A search for p-mode oscillations of Jupiter - Serendipitous observations of nonacoustic thermal wave structure

Abstract

We have computed frequencies for p-mode oscillations of Jupiter and have used a sensitive observational technique to search for the modes. Because of the long radiative damping time, Jovian p-modes will be more adiabatic than in the solar case, and infrared brightness temperature fluctuations represent a sensitive method for their detection. We observed the infrared intensity of the Jovian disk in a broad bandwidth (8-13 /mi), using a 20 element linear array. Our measurements were made as a function of longitude, giving maximum sensitivity for sectoral modes, at 20° N and at the equator. No p-mode oscillations were seen at the ~0.07 K level in 8-13 /mi brightness temperature (equivalent to 1 m s-1 in velocity). Applying the Goldreich and Kumar theory for the equilibrium of acoustic energy with turbulence, we conclude that Jovian p-modes are not likely to have observable amplitudes. Our observations are consistent with the theoretical expectation that other modes of oscillation, such as occur under the influence of a strong Coriolis force, may provide more useful probes of the Jovian interior. Our data serendipitously reveal the existence of a prominent, nonacous-tic, wavelike structure in the 8-13 /mi brightness temperature, which occurs both at 20° N and at the equator. This structure was unchanged over two Jovian rotations, implying a very low frequency for the wave. This thermal wave structure is similar in amplitude and spatial scale to the slowly moving thermal features recently discovered in the Voyager IRIS data by Magalhäes et al, and which these authors attribute to a "deeply-rooted fluid dynamical regime beneath the surface meteorology."