Do describe the coronal plasma we use the MHD equations:
Here, P stands for the plasma pressure,
for the magnetic field, 
for the
plasma density,
for the solar gravitational potential, 
for the plasma velocity,
for the electric field,
R is the gas constant,
T the temperature, 
the current density, 
the
resistivity and 
the vacuum permeability. We normalize
the magnetic field
by a typical value 
, the plasma pressure p by
,
the mass density 
by 
,
the length L by a solar radius and the current density
by 
, the plasma bulk velocity by the Alfven velocity 
, the
electric field by 
, the time by the Alfven time and the resistivity
by 
.
