THE EFFECTS OF NITRIC-OXIDE COOLING AND THE PHOTODISSOCIATION OF MOLECULAR-OXYGEN ON THE THERMOSPHERE IONOSPHERE SYSTEM OVER THE ARGENTINE ISLANDS/

In the past the global, fully coupled, time-dependent mathematical mod el of the Earth's thermosphere/ionosphere/plasmasphere (CTIP) has been unable to reproduce accurately observed values of the maximum plasma frequency, foF2, at extreme geophysical locations such as the Argentin e Islands during the summer solstice where the ionosphere remains in s unlight throughout the day. This probably because the This seasonal de pendence of thermospheric cooling by 5.3 mu m nitric oxide has been ne glected and the photodissociation of O-2 and heating rate calculations have been over-simplified. Now we have included an up-to-date calcula tion of the solar EUV and UV thermospheric heating rate, coupled with a new calculation of a photodissociation rate, in the model. Seasonall y dependent 5.3 Irm nitric oxide cooling is also included. With these important improvements, it is found that model values of foF2 are in s ubstantially better agreement with observation. The height of the F2-p eak is reduced throughout the day, but remains within acceptable limit s of values derived from observation, except at around 0600 h LT. We a lso carry out two studies of the sensitivity of the upper atmosphere t o changes in the magnitude of nitric oxide cooling and photodissociati on rates. We find that hmF2 increases with increased heating, whilst f oF2 falls. The converse is true for an increase in the cooling rate. S imilarly increasing the photodissociation rate increases both hmF2 and foF2. These changes are explained in terms of changes in the neutral temperature, composition and neutral wind.