Core surface flow variations derived from observatory and satellite magnetic data

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 ∼60^o 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 10^o to 15^o 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.