Concentric ionospheric currents driven by teleseismic rayleigh waves from the 2011 Tohoku Earthquake

Abstract

Seismo-magnetic disturbances (SMDs) are transient magnetic field anomalies, induced by seismic waves coupled via atmospheric acoustic gravity waves (AGW) to the ionosphere. Using data from 52 geomagnetic stations and 764 seismic stations, with a novel data processing scheme to remove background geomagnetic variations, we provide a detailed view of electric currents associated with a travelling SMD triggered by the 2011 Tohoku earthquake (Mw 9.0). The SMDs lag Rayleigh wave phase arrivals by 6–8 min, corresponding to the time required for acoustic waves to propagate to ionospheric altitudes (110–160 km). The SMDs appear as pulsations at a lower frequency than the driving seismic pulse (4.8 vs. 5.6 mHz), and exhibit a higher Q, with ringing that persists for ∼20 min at some sites. Equivalent ionospheric currents inferred from our array are organized as concentric oscillating circles, centered on the epicenter. These current loops propagate outward with the Rayleigh wave phase velocity (4.08 km/s), but with substantial ringing after passage of the seismic peak. There are coherent large-scale latitude-dependent variations in oscillation frequency and Q, which likely reflect variations in atmospheric conditions, such as temperature, density, and high altitude winds.