Movie Caption: This movie shows the SAMI3 delta total electron content (TEC) and the propagation of traveling ionospheric disturbances over the continental U.S. during a severe weather event in April 2014. (Courtesy of Sarah McDonald, NRL).
Model Description: The Naval Research Laboratory (NRL) SAMI3 (Sami3 is Also a Model of the Ionosphere) is a comprehensive, physics-based, global model of the ionosphere developed at NRL. SAMI3 is based on SAMI2 (Huba et al., 2000), a two-dimensional model of the ionosphere. SAMI3 models the plasma and chemical evolution of seven ion species (H+, He+, N+, O+, N2+, NO+ and O2+) in the altitude range extending from 70 km to ~8 Re (Earth radii) and magnetic latitudes up to ±88°. SAMI3 solves the ion continuity and momentum equations for all seven of the ion species, and solves the complete temperature equations for the electrons and three ion species (H+, He+ and O+). Ion inertia is included in the ion momentum equation for motion along the geomagnetic field. SAMI3 uses a fixed, non-uniform grid defined in the magnetic coordinate system. One axis of the grid is aligned with the Earth’s geomagnetic field, allowing the model to distinguish between motion along the magnetic field and perpendicular to the magnetic field. The other two grid axes define magnetic east and the vector perpendicular to the magnetic field lines in the radial direction. SAMI3 can be configured to use a tilted dipole model of Earth’s geomagnetic field or a spherical harmonic representation of Magnetic Apex coordinates (Emmert et al., 2010; Richmond, 1995), which includes the International Geomagnetic Reference Field (IGRF) representation of the geomagnetic field.
The SAMI3 electric fields are solved self-consistently by solving a two-dimensional electrostatic potential equation that is derived from current conservation in magnetic (currently magnetic-dipole) coordinates, and including gravity-driven currents. The perpendicular electric field is used in SAMI3 to calculate the mid- and low-latitude E × B drifts (Huba et al., 2008; 2010). The high-latitude region is electrodynamically coupled to the magnetosphere as a result of the interaction of the magnetized solar wind with Earth’s geomagnetic field. To account for ion motion in the polar region, we have included a high-latitude electric potential from the Weimer-2005 model (Weimer, 2005), which is an empirical model that calculates how the polar electric potential responds to changes in the solar wind and interplanetary magnetic field (IMF). Solar extreme ultraviolet (EUV) irradiances are specified using either the NRL Solar Spectral Irradiance (NRLSSI) model (Lean et al., 2010) or using the EUV flux model for Aeronomic Calculations (EUVAC; Richards et al., 1994). In its standard configuration, SAMI3 uses NRL Mass Spectrometer Incoherent Scatter (NRLMSIS 2.0) climatology (Emmert et al., 2021) to specify thermospheric composition and neutral temperature, and the Horizontal Wind Model (HWM14) (Drob et al., 2015) to specify the zonal and meridional thermospheric winds.
SAMI3 has been used to study the impact of Medium Scale Traveling Ionospheric Disturbances (MSTIDs). The model is driven by specifications of the neutral atmosphere that include forcing from below to quantify the effect of the wave perturbations on the ionosphere. Perturbed thermospheric gravity wave fields are used to drive MSTIDs in the SAMI3 ionosphere model.
References: Drob, D. P., et al. (2015). An update to the Horizontal Wind Model (HWM): The quiet time thermosphere, Earth and Space Science, 2, 301–319, doi:10.1002/2014EA000089.
Emmert, J. T., A. D. Richmond, and D. P. Drob (2010). A computationally compact representation of Magnetic-Apex and Quasi-Dipole coordinates with smooth base vectors, J. Geophys. Res., 115, A08322, doi:10.1029/2010JA015326.
Emmert, J. T., Drob, D. P., Picone, J. M., Siskind, D. E., Jones, M. Jr., Mlynczak, M. G., et al. (2020). NRLMSIS 2.0: A whole‐atmosphere empirical model of temperature and neutral species densities. Earth and Space Science, 7, e2020EA001321. https://doi.org/ 10.1029/2020EA001321.
Huba, J.D., G. Joyce, and J.A. Fedder (2000). Sami2 is Another Model of the Ionosphere (SAMI2): A new low-latitude ionosphere model. J. Geophys. Res., 105, 23,035-23,053.
Huba, J. D., G. Joyce, and J. Krall (2008). Three- dimensional equatorial spread F modeling, Geophys. Res. Lett., 35, L10102, doi:10.1029/2008GL033509.
Huba, J. D., and G. Joyce (2010). Global modeling of equatorial plasma bubbles, Geophys. Res. Lett., 37, L17104, doi:10.1029/2010GL044281.
Lean, J. L., T. N. Woods, F. G. Eparvier, R. R. Meier, D. J. Strickland, J. T. Correira, and J. S. Evans (2010). Solar Extreme Ultraviolet Irradiance: Present, Past and Future, J. Geophys. Res., doi:10.1029/2010JA015901.
Richmond, A. (1995). Ionospheric electrodynamics using magnetic APEX coordinates. J. Geomag. Geoelectr., 47, 191-212.
Solomon, S. C., and L. Qian, 2005. Solar extreme-ultraviolet irradiance for general circulation models, J. Geophys. Res., 110, A10306, doi: 10.1029/2005JA011160
Weimer, D. R. (2005). Improved ionospheric electrodynamic models and application to calculating Joule heating rates, J. Geophys. Res., 110, A05306, doi:10.1029/2004JA010884.
Zawdie, K.A., S.E. McDonald, S. Eckermann, D. Broutman, and F. Sassi, 2018. Simulating MSTIDs Generated from Tropospheric Weather. COSPAR, Pasadena, CA, July 15-21, 2018.
Zawdie, K.A., S.E. McDonald, S. Eckermann, D. Broutman, and F. Sassi, 2018b. The Impact of Gravity Wave Signatures in Thermospheric Winds on the Ionosphere. CEDAR Workshop, Santa Fe, NM, June 25-29, 2018.
Zawdie, K.A., S.E. McDonald, S. Eckermann, D. Broutman, and F. Sassi, 2019. Comparing MSTIDs Generated from Tropospheric Weather to the Hooke Model. URSI NRSM, Boulder, CO, January 9-11, 2019.
