No abstract

We demonstrate extreme ionospheric response to the large interplanetary electric fields during the “Halloween” storms that occurred on October 29 and 30, 2003. Within a few (2–5) hours of the time when the enhanced interplanetary electric field impinged on the magnetopause, dayside total electron content increases of ∼40% and ∼250% are observed for the October 29 and 30 events, respectively. During the Oct 30 event, ∼900% increases in electron content above the CHAMP satellite (∼400 km altitude) were observed at mid‐latitudes (±30 degrees geomagnetic). The geomagnetic storm‐time phenomenon of prompt penetration electric fields is a possible contributing cause of these electron content increases, producing dayside ionospheric uplift combined with equatorial plasma diffusion along magnetic field lines to higher latitudes, creating a “daytime super‐fountain” effect.

The 15 January 2022 climactic eruption of Hunga volcano, Tonga, produced an explosion in the atmosphere of a size that has not been documented in the modern geophysical record. The event generated a broad range of atmospheric waves observed globally by various ground-based and spaceborne instrumentation networks. Most prominent is the surface-guided Lamb wave ( ≲ 0.01 Hz), which we observed propagating for four (+three antipodal) passages around the Earth over six days. Based on Lamb wave amplitudes, the climactic Hunga explosion was comparable in size to that of the 1883 Krakatau eruption. The Hunga eruption produced remarkable globally-detected infrasound (0.01–20 Hz), long-range (~10,000 km) audible sound, and ionospheric perturbations. Seismometers worldwide recorded pure seismic and air-to-ground coupled waves. Air-to-sea coupling likely contributed to fast-arriving tsunamis. We highlight exceptional observations of the atmospheric waves.

[1] We observe ionospheric perturbations caused by the Tohoku earthquake and tsunami of March 11, 2011. Perturbations near the epicenter were found in measurements of ionospheric total electron content (TEC) from 1198 GPS receivers in the Japanese GEONET network. For the first time for this event, we compare these observations with the estimated magnitude and speed of a tsunami-driven atmospheric gravity wave, using an atmosphere-ionosphere-coupling model and a tsunami model of sea-surface height, respectively. Traveling ionospheric disturbances (TIDs) were observed moving away from the epicenter at approximate speeds of 3400 m/s, 1000 m/s and 200-300 m/s, consistent with Rayleigh waves, acoustic waves, and gravity waves, respectively. We focus our analysis on gravity waves moving south and east of the epicenter, since tsunamis propagating in the deep ocean have been shown to produce gravity waves detectable in ionospheric TEC in the past. Observed southeastward gravity wave perturbations, seen $60 min after the earthquake, are mostly between 0.5 to 1.5 TECU, representing up to $5% of the background vertical TEC (VTEC). Comparisons of observed TID gravity waves with the modeled tsunami speed in the ocean and the predicted VTEC perturbation amplitudes from an atmosphere-ionosphere-coupling model show the measurements and models to be in close agreement. Due to the dense GPS network and high earthquake magnitude, these are the clearest observations to date of the effect of a major earthquake and tsunami on the ionosphere near the epicenter. Such observations from a future realtime GPS receiver network could be used to validate tsunami models, confirm the existence of a tsunami, or track its motion where in situ buoy data is not available.

In the context of the International GNSS Service (IGS), several IGS Ionosphere Associated Analysis Centers (IAAC) have developed different techniques to provide Global Ionospheric Maps (GIMs) of Vertical Total Elec-