Thermospheric and ionospheric structure of the southern hemisphere polar cap on October 21, 1981, as determined from Dynamics Explorer 2 satellite data

Abstract

The Dynamics Explorer satellite (DE 2) passed over the Southern Hemisphere polar cap on orbit 1174 between 2326 UT and 2345 UT on October 21, 1981. The altitude of the satellite over the polar cap ranged between 325 and 390 km, and the local times were about 2100 LT on the down leg and 0900 LT on the up leg portions of the orbit. The full complement of instruments on the DE 2 satellite were making measurements during this pass. The electron precipitation spectra detected at a pitch angle of 7.5° were averaged over 8‐s intervals (0.5° latitude), and these spectra were used in an auroral model to calculate the ionization rates below the satellite in an atmosphere determined from the neutral temperature and composition measurements. These vertical ionization rate profiles are combined with solar photoionization rate profiles and used in a photochemical equilibrium model with O+ diffusion to calculate the electron and ion densities below the satellite. The electron and ion temperatures are also calculated assuming a local thermal energy balance, and the temperatures and densities are used to calculate the parallel, Pedersen, and Hall electrical conductivities. The total neutral gas heating rate is also calculated from four main sources: (1) particle heating, (2) Joule heating, (3) solar EUV heating, and (4) solar Schumann‐Runge heating. The particle heating is determined by multiplying the particle ionization rate by a particle heating efficiency determined from earlier studies. Joule heating at the satellite altitude is determined from the calculated Pedersen conductivity and the relative difference between the measured ion drifts and the neutral winds. Below the satellite altitude the Joule heating is calculated using the winds from the National Center for Atmospheric Research, Boulder, Colo. (NCAR) thermospheric general circulation model (TGCM) and a mapping of the measured ion drift into the lower ionosphere. The TGCM winds are shown to be in reasonable agreement with the measured winds at the satellite height. For this satellite pass the height‐integrated Joule heating exceeds both the auroral particle heating and the solar heating rates over the entire magnetic polar cap. The neutral gas heating rates peak in the vicinity of the morning auroral oval where the electric field increases abruptly from typical polar cap values of 30 mV m−1 to a high of about 100 mV m−1 just poleward of the dayside cusp aurora. Comparisons are made between the ionospheric properties derived from orbit 1174 and the corresponding properties used as parameterizations for the TGCM.