Browsing by Author "Yang, Yong-Shiang"

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    Is System IV a sideband of System III? The periodogram analyses of EUV and nKOM data
    (1989) Yang, Yong-Shiang; Dessler, Alexander J.
    Jupiter's magnetosphere does not rigidly rotate with the System III angular rate. There is a corotation lag as a function of distance in the Jovian magnetosphere. The dominant rotational component, aside from System III, is a 3% longer period (System IV). System IV could be interpreted as a sideband of System III being amplitude-modulated by the 14.1-day period. Whether System IV is an independent Jovian coordinate or just a sideband is investigated in this thesis. The 9.64 hour period does not appear in periodogram analyses of EUV data from Voyager 2 and nKOM data from Voyager 1 and 2. Therefore, it is concluded that System IV is not a sideband and it is independent of System III. Through harmonic filtering, a signal with a 12.5-day period in the EUV data is found. It is suggested that the 12.5-day period is a solar-wind effect. (Abstract shortened with permission of autor.)
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    Numerical simulation of the Jovian torus-driven plasma transport
    (1992) Yang, Yong-Shiang; Dessler, Alexander J.
    The Rice Convection Model has been modified and applied to the study of the Jovian magnetospheric system, which is interchange unstable. The basic interchange instability of the Io plasma torus is opposed by pressure gradients in the energetic particles outside the torus. Many simulations have been performed for cases where the overall system is inter-change unstable under the ideal-MHD assumption E + v $\times$ B = 0. For such cases, the torus breaks up predominantly into long fingers unless the initial condition strongly favors some other mode. The ends of the fingers tend to be rounded, and they are connected to the main torus by tails that thin rapidly with time if the torus runs out of plasma. Our calculations place an upper limit of $\sim$1R$\sb{\rm J}$ on the average distance between fingers. For an initially asymmetric large-scale torus, fingers generally form on a time scale shorter than the one on which the heavy side of the torus falls outwards. However, the fingers form predominantly on the heavy side. Galileo may observe such finger features outside the Io torus, at L $\approx$ 7 to 15._x000D_ Additionally, in this thesis, drift-wave theory has been used to investigate the effect of energetic (KeV or MeV) particles on the Io torus plasma transport. It is shown that the MHD stability criterion, where the interchange motion would be completely stabilized if the energy density of the hot stabilizing plasma is greater than or dual to 3/4 of that of the cold unstable plasma, no longer holds owing to the gradient/curvature drift of the energetic particles. This differential-drift effect, which is a departure from the ideal-MHD and frozen-in flux, may play a significant role in plasma transport in the Jovian magnetosphere.