Interaction between eddies and mean flow in Jupiterʹs atmosphere: Analysis of Cassini imaging data

Beebe et al. [Beebe, R.F., et al., 1980. Geophys. Res. Lett. 17, 1–4] and Ingersoll et al. [Ingersoll, A.P., et al., 1981. J. Geophys. Res. 86, 8733–8743] used images from Voyagers 1 and 2 to analyze the interaction between zonal winds and eddies in Jupiterʹs atmosphere. They reported a high positive correlation between Jupiterʹs eddy momentum flux, ρ u ′ v ′ ¯ , and the variation of zonal velocity with latitude, d u ¯ / d y . This correlation implied a surprisingly high rate of conversion of energy from eddies to zonal flow: ∼ 1.5 – 3.0   W m −2 , a value more than 10% of Jupiterʹs thermal flux emission. However, Sromovsky et al. [Sromovsky, L.A., et al., 1982. J. Atmos. Sci. 39, 1413–1432] argued that possible biases in the analysis could have caused an artificially high correlation. In addition, significant differences in the derived eddy flux between datasets put into question the robustness of any one result. We return to this long-standing puzzle using images of Jupiter from the Cassini flyby of December 2000. Our method is similar to previous analyses, but utilizes an automatic feature tracker instead of the human eye. The number of velocity vectors used in this analysis is over 200,000, compared to the 14,000 vectors used by Ingersoll et al. We also find a positive correlation between u ′ v ′ ¯ and d u ¯ / d y and derive a global average power per unit mass, u ′ v ′ ¯ d u ¯ / d y , ranging from ( 7.1 – 12.3 ) × 10 −5   W kg −1 . Utilizing Ingersoll et al.ʹs estimate of the mass per unit area involved in the transport, this would imply a rate of energy conversion of ∼ 0.7 – 1.2   W m −2 . We discuss the implications of this result and employ several tests to demonstrate its robustness.