Latitudinal Profiles of the Jovian IR Emissions of H+3 at 4 μm with the NASA Infrared Telescope Facility: Energy Inputs and Thermal Balance

We present ground-based observations of the jovian ionospheric H+3 emission at 4 micrometers, using the CSHELL facility long-slit spectrograph at the NASA Infrared Telescope Facility (IRTF) in Hawaii. The data were obtained during four consecutive nights from July 13 to July 16, 1996. The 30-arcsec length slit of the spectrograph was aligned with the jovian CML, in order to get high-spatial, high-spectral resolution latitudinal profiles of the jovian H+3 emission. A self-consistent multi-emission-component (MEC) model, developed for the analysis of these latitudinal profiles, simulates the emission from the vertical distribution of the ionization components known to produce H+3. We initially identify these as solar-EUV photo-ionization, auroral oval precipitation, and diffuse auroral precipitation. A fourth component, mid-to-low (MTL)-latitude ionization is derived, and then fitted. InfraRed H+3 auroral ovals follow closely the UV ovals as observed with the HST instruments WFPC2 and FOC. Our model shows that the auroral production rate is generally between a few and a few tens of times the EUV rate. The MTL component production rate is 1 to 40% of the auroral rate in the north, and 2 to 16% in the south. Input and output energies are scaled to solar EUV values. We assume an EUV insolation of 60 μW/m2, equivalent to a total jovian EUV insolation of 1012W. Scaled to the EUV input, planetwide integration of the components of our model produces the total hemispheric energy inputs associated with the aurora, the diffuse emission, and the MTL emission. The results are 1.22(±.25)×1012W, 0.37(±.15)×1012W, and 0.65(±.32)×1012W, respectively, for the north and 1.15(±.30)×1012W, 0.21(±.10)×1012W, and 0.64 (±.32)×1012W for the south, respectively. We discusss the limitations of our scaling process, introducing the notion of emission efficiency with respect to a nominal 1000K/LTE H+3 emitter. The overall auroral emission is approximately 43 (+107, −23)% of that measured in 1993. Our results show that H+3 controls the energy balance of the auroral regions above the homopause, as well as the equatorial regions.