A Novel Method to Derive Exospheric Temperatures from Swarm Thermospheric Densities during Quiet Times

One of the most important parameters in the atmosphere, the neutral temperature, becomes difficult to measure at high altitudes such as the exosphere. Therefore, based on the assumption of static equilibrium and isothermal atmosphere, a new method was developed to derive quiet-time exospheric temperatures using neutral atmospheric densities from 470 km to 550 km, which were obtained from the Swarm satellites. The derived neutral temperatures were obtained at an altitude of approximately 500 km in the low and middle latitudes from mid-April 2014 to early August 2014. The results were evaluated with nighttime temperatures from ground-based Fabry Perot Interferometers at 250 km. The mean deviation between the derived temperatures and FPI was 30.80 K and the standard deviation of the mean was 106.20 K. The diurnal variations of the exospheric temperatures, which tended to reach their maximum in the late afternoon, were in good consistency with the NRL-MSISE00 model simulations. This novel method performs well at low and middle latitudes. The greatest source of uncertainty is the mean molecular mass, which is also not well determined at these high altitudes. Hence, a measurement called “Satellite-tethered Mass Spectrometer Detection” was proposed to address this.