On the dynamics of the Jovian ionosphere and thermosphere. I. The measurement of ion winds

Abstract

We present profiles of the line-of-sight ionospheric wind velocities in the northern auroral/polar region of Jupiter. Our velocities are derived from the measurement of Doppler shifting of the H+3ν2 Q(1,0-) line at 3.953 μm. The data for this study were obtained using the facility high-resolution spectrometer CSHELL on the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, during the nights of September 7-11, 1998 (UT). A detailed analysis, allowing for several effects on the measured wavelength, is presented. The velocity profiles finally derived are consistent with an H+3 electrojet of ∼1.2 to 1.5 km s-1 flowing clockwise (as viewed from above the north rotational pole)-i.e., counter to the rotation of the planet-around the main auroral oval, for the night of September 11, and with somewhat lower velocities for September 8 and 10. In addition, we note two main regions inside (poleward of) the main auroral oval, which we call the Dark Polar Region (DPR) and the Bright Polar Region (DPR). These features correspond to the yin-yang structure noted by T. Satoh and J. E. P. Connerney (1999, Icarus 141, 236-252). The DPR appears to be strongly redshifted, with poleward winds in the line of sight up to -2.5 km s-1. The BPR may have weakly blueshifted emission. The detection of the auroral electrojet continuously over our observing run confirms the initial electrojet detection of D. Rego, N. Achilleos, T. Stallard, S. Miller, R. Prangé, M. Dougherty, and R. D. Joseph (1999, Nature 399, 121-124), as well the mechanism proposed by T. W. Hill (1979, J. Geophys. Res. 84, 6554-6558) to explain how Jupiter's equatorial magnetospheric plasmasheet is kept in corotation with the planet. We discuss the results in light of recent proposals and analyses of the jovian middle magnetosphere, and suggest that our DPR winds may be under solar wind control. © 2001 Elsevier Science (USA).