Propagation of a quasi-stationary zonal wavenumber-2 Rossby wave in Jupiter's stratosphere

Atmospheric planetary waves redistribute energy and momentum and shape the large-scale circulation of giant-planet atmospheres. However, the three-dimensional structure and dynamical role of low-zonal-wavenumber waves on Jupiter remain poorly constrained. We investigate the structure, propagation, and possible dynamical influence of a low-zonal-wavenumber wave in Jupiter's upper troposphere and stratosphere, with a particular emphasis on its coupling to the quasi-quadrennial oscillation (QQO). We analysed four global temperature maps retrieved from Cassini Composite Infrared Spectrometer (CIRS) observations obtained during the 2000--2001 Jupiter flyby. The zonal wavenumber-2 temperature disturbance was isolated from the retrieved three-dimensional temperature field and diagnosed using vertical phase structure, refractive-index calculations, and Eliassen--Palm flux diagnostics. We identify a coherent zonal wavenumber-2 temperature disturbance in Jupiter's northern mid-latitudes that maintains a nearly fixed longitudinal phase over multiple observing epochs, indicating a quasi-stationary Rossby wave. Its vertical phase tilt demonstrates upward propagation, while refractive-index diagnostics show confinement within a favourable westerly waveguide. Eliassen--Palm flux diagnostics further show upward propagation followed by poleward refraction near the turning line associated with the easterly phase of the QQO. Regions of EP-flux convergence indicate momentum deposition into the background flow and suggest that the wave may in turn influence the evolution of the QQO. These results provide observational constraints on the dynamical coupling between planetary Rossby waves and Jupiter's QQO, with broader implications for understanding wave--mean-flow interactions in planetary atmospheres exhibiting quasi-periodic oscillations.