EFFECT OF NO TRANSPORT ON RADIO-WAVE ABSORPTION

Global determinations of the response of radio wave absorption in the ionosphere to changes in the solar zenith angle show that this respons e is relatively weak in winter compared to that in summer and equinox in non-equatorial regions. In a bid to understand this behaviour, a nu merical simulation of the response has been attempted employing solsti ce and equinox electron density profiles derived from minor neutral sp ecies concentrations of a zonally averaged photochemical-transport tim e-dependent model of the middle atmosphere, ion chemistry and solar ir radiance fluxes. The results have established that the seasonal variat ion in the response is related to seasonally and latitudinally varying nitric oxide abundance in the mesosphere resulting from corresponding changes in its chemistry and transport.