Multispacecraft observations of Jovian DAM.

Planetary magnetospheres, in particular the Jovian magnetosphere, provide the conditions of a complex source of powerful coherent non-thermal radio emissions attributed to the mechanism of the cyclotron maser instability. This emission is a result of a complicated interaction between the exceptionally dynamic Jovian magnetosphere and energetic particles supplying the free energy from planetary rotation and the interaction between Jupiter and the Galilean moons. Thus, auroral radio emission can be regarded as a very good tool to survey the energy dissipation in the auroral zones as well as to remotely monitor the activity and dynamics of the Jovian magnetosphere. Main subject of the proposed research project is the Jovian decametric radio emission (DAM) - the strongest component of the auroral radio emission of Jupiter. The research program consists of two main parts. The first one is the investigation of the new type of periodic radio bursts in the non-Io component of Jovian DAM. These periodic bursts, recently discovered by our research group (IWF Graz) in radio spectra, recorded by several spaceborn radio experiments, are characterized by a very periodical reoccurrence during several Jupiter`s days with a period ~1.5% longer than the rotation rate of the Jovian magnetosphere. Most probably this phenomenon is deeply connected with the complex interaction between the Jovian magnetosphere and sub-corotating highly structured plasma environment. Besides of the general scientific value, a full understanding of the nature of the periodic bursts may shed some light on the physics of the global plasma dynamics in the Jovian magnetosphere and its interaction with the solar wind. The second main part of the proposal is the investigation of the beaming properties of the Io controlled DAM. The use of the multispacecraft stereoscopic observations of the Jovian DAM is a very promising approach in the field of planetary magnetospheric radio physics. Both parts of the proposed research program include the analysis of the available observational data, development of theoretical models and physical scenarios for the interpretation of the observed phenomena. Based on an extensive international scientific collaboration with the leading planetary magnetospheric physics research groups the proposed project is of high actuality in view of future space missions to Jupiter, such as the NASA mission JUNO and joint NASA-ESA Europa Jupiter System Mission (EJSM).

The magnetosphere of Jupiter is a complex source of a powerful radio emission which is a product of complicated interactions between the Jovian magnetosphere and energetic particles supplied by the free energy from the planetary rotation and the interaction between Jupiter and Galilean moons. The FWF project P23762-N16 Multispacecraft observations of Jovian DAM deals with the non-thermal decametric radio emission (DAM) which is the strongest component of Jupiters radiation. The main objectives of the project have been reached by studies on a new type of periodic decametric radio bursts and on the beaming properties of DAM using simultaneous observations from radio instruments on-board spacecraft and from ground-based radio telescopes. The main properties of the periodic radio bursts of DAM have been studied, which are characterized by a period which is 1.5% longer than the rotation of the Jovian magnetosphere. We have investigated the relations between the periodic bursts and the solar wind as well as the activity of the auroral region of Jupiter. A mechanism of the periodic bursts generation has been proposed. The performed analysis of the stereoscopic spacecraft observation of the DAM radio emission yields estimates of characteristics of the beaming properties of the DAM, controlled by the moon Io, such as the thickness of the emission cone. We also organized, together with international observer teams cooperating with this project, a long-lasting campaign of Jupiter observations using the large ground-based decametric radio telescopes. In the course of the analysis of the radio data we have discovered a new type of zebra-like striped narrowband structures in DAM which have never been reported before in this frequency range.