Fast equatorial waves propagating at the top of the Earth's core

Since 2000, magnetic field variations originating in the core have been dominated by several pulses in the secular acceleration, leading to sharp geomagnetic jerks at the Earth's surface. Using models built from (i) Defense Meteorological Satellite Program data and (ii) Orsted and Swarm satellites and ground observatory data, we show that a new pulse occurred in 2012.5, immediately following two pulses in 2006 and 2009. The three pulses can be decomposed into several equatorially symmetric modes propagating eastward and westward at 550 to 1100km/yr, and one equatorially antisymmetric mode propagating eastward at 1650km/yr. The characteristics of these modes are compatible to some extent with equatorial magnetic Rossby waves propagating within a 140km thick layer at the top of the core with a density contrast of 50ppm. This interpretation, if confirmed, would provide a new explanation for geomagnetic jerks and pulses based on stable stratification of the core.