ALBERT

Description: The last version of the World Digital Magnetic Anomaly Map (WDMAM v. 2.0) was released in 2015 (Dyment et al., EPSL, 2015; Lesur et al., EPS, 2016) with the mandate to update it using the same methodology when new data become available. The new version 2.1, compiled at 5 km interval, at 5 km altitude above the continents and at sea-level over the oceans, includes new datasets: (1) the complete digital aeromagnetic map of Brasil made available by ANP; (2) an improved version of the aeromagnetic map of Russia prepared by V-SEGEI; (3) the second version of the Antarctic Digital Magnetic Anomaly maP (ADMAP; Golynsky et al., GRL, 2018) which results from a remarkable international effort during and after the Second International Polar Year; (4) a new map of the Caribbean Plate and Gulf of Mexico (Garcia and Dyment, EPSL, 2021, 2022); (5) the updated Magnetic Anomaly Map of Eastern Asia prepared by the CCOP (MAMEA; Ishihara and Uchida, 2021); and (6) a new marine magnetic anomaly data compilation prepared by T. Ishihara and coworkers. The remaining data gaps are filled with a satellite anomaly model (Thebault et al., GRL, 2021). Long wavelengths of degree and order lower than 120 are filtered and replaced by those computed between order and degree 16 and 120 using the same satellite magnetic anomaly model from CHAMP and Swarm data. The new map will be presented and its significant improvements over the previous version discussed.

Description: A large collection of photographic paper magnetograms, covering globally an entire century is preserved in the archives of Chambon-la-forêt magnetic observatory, France. It contains magnetograms from various instruments and observatories: the National magnetic observatory (it moved from Parc-Saint-Maur, to Val-Joyeux, to Chambon-la-forêt), Bangui (Central African Republic), M’bour (Senegal), Pamatai (French Polynesia), and other observatories in metropolitan France at the beginning of the 20th century. Only values from tables of hand-written hourly values from the National magnetic observatory and overseas observatories had been digitised and made available to the scientific community. In order to access additional information on the magnetic variations recorded on the magnetograms, we developed a recovering software: RECOV. It is based on MATLAB and can be run either as a MATLAB App, or as a standalone desktop application, with MATLAB Runtime. It provides an interface for manual selection of magnetic traces that are converted into magnetic variations and calibrated time series, if definitive hourly time series are available. The user can recover magnetograms of different quality, even cases when the magnetic traces cross the temporal axis, or wrap-around traces appear during the strongest storms. We aim obtaining recovered time-series with sampling every minute, with a reliability depending on the size and resolution of magnetic traces. We present results of recovered magnetic variations during magnetic storms of 1958 and comparisons between different instruments.

Description: The magnetic observatory network of the “Institut de physique du globe de Paris” (IPGP) includes the French national magnetic observatory, and a series of 11 other observatories in the world, managed in collaboration with local institutions, in Algeria, Senegal, Cameroon, French Guyana, Easter Island, French Polynesia, Vietnam, China, La Réunion Island and Russia. This network includes also two variometer stations set in France. The status of the observatories composing this network will be presented. Three observatories are new and not yet part of the INTERMAGNET network: the EDA observatory near Edéa in Cameroon, the SOK observatory near Niakhar in Senegal, and the REU observatory on La Réunion Island, set in 2018, 2020 and 2022, respectively. The variometer stations have been set close to Clermont-Ferrand in central France, in 2021 and near Brest in Brittany, in 2023. They deliver vector and scalar measurements in quasi real-time. The data from these observatories and stations are already freely available on the “Bureau Central de Magnétisme Terrestre” (BCMT) website, along with data from other French observatories: http://www.bcmt.fr

Description: A series of models of the Earth magnetic field and core surface flow are presented. The models were derived sequentially from year 1999 to 2022, using magnetic satellite and ground observatory data. A linear Kalman filter approach and prior statistics based on numerical dynamo runs were used. The core field and secular variation models present the same characteristics as the most recent core field models with slightly higher resolution in time. The core surface flow series of models presents large variations at high latitudes and under the western part of the Pacific Ocean. Filtering out the flow variation periods longer than 11.5 years leads to a filtered azimuthal flow with ∼7 years periodicities and patterns propagating westward by ∼60º longitude per year. These patterns are present mainly at mid- and equatorial latitudes. They are compatible with a perturbation of the main flow made of small columnar flows with rotation axis intersecting the core-mantle boundary between 10º to 15º latitudes, and flow speed of less than 5km/y. These columnar flows can be identified at all longitudes, but are particularly strong under the Pacific Ocean or under the Atlantic Ocean from 2005 to 2015.