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Differentially rotating plasma disks, around compact objects, that are imbedded in a ``seed'' magnetic field are shown to develop vertically localized ballooning modes that are driven by the combined radial gradient of the rotation frequency and vertical gradients of the plasma density and temperature. When the electron mean free path is shorter than the disk height and the relevant thermal conductivity can be neglected, the vertical particle flows produced by of these modes have the effect to drive the density and temperature profiles toward the ``adiabatic condition'' where $\eta_{T}\equiv(dlnT/dz)/(dlnn/dz)=2/3$. Here $T$ is the plasma temperature and $n$ the particle density. The faster growth rates correspond to steeper temperature profiles $(\eta_{T}>2/3)$ such as those produced by an internal (e.g., viscous) heating process. In the end, ballooning modes excited for various values of $\eta_{T}$ can lead to the evolution of the disk into a different current carrying configuration such as a sequence of plasma rings.

A dynamical analysis is presented that self-consistently takes into account the motion of the critical layer, in which the magnetic field reconnects, to describe how the m=n=1 resistive internal kink mode develops in the nonlinear regime. The amplitude threshold marking the onset of strong nonlinearities due to a balance between convective and mode coupling terms is identified. We predict quantitatively the early nonlinear growth rate of the m=n=1 mode below this threshold.

A series of plasma voids ('dropouts') was observed by the Plasma Science (PLS) experiment in Jupiter's magnetosphere during the Voyager 2 encounter with that planet. A reexamination of Voyager 2 data has led to the conclusion that the dropout phenomenon cannot be a manifestation of a plasma wake produced by Ganymede. Rather, the appearance of the dropouts is attributed to changes in the upstream solar wind conditions and the global state of the magnetosphere; the proximity of Voyager 2 to Ganymede at the time is considered to be coincidental. It is suggested that these dropouts are evidence of a state of 'bubbling' of the magnetosphere that alternates with 'laminar' states in which, as in the case of the Voyager 1 encounter with Jupiter, voids are not present and that these states correspond to different processes by which plasma is transported out of the system. The nature of these states is related to changes in the magnitude of the upstream solar wind ram pressure. In the bubbling state, this pressure is higher than in the laminar state and drives an intermittent instability. The analysis presented is one of the first attempts to introduce, in space physics, recently acquired theoretical notions of the physics of the finite-beta plasmas of which the Jovian magnetospheric plasma is an important example.