Comparison of the measured and modeled electron densities and temperatures in the ionosphere and plasmasphere during 14–16 May 1991

Abstract

The electron density and temperature in the ionosphere and plasmasphere measured by the Millstone Hill incoherent-scatter radar and the instruments on board of the EXOS-D satellite are compared with calculations from a time-dependent mathematical model of the Earth's ionosphere and plasmasphere during 14–16 May 1991. Use of [O]/[N 2] correction factors with the NRLMSISE-00 model of the neutral atmosphere was found to bring the modeled and measured F-region main peak electron densities into agreement. It was found that the nighttime additional heating rate should be added to the normal photoelectron heating in the electron energy equation, in the nighttime plasmasphere region, in order for the model to reproduce the observed high plasmaspheric electron temperature within the Millstone Hill magnetic field flux tube in the Northern Hemisphere. The additional heating brings the measured and modeled electron temperatures into agreement in the plasmasphere and into a very large disagreement in the ionosphere, if the classical electron heat flux along magnetic field lines is used. An approach of Pavlov et al. (2000, 2001) based on a new effective electron thermal conductivity coefficient along the magnetic field line and the evaluated additional heating of electrons in the plasmasphere is used to explain the observed electron temperature in the ionosphere and plasmasphere. This approach leads to a heat flux which is less than that given by the classical theory. The effects of the additional plasmaspheric heating of electrons on the electron temperature and density are small at the F-region altitudes if the modified electron heat flux is used. We found that the resulting effect of vibrationally excited N 2 and O 2 on NmF2 is the decrease of the calculated NmF2 by up to a factor of about 2.7 by day and up to a factor of about 2.5 by night. The modeled electron temperature is very sensitive to the electron density, and this decrease in electron density results in an increase of the calculated daytime electron temperature up to about 960 K at the F-region main peak altitude giving closer agreement between the measured and modeled electron temperatures. Both the daytime and nighttime electron densities and temperatures are not reproduced by the model without vibrationally excited N 2 and O 2, and inclusion of vibrationally excited N 2 and O 2 brings the model and data into agreement. The model with including vibrationally excited N 2 and O 2 in the loss rate of O +( 4 S) ions produces ion temperatures close to those given by the middle latitude model without including vibrationally excited N 2 and O 2. The detailed investigation of the ionospheric electron energy balance was carried out. It is shown for the first time that the revised electron cooling rates derived by Pavlov (1998a, c), and Pavlov and Berrington (1999), and Lobzin et al. (1999) produce a better fit of the calculated electron temperature and density to the radar data than the outdated cooling rates of Schunk and Nagy (1978). Revised (decreased) electron cooling rates increase the electron temperature and decrease the electron density. The difference between the revised and outdated cooling rates of thermal electrons leads to the maximum difference of 230 K between the calculated electron temperatures at the F2-peak altitude and to the increase of the calculated F-region main peak electron density by up to a factor of 1.13. Contrary to previous studies given by Richards (1986), Richards and Khazanov (1997), and Aponte et al. (1999), we found that the resulting effect of N( 2 D) electron quenching included in thermal electron heating on the electron temperature at the F2 peak altitude is the very weak increase of the calculated electron temperature up to about 35 K . It is found that the effect of including the N( 2 D) diffusion results in a decrease in the calculated daytime N( 2 D) number density above about 290 km and in a decrease of the daytime integral intensity at 520 nm up to a factor of 1.11.