Ionospheric Disturbances Generated by the 2015 Calbuco Eruption: Comparison of GITM‐R Simulations and GNSS Observations.

Volcanic eruptions provide broad spectral forcing to the atmosphere and understanding the primary mechanisms that are relevant to explain the variety in waveform characteristics in the Ionosphere‐Thermosphere (IT) is still an important open question for the community. In this study, Global Navigation Satellite System (GNSS) Total Electron Content (TEC) data are analyzed and compared to simulations performed by the Global Ionosphere‐Thermosphere Model with Local Mesh Refinement (GITM‐R) for the first phase of the 2015 Calbuco eruption that occurred on 22 April. A simplified source representation and spectral acoustic‐gravity wave (AGW) propagation model are used to specify the perturbation at the lower boundary of GITM‐R at 100 km altitude. Two assumptions on the propagation structure, Direct Spherical (DS) and Ground Coupled (GC), are compared to the GNSS data and these modeling specifications show good agreement with different aspects of the observations for some waveform characteristics. Most notably, GITM‐R is able to reproduce the relative wave amplitude of AGWs as a function of radial distance from the vent, showing acoustic dominant forcing in the near field (<500 km) and gravity dominant forcing in the far‐field (>500 km). The estimated apparent phase speeds from GITM‐R simulations are consistent with observations with ∼10% difference from observation for both acoustic wave packets and a trailing gravity mode. The relevance of the simplifications made in the lower atmosphere to the simulated IT response is then discussed. Plain Language Summary: The two eruption phases of the 2015 Calbuco volcanic event created atmospheric pressure and gravity disturbances that were measured as plasma disturbances in the earth's upper atmosphere by global navigation satellites. This study utilizes a fully self‐consistent global circulation model of the upper atmosphere, with a highly flexible resolution, to simulate and investigate our understanding of the coupled atmosphere‐plasma system in the event of a volcanic eruption. It is shown that the current methodology is capable of recreating important features of the observed upper atmospheric signals which include magnitude distributions, arrival times, and the relative contributions of pressure and gravity influenced waves as a function of distance from the volcano. Key Points: GNSS TEC data analysis for the first phase of the 2015 Calbuco eruption shows varied acoustic (A) and gravity (G) dominant perturbationsA simplified source representation and spectral A‐G wave model are used to drive GITM‐R to capture meso‐scale perturbations near the sourceThe relative amplitude and phase speeds of acoustic and gravity wave driven ionospheric disturbance are reproduced in GITM‐R simulations [ABSTRACT FROM AUTHOR]