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Alternate Methods for Calculating Microwave Absorption in Jovian Auroral Ionosphere

Presentation #324.03 in the session Giant Planet Magnetospheres, Ionospheres and Aurorae (Poster + Lightning Talk)

Published onOct 23, 2023
Alternate Methods for Calculating Microwave Absorption in Jovian Auroral Ionosphere

Data from JUNO’s Microwave Radiometer (MWR) indicates a drop in microwave radiation over the densest aurora regions over nearly all of the 52 perijoves observed so far. These auroral “cold spots’ were mainly observed in Channel 1 (0.6GHz) of the MWR, but present in Channel 2 and 3 at higher frequencies with less relative intensity. This inverse relationship between auroral brightness reduction and frequency indicates that cold spots may be plasma related.

Previous work by Hodges et al. (2021) attributes the cold spots to reflection in auroral ionosphere which require large electron densities in the range of 3×1015m-3, far exceeding existing results for measured electron densities in the Jovian ionosphere. (See e.g., Hinson et al., 1998). An alternative is a cold plasma model with reflections over multiple layers (Hodges et al., 2021), but this would require hundreds of layers, considered improbable.

In this work, we demonstrate that the opacity in Jovian aurora could be primarily explained by an auroral ionization layer in lower ionosphere at altitudes of approximately 150 km above the 1 bar pressure level where a high electron collision frequency can cause high opacity, even with a relatively thin ionization layer and low electron density as consistent with existing results. This is similar to conditions in the Earth’s aurora layer (Mannuci et al., 2015). This presentation will also describe the relationship of cold spot intensity and electron density over different MWR channels.

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