Empirical Models of Plasma Parameters of the Mesosphere

The mesosphere is an altitude region which is only accessible for in-situ measurements by means of sounding rockets. Hence data from that region are by nature sporadic and even IRI (= International Reference Ionosphere) as the most ambitious effort to describe the density of free electrons has not paid the same attention to the lower ionosphere as to higher regions. This project aims at establishing representative empirical models of parameters of the lower ionosphere which are either inadequately described by IRI or not at all part of it: the transition from molecular to cluster ions, the density of negative ions, and the effective recombination rate. These parameters will then provide useful tools for atmospheric modellers and they can e.g. provide reasonable density limits of trace constituents. For electron densities two initially separate models are envisaged, one for non-auroral latitudes and the other for the auroral zone. The former will be a description as a function of solar zenith angle, latitude, season and solar activity as the determining inputs, whereas for geomagnetically high latitudes primarily solar zenith angle and the degree of disturbance, expressed in local riometer absorption, will be used. Electron density measurements in the lower ionosphere obtained by reliable methods (wave propagation, incoherent scatter radars) will be combined to take advantage of both the accurate, but few (about 100) wave propagation data from sounding rockets down to low altitudes and the large number of radar profiles (over 30,000) which has become available recently. In order to anticipate the required mathematical formulation to describe the various variations, the theoretical (ion-chemical) model available at the Institute is to be upgraded. Differences between the theoretical and the empirical models will be addressed, and implications pertaining to the neutral atmosphere will be investigated. From the full model the important practical parameters effective recombination rate and mean ion mass shall be established. The models shall be developed in a PC environment, using Matlab as the primary software tool. The development work and scientific analysis of the results shall be carried out in the same environment. For the implementation of the models as part of IRI at NASA Goddard they have to be ported to Unix/Fortran and adapted for the operational environment at the site.