Specification of Auroral Ionospheric Conductances Using SSUSI and GUVI UV Imagery
Abstract:The SSUSI and GUVI instruments provide high spatial resolution imagery of the auroral at many wavelengths simultaneously. In addition, each wavelength is exactly registered in space with every other wavelength observed enabling one to formulate a wide range of auroral, thermospheric and ionospheric products. In this talk we present the SSUSI and GUVI auroral conductance observations. The steps and assumptions in the conductance calculations are described. Typical conductance products are presented. We will also discuss the difference between the conductance and conductivity profile.
FUV optical instruments record the line-of-sight integrated radiance. The observed intensity depends on the integral along the line of sight of the volume emission. The volume emission rate depends on the flux of energetic electrons, the excitation cross section and the number density of the emitting species. At these wavelengths and for typical energies absorption of the FUV photons along the line of sight is not important. The flux of energetic electrons at any altitude depends on the characteristic or average energy of the energetic electrons at the top of the atmosphere and the atmospheric column and composition of that column traversed by the energetic electrons. These energetic electrons cause local ionization; thus, the volume excitation rate and the local ionization rate are related. In the E-region, ions are in local photochemical equilibrium so it is possible to calculate the height dependent ionization rate of E-region electron density profile which can be expressed in terms of conductivity.
A montage of SSUSI F16 auroral images is shown in the figure. We currently have 4 DMSP satellites imaging the aurora. The revisit time is about every 15 minutes. The spatial resolution is 8km (native) and 25kmx25km for sensor data records. We can readily resolve structures 25km and smaller with excellent SNR.