Browsing by Author "Dessler, Alexander J."
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Item 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.)Item 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.Item Origin and dynamics of the plasma sheet(1971) Hill, Thomas Westfall; Dessler, Alexander J.The plasma sheet is a region of hot (key) plasma extending several earth radii on either side of the neutral sheet in the geomagnetic tail. Its existence as a permanent feature of the magnetosphere has been well established observationally but has not been understood theoretically. A model is presented here that accounts qualitatively for both the origin and the dynamics of the plasma sheet. While several quantitative details remain to be worked out, the model can account for most of the observed features and behavior of the plasma sheet. The source of plasma-sheet particles in this model is the post-shock solar wind which injects particles into the magnetosphere principally through the demarcation lines on the magnetopause that separate closed (low-latitude) field lines from open (polar-cap) field lines. The particles drift longitudinally in pseudotrapped orbits and the higher-energy particles reach open field lines on the nightside and diffuse down the tail, forming the plasma sheet. The latitude of the demarcation lines determines the sharp high-latitude boundary of the plasma sheet, and the energy-dependent longitudinal drift accounts qualitatively for the energy spectrum of plasmasheet particles. The plasma-sheet particles escape downstream from the earth at a rate that is probably controlled by wave-particle scattering in the tail magnetic field, and drift into the neutral sheet at a rate controlled by the local cross-tail electric field. The plasma-sheet number density is governed by the balance between downstream loss and entry at the demarcation lines. When the loss rate exceeds the input rate, the resultant depletion of the near-earth plasma sheet may account for the enhanced rate of neutral-sheet merging responsible for the onset of magnetospheric substorms.Item Possible power sources for the Jovian polar infrared hot spots(1991) Zhan, Jie; Dessler, Alexander J.Strong 8-$\mu$m infrared hot spots in the polar regions of Jupiter exhibit different behaviors: the northern polar hot spot (hereafter, NPHS) tends to remain fixed in System III longitude while the southern polar hot spot (SPHS) drifts. Joule heating associated with Pedersen currents that are generated by the spinning magnetized ionosphere (the Faraday disc dynamo) is proposed as a possible power source for the hot spots. A quantitative perturbation model is used to show that the NPHS is confined by a steep longitudinal magnetic-field gradient to a System III longitude of approximately 175$\sp\circ$, in agreement with observations. The model also shows that a Joule heating power of about $10\sp{14}$-$10\sp{15}$ Watts can be dissipated in the hydrocarbon layer, significantly larger than particle-precipitation power and the radiated power of the hot spots. The drift of the SPHS is hypothesized as being caused by gravity waves. The total energy provided by Joule heating and by the dissipation of the waves constitutes the power for the hot spot; propagation of the waves causes the location of the total energy deposition to move, thus causing the drift of the SPHS. Because of the asymmetry in the polar magnetic field configurations between the two hemispheres, these gravity waves are more likely to deposit energy comparable to the Joule heating energy in the south to heat up the hydrocarbon layer where IR emission originates. The ranges of wavelength and frequency are investigated for waves that propagate mainly in north-south direction. These waves can cause the SPHS to drift at the observed speed of $\sim$5km/s and dissipate heat that is comparable to Joule heating in the south but less important than the Joule heating in the north. The current-driven joule-heating model, with the presence of wave modulation, can thus account for the primary features of the Jovian polar hot spots: their power output, the fixed location of the NPHS, and the drift motion of the SPHS.Item Relation between the magnetic moments associated with the first and third adiabatic invariants(1988) Zahn, Jonathan Clifford; Dessler, Alexander J.The motion of a charged particle in a multipole magnetic field has three adiabatic invariants associated with it. The first is that the magnetic flux through the particle's cyclotron orbit about a field line is constant. An equivalent statement is that the magnetic moment of the particle due to its cyclotron motion is constant. The second adiabatic invariant states that the integral of the particle's parallel momentum between its two mirror points is constant. The third adiabatic invariant says that the magnetic flux through a surface connected to the longitudinal invariant surface and passing through the magnetic axis is constant. In this thesis I have examined the relationship between the magnetic moments from the first and third invariants. For a particle in the equatorial plane of a dipole field, the ratio of the magnetic moment from the third invariant to that from the first invariant is 3/2.Item The lunar period, the solar period and Kp(1966) Rassbach, Michael Eric; Dessler, Alexander J.Item The stability analysis of the helical hydromagnetic waves in the tail magnetopause (Magnetopause)(1989) Zhan, Jie; Dessler, Alexander J.The interaction between the solar wind and a rotating planet causes the field lines in the planetary magnetotail to twist into a helix. Using a simplified magnetotail model, we examine hydromagnetic waves propagating down the magnetopause for such a field configuration and derive the dispersion relation of the waves. It turns out that only under certain special circumstances can the hydromagnetic waves be stable. In a thin magnetopause boundary layer, the helical wave is found to be always stable and its wave frequency depends weakly on the plasma and the field within the layer. The current system of the boundary layer is found to be modulated by the wave and the modulation is proportional to the velocity perturbation of the plasma. The wave influence on the spiral angle is examined briefly for some special cases for which we find the variation of the angle increases monotonically with increasing radial distance.