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We present a comparison of the observed behavior of the F region ionosphere over Millstone Hill during the geomagnetically quiet and storm period on 16-23 March, 1990, with numerical model calculations from the time-dependent mathematical model of the Earth's ionosphere and plasmasphere. The effects of vibrationally excited N₂(<i>v</i>) and O₂(<i>v</i>) on the electron density and temperature are studied using the N₂(<i>v</i>) and O₂(<i>v</i>) Boltzmann and non-Boltzmann distribution assumptions. The deviations from the Boltzmann distribution for the first five vibrational levels of N₂(<i>v</i>) and O₂(<i>v</i>) were calculated. The present study suggests that these deviations are not significant at vibrational levels <i>v</i> = 1 and 2, and the calculated distributions of N₂(<i>v</i>) and O₂(<i>v</i>) are highly non-Boltzmann at vibrational levels <i>v</i> &gt; 2. The N₂(<i>v</i>) and O₂(<i>v</i>) non-Boltzmann distribution assumption leads to the decrease of the calculated daytime NmF2 up to a factor of 1.44 (maximum value) in comparison with the N₂(<i>v</i>) and O₂(<i>v</i>) Boltzmann distribution assumption. The resulting effects of N₂(<i>v</i> &gt; 0) and O₂(<i>v</i> &gt; 0) on the NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 2.8 (maximum value) for Boltzmann populations of N₂(<i>v</i>) and O₂(<i>v</i>) and up to a factor of 3.5 (maximum value) for non-Boltzmann populations of N₂(<i>v</i>) and O₂(<i>v</i>) . This decrease in electron density results in the increase of the calculated daytime electron temperature up to about 1040-1410 K (maximum value) at the F2 peak altitude giving closer agreement between the measured and modeled electron temperatures. Both the daytime and nighttime densities are not reproduced by the model without N₂(<i>v</i> &gt; 0) and O₂(<i>v</i> &gt; 0) , and inclusion of vibrationally excited N₂ and O₂ brings the model and data into better agreement. The effects of vibrationally excited O₂ and N₂ on the electron density and temperature are most pronounced during daytime.<br><br><b>Key words: </b>Ionosphere (ion chemistry and composition; ionosphere-atmosphere interactions; ionospheric disturbances)