Juno's UV auroral spectral imaging, ionospheric conductance and infrared (H3+) atmospheric cooling.

NASA’s Juno spacecraft has been orbiting Jupiter on a highly elliptical orbit since 2016. Its payload includes both in situ (magnetic field, energetic charged particles) and remote sensing (ultraviolet, infrared) instruments. Among the sensors on board the UltraViolet Spectrograph (UVS) and the Jovian Infrared Auroral Mapper (JIRAM) observe the morphology and the spectral characteristics of the aurora. The UV emission is caused by collisionally excited H2 emissions while the infrared aurora in the spectral window of the JIRAM L-band imager includes some of the brightest H3+ thermal features between 3.3 and 3.6 μm. JIRAM’s spatial resolution is up to 50 km/pixel while UVS has a resolution of about 750 km. The UVS instrument provides spectral images between 70 and 200 nm that are used to quantify the auroral electron precipitation and estimate the mean energy of the auroral electrons. The combination of the global UV auroral brightness and electron mean energy makes it possible to remotely derive two-dimensional global maps of the precipitated electron flux. This information is used as an input to a photochemical model to calculate the ionospheric composition associated with each pixel, including the H3+ vertical and horizontal ion distribution. We shall explain how maps of the Pedersen conductance, a key quantity in the magnetosphere-ionosphere-thermosphere coupling, are built for each Juno perijove in both hemispheres. Comparisons have shown that the global conductances are nearly equal in the north and the south, contrary to the field-aligned current densities measured by Juno.
Occasionally, UVS and JIRAM collect concurrent auroral images of the north or south aurora. In a second part of the seminar, we show how these observations may be combined to simultaneous assess the electron collisional heating of the heat equation and the thermostatic effect of H3+ radiative cooling to space. These two terms are part of the global energy balance of the Jovian upper atmosphere and must be considered to solve the ‘energy crisis’ associated with the unexpectedly high thermospheric temperature of Jupiter. We also demonstrate that our model based on the ultraviolet spectral images provides a good a priori estimate of the infrared cooling power. NASA’s Juno spacecraft has been orbiting Jupiter on a highly elliptical orbit since 2016. Its payload includes both in situ (magnetic field, energetic charged particles) and remote sensing (ultraviolet, infrared) instruments. Among the sensors on board the UltraViolet Spectrograph (UVS) and the Jovian Infrared Auroral Mapper (JIRAM) observe the morphology and the spectral characteristics of the aurora. The UV emission is caused by collisionally excited H2 emissions while the infrared aurora in the spectral window of the JIRAM L-band imager includes some of the brightest H3+ thermal features between 3.3 and 3.6 μm. JIRAM’s spatial resolution is up to 50 km/pixel while UVS has a resolution of about 750 km.
The UVS instrument provides spectral images between 70 and 200 nm that are used to quantify the auroral electron precipitation and estimate the mean energy of the auroral electrons. The combination of the global UV auroral brightness and electron mean energy makes it possible to remotely derive two-dimensional global maps of the precipitated electron flux. This information is used as an input to a photochemical model to calculate the ionospheric composition associated with each pixel, including the H3+ vertical and horizontal ion distribution. We shall explain how maps of the Pedersen conductance, a key quantity in the magnetosphere-ionosphere-thermosphere coupling, are built for each Juno perijove in both hemispheres. Comparisons have shown that the global conductances are nearly equal in the north and the south, contrary to the field-aligned current densities measured by Juno.
Occasionally, UVS and JIRAM collect concurrent auroral images of the north or south aurora. In a second part of the seminar, we show how these observations may be combined to simultaneous assess the electron collisional heating of the heat equation and the thermostatic effect of H3+ radiative cooling to space. These two terms are part of the global energy balance of the Jovian upper atmosphere and must be considered to solve the ‘energy crisis’ associated with the unexpectedly high thermospheric temperature of Jupiter. We also demonstrate that our model based on the ultraviolet spectral images provides a good a priori estimate of the infrared cooling power.