In these blocks the corresponding continuity, momentum, and heat balance
equations for the neutral, electron, and ion gases, as well as the equation for
the electric field potential, are solved numerically by the use of the finite-
difference methods, using different coordinate systems and different spatial grids
of numerical integration. The height steps of numerical integration are variable,
from 1-3 km at heights below 100 km to 30 km and more at heights above 400 km.
A spherical geomagnetic coordinate system is used in the neutral atmosphere and
lower ionosphere block and a geomagnetic dipole coordinate system is used in the
other blocks. The exchange of information between the blocks is carried out at
every time step of the numerical integration of the modeling equations.
Neutral Atmosphere and Lower Ionosphere Block
In the neutral atmosphere section of this block, the neutral gas temperature T n ,mass
density , thermospheric wind velocity vector V , and number densities n n of the
main neutral gas components N 2 ,O 2 , and O are calculated for the height range from
60 to 520 km using the spherical geomagnetic coordinate system. We can perform
our calculations either by solving the full system of hydrodynamic equations for
the neutral gas or by using empirical thermospheric models such as MSISE-90
(Hedin et al. 1991 ) and its later modifications NRLMSISE-00 (Picone et al. 2002 )to
calculate the temperature and number densities of the main neutral gas components.
In all cases the three-dimensional thermospheric circulation is calculated from the
solution of the momentum and continuity equations.
The following system of the continuity, momentum, and energy balance equa-
tions for the neutral gases is solved in the fully self-consistent variant:
@n n =@t Cr Œn n . V C V dn / D Q n L n
Œ@ V =@t C . V ; r / V C 2 ˝ V hor
D . r p/ hor X
ni ni n n . V V i / hor C . r
V / hor ;
g D @p=@r
@=@t Cr . V / D 0
n n m n