Atmosphere-Ionosphere Response to the M9 Tohoku Earthquake Revealed by Joined Satellite and Ground Observations. Preliminary results

The recent M9 Tohoku Japan earthquake of March 11, 2011 was the largest recorded earthquake ever to hit this nation. We retrospectively analyzed the temporal and spatial variations of four different physical parameters - outgoing long wave radiation (OLR), GPS/TEC, Low-Earth orbit tomography and critical frequency foF2. These changes characterize the state of the atmosphere and ionosphere several days before the onset of this earthquake. Our first results show that on March 8th a rapid increase of emitted infrared radiation was observed from the satellite data and an anomaly developed near the epicenter. The GPS/TEC data indicate an increase and variation in electron density reaching a maximum value on March 8. Starting on this day in the lower ionospheric there was also confirmed an abnormal TEC variation over the epicenter. From March 3-11 a large increase in electron concentration was recorded at all four Japanese ground based ionosondes, which return to normal after the main earthquake. We found a positive correlation between the atmospheric and ionospheric anomalies and the Tohoku earthquake. This study may lead to a better understanding of the response of the atmosphere /ionosphere to the Great Tohoku earthquake

💡 Research Summary

The paper investigates atmospheric and ionospheric anomalies associated with the March 11, 2011 Mw 9.0 Tohoku earthquake by integrating four independent observational techniques: outgoing long‑wave radiation (OLR) from NOAA‑AVHRR, Global Ionosphere Maps (GIM) of total electron content (TEC) derived from GPS, low‑Earth‑orbit (LEO) satellite ionospheric tomography, and ground‑based ionosonde measurements of the critical frequency foF2 at four Japanese stations.

Using a long‑term (2004‑2011) climatology, the authors defined a statistical anomaly index (E‑index) for OLR. On 8 March, three days before the main shock, an OLR spike exceeding +2 σ appeared directly above the future epicenter, suggesting enhanced latent heat release possibly linked to radon‑induced ionization and condensation processes.

GPS‑TEC analysis employed differential maps (current minus 15‑day mean), Global Electron Content (GEC) calculations, and a localized GEC integration within a 30° radius of the epicenter. All metrics displayed a pronounced peak on 8 March, while global solar activity (F10.7) and two minor geomagnetic storms (1 March and 13 March) could not account for the localized nature of the signal.

LEO tomography, based on phase‑difference measurements of COSMOS, OSCAR‑31, and RADCAL satellite signals received at Sakhalin, revealed a slant‑TEC enhancement of ~1.5 TECU at ~45° N latitude on 8 March 19:29 UTC. The reconstructed electron‑density structure extended 100‑150 km along the latitude and was ~50 % denser than the background.

Ground ionosonde data showed a general increase in foF2 from early March, largely attributable to rising solar flux, but a cross‑correlation analysis between the nearest station (Kokubunji) and a more distant one (Yamagawa) uncovered a sharp drop in correlation on 8 March, indicating a local ionospheric disturbance. All four stations recorded a peak in electron concentration on that day, returning to baseline after the main event.

The authors interpret these coincident anomalies as evidence of Lithosphere‑Atmosphere‑Ionosphere Coupling (LAIC). They propose that stress‑induced radon emission from the crust ionizes near‑surface air, leading to latent heat release, increased atmospheric conductivity, and upward propagation of electric fields, which in turn modify ionospheric electron density and foF2. The timing (8 March) aligns across all datasets, despite the presence of two minor geomagnetic storms and a rapid increase in solar F10.7, reinforcing the hypothesis that the observed signals are earthquake‑related rather than solar or geomagnetic artifacts.

In summary, the study provides a multi‑parameter, multi‑platform case study demonstrating that atmospheric infrared emission, GPS‑TEC, ionospheric tomography, and foF2 can all exhibit pre‑seismic anomalies localized near the epicenter. These findings support the feasibility of using coupled atmosphere‑ionosphere observations as part of an early‑warning framework for large megathrust earthquakes.