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GITM (25.11)

Global Ionosphere Thermosphere Model (GITM)

Model Description

The Global Ionosphere Thermosphere Model (GITM) is a three-dimensional, non-hydrostatic model of the Earth's thermosphere and ionosphere system. Unlike many thermosphere-ionosphere models that use pressure coordinates and assume hydrostatic equilibrium, GITM uses an altitude-based spherical grid and explicitly solves the full vertical momentum equation, allowing realistic simulation of vertical dynamics, gravity-wave propagation, and auroral-region upwelling.

GITM solves the coupled continuity, momentum, and energy equations for both neutral and ion species. The standard Earth configuration includes major neutral species O, O2, N2, NO, N(4S), and He, along with additional excited neutral states and ion species including O+, O2+, NO+, N2+, N+, and He+. The model includes separate vertical velocities for individual neutral species and incorporates neutral-neutral frictional coupling, semi-implicit chemistry, ion-neutral coupling, ionospheric electrodynamics, EUV heating, auroral precipitation effects, and thermal conduction.

GITM supports both global and regional simulations with flexible horizontal resolution and a stretched vertical grid extending from approximately 90 km to 600 km altitude. The model can operate in one-dimensional, regional, or fully global configurations. It uses MPI-based domain decomposition for high-performance parallel computing and dynamically adjusts its time step according to local velocities, sound speed, and grid spacing.

The model includes multiple options for high-latitude electrodynamic forcing, including Weimer, AMIE, SWMF, and OVATION Prime drivers. Auroral precipitation can include diffuse, monoenergetic, broadband, and ion aurora using Fang et al. parameterizations. Solar EUV forcing may be specified using FISM/FISM2 irradiance spectra, including eclipse and nightside irradiance capability.

GITM has been extensively validated against multiple observational data sets, including GOCE thermospheric densities and winds, GUVI O/N2 composition ratios, and GNSS total electron content (TEC) observations during geomagnetic storm periods.

GITM uses a flexible stretched grid system in latitude, longitude, and altitude, allowing users to configure the spatial resolution according to the scientific application and computational resources available. Current CCMC production runs use a horizontal resolution of 1° in latitude and 4° in longitude.

Model Figure(s) :

Model Inputs Description

Solar EUV irradiance (F10.7 and FISM2 spectral irradiance)
Interplanetary Magnetic Field (IMF)
Solar wind velocity and density
Auroral electrojet (AE) indices
High-latitude electric potential models (e.g., Weimer05 (default), AMIE, SWMF)
Auroral precipitation models (e.g., Feature Tracking of Aurora (FTA; default), Fuller-Rowell and Evans, OVATION Prime)
Initial atmospheric specification: Empirical atmosphere (MSIS/IRI)
Lower boundary tidal forcing and wave specification: MSIS

Model Outputs Description

Neutral temperature
Ion temperature
Electron temperature
Neutral winds: zonal, meridional, vertical
Plasma velocities: zonal, meridional, field-aligned/vertical
Neutral mass density (kg/m³)
Number densities of neutral species: O, O2, N2, NO, N(4S), He
Number densities of ion species: O+, O2+, NO+, N2+, N+, He+
Electron density (m⁻³)
Total Electron Content (TEC)
O/N2 composition ratio
Joule heating
EUV heating
Chemical heating rates
Electric potential and ionospheric conductances
Auroral energy deposition and ionization rates

Model Caveats

GITM is typically limited to altitudes below approximately 600 km and does not fully represent the plasmasphere; therefore, global TEC can be underestimated.
Numerical diffusion and boundary-condition assumptions can affect the development of small-scale structures and wave propagation.
Model results are sensitive to high-latitude electrodynamic drivers, auroral precipitation specification, and lower-boundary tidal forcing.
Different empirical forcing models (e.g., Weimer, AMIE, OVATION Prime) can produce substantially different thermosphere-ionosphere responses.
The model uses parameterized photoelectron heating and auroral energy deposition schemes rather than fully kinetic treatments.
Some ion species are solved chemically but are not fully advected.
Validation studies indicate that GITM may overestimate O/N2 ratios and daytime TEC while underestimating nighttime TEC during some geomagnetic storm conditions (Ridley et al., 2026).

Change Log

May 18, 2026: GITM version 25.11 is available on the CCMC ROR system.
 Please see the changes being compared in GITM's public repository on GitHub between this version and the previous version, 23.01.01.

 

 

Model Acknowledgement/Publication Policy (if any)

Ridley, A. J., Wu, C., Bukowski, A., & Bell, J. (2026). Updates, examples and validation of the global ionosphere thermosphere model. Space Weather, 24, e2025SW004925. https://doi.org/10.1029/ 2025SW004925

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Curator: Chiu Wiegand | NASA Official: Dr. Masha Kuznetsova | Privacy and Security Notices | Accessibility | CCMC Data Collection Consent Agreement