Mid-latitude and equatorial core surface flow variations derived from observatory and satellite magnetic data

Abstract

SUMMARY A series of models of the Earth magnetic field and core surface flow have been simultaneously and sequentially co-estimated from year 1999 to 2022. The models were derived from magnetic satellite and ground observatory data using a linear Kalman filter approach and prior statistics based on numerical dynamo simulations. The core field and secular variation model components present the same characteristics as the most recent core field models with slightly higher resolution in time. A principal component analysis of the core surface flow series of models shows that the largest flow variations are observed at high latitudes and under the western part of the Pacific Ocean. Filtering out the flow variation periods longer than ∼11.5 yr leads to a filtered azimuthal flow that presents ∼7 yr periodicities with patterns propagating westward by ∼60° 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° and 15° latitudes, and flow speed of less than 5 km yr–1. Present at all longitudes, these columnar flows are particularly strong under the Pacific Ocean after 2013. They can also be clearly identified under the Atlantic Ocean from 2005 to 2015.