins autodéterminés). Ces résultats sont en accord avec les postulats de la théorie de l’autodétermination (Deci et Ryan, 1985) et suggèrent que l’analyse en cluster est une technique particulièrement intéressante pour étudier et mieux comprendre la motivation des salariés envers leur activité professionnelle. SummaryThis research aims to identify individuals’ motivational profiles in a private organization and investigate whether these workers differ on some work outcomes, such as perceived stress, performance and organizational commitment. A cluster analysis showed three motivational profiles which were linked in different ways to the organizational variables studied. The most self-determined motivational profile was characterized by high levels of autonomous motivation, moderate levels of controlled motivation and low-levels of amotivation. This profile was generally associated with more positive consequences than the other two profiles. Overall, these findings are in accordance with the tenets of self-determination theory (Deci and Ryan, 1985). They suggest that cluster analysis is useful for studying and understanding workers’ motivation.