The Jupiter Thermospheric General Circulation Model (JTGCM) calculates the global dynamical structure of Jupiter's thermosphere self‐consistently with its global thermal structure and composition. The main heat source that drives the thermospheric flow is high‐latitude Joule heating. A secondary source of heating is the auroral process of particle precipitation. Global simulations of Jovian thermospheric dynamics indicate strong neutral outflows from the auroral ovals with velocities up to ∼1.2 km/s and subsequent convergence and downwelling at the Jovian equator. Such circulation is shown to be an important process for transporting significant amounts of auroral energy to equatorial latitudes and for regulating the global heat budget in a manner consistent with the high thermospheric temperatures observed by the Galileo probe. Adiabatic compression of the neutral atmosphere resulting from downward motion is an important source of equatorial heating from the top boundary of the JTGCM to 0.06 μbar. The adiabatic heating continues to dominate between 0.06 and 0.2 μbar, but with the addition of comparable heating due to horizontal advection induced by the meridional flow. Thermal conduction plays an important role in transporting heat down to lower altitudes (>0.2 μbar). The total heating transported in this region is radiated away by infrared hydrocarbon cooling via CH 4 (7.8 μm) and C 2 H 2 (12.6 μm) emissions.
Observations of Jupiter carried out by the Chandra Advanced CCD Imaging Spectrometer (ACIS‐S) instrument over 24–26 February 2003 show that the auroral X‐ray spectrum consists of line emission consistent with high‐charge states of precipitating ions, and not a continuum as might be expected from bremsstrahlung. The part of the spectrum due to oxygen peaks around 650 eV, which indicates a high fraction of fully stripped oxygen in the precipitating ion flux. A combination of the OVIII emission lines at 653 eV and 774 eV, as well as the OVII emission lines at 561 eV and 666 eV, are evident in the measure auroral spectrum. There is also line emission at lower energies in the spectral region extending from 250 to 350 eV, which could be from sulfur and/or carbon. The Jovian auroral X‐ray spectra are significantly different from the X‐ray spectra of comets. The charge state distribution of the oxygen ions implied by the measured auroral X‐ray spectra strongly suggests that independent of the source of the energetic ions, magnetospheric or solar wind, the ions have undergone additional acceleration. This spectral evidence for ion acceleration is also consistent with the relatively high intensities of the X rays compared with the available phase space density of the (unaccelerated) source populations of solar wind or magnetospheric ions at Jupiter, which are orders of magnitude too small to explain the observed emissions. The Chandra X‐ray observations were executed simultaneously with observations at ultraviolet wavelengths by the Hubble Space Telescope and at radio wavelengths by the Ulysses spacecraft. These additional data sets suggest that the source of the X rays is magnetospheric in origin and that the precipitating particles are accelerated by strong field‐aligned electric fields, which simultaneously create both the several‐MeV energetic ion population and the relativistic electrons observed in situ by Ulysses that are correlated with ∼40 min quasi‐periodic radio outbursts.
On day 59 of 1987 a well calibrated set of photometric observations of auroral emissions (427.8, 630.0, 844.6, and 871.0 nm) was obtained at Sondre Stromfjord, Greenland coincident with incoherent scatter radar measurements of electron density. Ratios of these optical emissions were used to correct for atmospheric extinction and to infer the average energy of the precipitating electrons and the deviations in the atmospheric composition induced by auroral heating. Previously, the radar data taken alone had been used to infer the average energy of the auroral particles. For the first time a comparison is made of the results from this optical ratio technique with those obtained by combining the optical data with the radar data and with results obtained using the radar data alone. Specifically, we compare the average energy inferred by these techniques as well as the changes in the atomic oxygen to molecular nitrogen ratio in the lower thermosphere. This study shows the critical importance of characterizing the atmospheric scattering if reliable results are to be derived. In particular, it is shown that on occasion the optical technique may be even more reliable than using radar and optics together since, because of light scattering, the radar and the optics are sometimes observing different parts of the aurora. Magnetometer data are used to estimate local Joule heating. The combined data are also used to address the question of whether observed composition changes were produced locally.
