  Developing a quantitative understanding of wave plasma processes in the lower
ionosphere requires a reasonably accurate theoretical description of the
underlying physical processes. For such highly collisional plasma environment
as the E-region ionosphere, kinetic theory represents the most accurate
theoretical description of wave processes. For the analytical treatment,
however, the collisional kinetic theory is extremely complicated and succeeds
only in a limited number of physical problems. To date, most research applied
oversimplified fluid models that lack a number of critical kinetic aspects, so
that the coefficients in the corresponding fluid equations are often accurate
only to an order of magnitude. This paper presents the derivation for the
highly collisional, partially magnetized case relevant to E-region conditions.
It provides a more accurate reduction of the ion and, especially, electron
kinetic equations to the corresponding 5-moment fluid equations by using a new
set of analytic approximations. This derivation results in more accurate
fluid-model set of equations appropriate for most E-region problems. The
results of this paper could be used for a routine practical analysis when
working with actual data. The improved equations can also serve as a basis for
more accurate plasma fluid computer simulations.
