| Vol. 27, Issue 3 |
Radio emissions have long been observed from the Jovian magnetosphere. Reiner et al. [297] report that during the inbound phase of the Ulysses spacecraft's encounter with Jupiter, two types of emissions?broad-band kilometric radiation (bKOM) and narrow-band kilometric radiation (nKOM)?appear to be controlled by solar wind structures. Brightenings in the Jovian bKOM emission, followed by their sudden cessation and the onset of nKOM, are seen to recur with a 25-day period consistent with observed structures or sector boundaries within the solar wind. The actual process within the Jovian magnetosphere responsible for the modulation of the radio emissions has still to be determined. Until now, nighttime auroral images provided most of our information about the ionosphere and the magnetosphere. Rees et al. [313] have for the first time obtained a near-daytime image from the ground with the help of an imaging optical spectrometer. By taking a sequence of images in Sweden around sunset, the authors construct a two-dimensional image of the sky at 630 nm wavelength. They identify a prominent and extended bright feature between the geographic north and west, and note that its location, shape and orientation are consistent with an auroral arc, the occurrence of which at the time was independently confirmed by the POLAR spacecraft. The authors anticipate that with improvements in technique it will be possible in future to study the ionosphere and magnetosphere under all solar illumination conditions. |
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