TIE-GCM

The NCAR Thermosphere-Ionosphere- Electrodynamics General Circulation Model (TIE-GCM) is a comprehensive, first-principles, three-dimensional, non-linear representation of the coupled thermosphere and ionosphere system that includes a self-consistent solution of the low-latitude electric field. The model solves the three-dimensional momentum, energy and continuity equations for neutral and ion species at each time step, using a semi-implicit, fourth-order, centered finite difference scheme, on each pressure surface in a staggered vertical grid. It has 33 constant-pressure levels in the vertical, extending from approximately 97 km to 1000 km in intervals of one-half scale height, and a 5° x 5° or 2.5° x 2.5° latitude-longitude grid, in its base configuration. The time step is 30-60 s.

Hydrostatic equilibrium, constant gravity, steady-state ion and electron energy equations, and incompressibility on a constant pressure surface, are assumed. Ion velocities are derived from the potential field created by combining the imposed magnetospheric potential with the low-latitude dynamo potential, and then calculating ion velocities from ExB drifts, rather than solving the ion momentum equations explicitly. Some minor species are not currently included in the model, including hydrogen and helium and their ions, and argon. Several parameterizations are used in the TIE-GCM: an empirical model is used to specify photoelectron heating; the production of secondary electrons is included using an empirical model derived from two-stream calculations, the effects of mixing by gravity waves are included using an eddy diffusion formulation; CO2 is included by specifying a lower boundary condition and assuming that it is in diffusive equilibrium. The upper boundary conditions for electron heat transfer and electron number flux are empirical formulations. At the lower boundary, atmospheric tides are specified using the Global Scale Wave Model (GSWM).

Solar EUV inputs: F107 (current daily F10.7 solar index) and F107A (81-day center-averaged F10.7 solar index)

Particle precipitation: Hemispheric Power in GW, obtained from 3-hour Kp index

Ionospheric electric fields at high latitudes: Provided by Heelis model and Weimer model.

Inputs for Heelis model: Cross polar cap potential in kV, obtained from 3-hour Kp index Hemispheric Power in GW, obtained from 3-hour Kp index Optional (not implemented): y-component of the interplanetary magnetic field (By) in nT

Inputs for Weimer model: Interplanetary magnetic field, By and Bz, in nT Solar wind density and speed, ρ and v, in cm-3 and km s-1

Inputs for lower boundary: Diurnal and semi-diurnal migrating tides, specified by the GSWM

Primary timed-dependent output fields, specified in latitude, longitude, and pressure level: Geopotential height: Height of pressure surfaces (cm) Temperatures: Neutral, ion, electron (K) Neutral winds: zonal, meridional, (cm s-1), vertical (s-1) Composition: O, O2, NO, N(4S), N(2D) (mass mixing ratios - dimensionless) Ion and electron densities: O+, O2+, Ne (cm-3), (NO+ is calculated from Ne - (O+ + O2+)) Electric potential: (V) Other fields are available as secondary histories which can be set as needed.