A long-term study of Jupiter's equatorial atmosphere at the upper troposphere-lower stratosphere

Regardless of the differences among Earth, Jupiter and Saturn, several resembling phenomena occur in the atmospheres of these planets. One of the most striking is the oscillation in temperature and winds that occurs in their equatorial stratospheres on multi-year time-scales [1-3]. Decades of observations of Jupiter in the thermal IR, have shown that Jupiter’s Equatorial Stratosphere present an oscillation in temperatures between the North and South Equatorial Belts at pressure levels of 0.1-40 mbar. The vertical extension of this Jupiter Equatorial Stratospheric Oscillation (JESO) is not well determined, since retrieving temperatures above or below those levels becomes more difficult. Existing observations also suggest that the stratospheric oscillation might be affected by large convective outbreaks developing in the troposphere outside the equator and disrupting its stability [4]. The JESO is unrelated to seasons, with a variable period of 3.9-5.7 years, and numerical simulations indicate that gravity waves propagating from the troposphere are a key element of the stratospheric oscillations [5-6]. The oscillation in Saturn’s equatorial atmosphere, however, is likely related to seasonal effects with 15-year period [7].

The Cassini mission obtained observations of Saturn that showed the presence of a narrow equatorial jet located at the stratospheric hazes [8]. Recent observations of Jupiter, made by the James Webb Space Telescope (JWST), discovered an intense narrow equatorial jet located at the lower stratosphere (50-200 mbar) that has been suggested to be a deep counterpart of the JESO phenomena [9]. Additionally, recent studies in thermal infrared observations suggested that JESO might extend down to 300 mbar [10-11], thus linking the troposphere and stratosphere activity. This occurs precisely at the equator, a region where Coriolis forces vanish, complicating the usual relation between temperatures and winds that governs most dynamical aspects of the atmosphere in rapidly rotating planets.

Here we use observations taken by the Hubble Space Telescope (HST) between 2015 and 2024 at the strong methane absorption band at 890nm (FQ889N) to analyse potential temporal variations of the zonal winds and reflectivity at the equatorial latitudes. These images probe the elevated hazes at the upper troposphere (200-300 mbar), just below the narrow-elevated jet observed by JWST [9]. We present an analysis of the zonal winds over time, comparing these new winds in the methane band with previous results from Cassini [12] and JWST [9]. We investigate the potential variability of the equatorial jets in the upper troposphere and its possible relation to the lowest levels of the JESO. We also characterize the evolution of the equatorial hazes’ brightness over the same time period, which enables us to search for common trends and periodic activity. The results of this multi-year study will be presented with the goal to better understand the troposphere-stratosphere connection.

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