Abstract. This study compares the Isis II satellite measurements of the electron density and temperature, the integral airglow intensity and volume emission rate at 630 nm in the SAR arc region, observed at dusk on 4 August, 1972, in the Southern Hemisphere, during the main phase of the geomagnetic storm. The model results were obtained using the time dependent one-dimensional mathematical model of the Earth's ionosphere and plasmasphere (the IZMIRAN model). The major enhancement to the IZMIRAN model developed in this study to explain the two component 630 nm emission observed is the analytical yield spectrum approach to calculate the¯uxes of precipitating electrons and the additional production rates of Nand O 2 ions, and O 1 h in the SAR arc regions in the Northern and Southern Hemispheres. In order to bring the measured and modelled electron temperatures into agreement, the additional heating electron rate of 1X05 eV cm À3 s À1 was added in the energy balance equation of electrons at altitudes above 5000 km during the main phase of the geomagnetic storm. This additional heating electron rate determines the thermally excited 630 nm emission observed. The IZMIRAN model calculates a 630 nm integral intensity above 350 km of 4.1 kR and a total 630 nm integral intensity of 8.1 kR, values which are slightly lower compared to the observed 4.7 kR and 10.6 kR. We conclude that the 630 nm emission observed can be explained considering both the soft energy electron excited component and the thermally excited component. It is found that the inclusion of N 2 v b 0 and O 2 v b 0 in the calculations of the O 4 loss rate improves the agreement between the calculated N e and the data on 4 August, 1972. The N 2 v b 0 and O 2 v b 0 eects are enough to explain the electron density depression in the SAR arc F-region and above F2 peak altitude. Our calculations show that the increase in the O N 2 rate factor due to the vibrationally excited nitrogen produces the 5±19% reductions in the calculated quiet daytime peak density and the 16± 24% decrease in NmF2 in the SAR arc region. The increase in the O N 2 loss rate due to vibrationally excited O 2 produces the 7±26% decrease in the calculated quiet daytime peak density and the 12±26% decrease in NmF2 in the SAR arc region. We evaluated the role of the electron cooling rates by low-lying electronic excitation of O 2 1 D g and O 2 1 R g , and rotational excitation of O 2 , and found that the eect of these cooling rates on e can be considered negligible during the quiet and geomagnetic storm period 3±4 August, 1972. The energy exchange between electron and ion gases, the cooling rate in collisions of O 3 with thermal electrons with excitation of O 1 h, and the electron cooling rates by vibrational excitation of O 2 and N 2 are the largest cooling rates above 200 km in the SAR arc region on 4 August, 1972. The enhanced IZMIRAN model calculates also number densities of N 2 f 3 P g Y N 2 g 3 P u , and N 2 e 3 R u at several vibrational levels, O 1 , and the volume emission rate and integr...