Jupiter's Temperature Structure: A Reassessment of the Voyager Radio Occultation Measurements

TL;DR

This study revisits Voyager radio occultation data to accurately determine Jupiter's atmospheric temperature at 1 bar, revealing a slight increase over previous estimates and indicating potential spatial temperature variations across latitudes.

Contribution

The paper provides a systematic digitization and reanalysis of Voyager temperature profiles using current atmospheric data, refining Jupiter's 1 bar temperature estimates.

Findings

Corrected temperature at 1 bar is up to 4 K higher than previous values.

Jupiter's tropospheric temperature may vary by up to 7 K across latitudes.

Revised temperature estimates improve models of Jupiter's interior and atmospheric dynamics.

Abstract

The thermal structure of planetary atmospheres is an essential input for predicting and retrieving the distribution of gases and aerosols, as well as the bulk chemical abundances. In the case of Jupiter, the temperature at a reference level - generally taken at 1 bar - serves as the anchor in models used to derive the planet's interior structure and composition. Most models assume the temperature measured by the Galileo probe (Seiff et al. 1998). However, those data correspond to a single location, an unusually clear, dry region, affected by local atmospheric dynamics. On the other hand, the Voyager radio occultation observations cover a wider range of latitudes, longitudes, and times (Lindal et al. 1981). The Voyager retrievals were based on atmospheric composition and radio refractivity data that require updating and were never properly tabulated: the few existing tabulations are incomplete and ambiguous. Here, we present a systematic electronic digitization of all available temperature profiles from Voyager, followed by their reanalysis, employing currently accepted values of the abundances and radio refractivities of atmospheric species. We find the corrected temperature at the 1 bar level to be up to 4 K greater than previously published values, i.e., 170.3{\pm}3.8 K at 12{\deg}S (Voyager 1 ingress) and 167.3{\pm}3.8 K at 0{\deg}N (Voyager 1 egress). This is to be compared with the Galileo probe value of 166.1{\pm}0.8 K at the edge of an unusual feature at 6.57{\deg}N. Altogether, this suggests that Jupiter's tropospheric temperatures may vary spatially by up to 7 K between 7{\deg}N and 12{\deg}S.