Abstract. For the sets of magnetic clo•ds studied in this workwe have shown the existence of a relationship between their peak magnetic field strength and peak velocity values, with a clear tendency that, clouds which move at, higher speeds also possess higher core magnetic field strengths. This result suggests a possible intrinsic property of magnetic clouds and also implies a geophysical consequence. The relatively low field strengths at low velocities is pres•mably the cause of the lack of intense storms during low speed e. jecta. There is also an indication that, this type of behavior is peculiar for magnetic clouds, whereas other types of non cloud-driver gas events do not, seem to show a similar relationship, at least, for the data studied in this paper. We suggest that, a field/speed relationship for magnetic clouds, as that obtained in our present study, could be associated with the cloud release and acceleration mechanism a.t the sun.Since for magnetic clouds the total field tyically has a substantial southward component, B•, our results in,ply that the interplanetary dawn-dusk electric field, given by v x Bs (where v is the cloud's velocity), is enhanced by both factors. Therefore, the consequent magnetospheric energization (that is governed by this electric field) becomes more efficient for the occurrence of magnetic storms.
Abstract.One of the interesting observations from the FAST satellite is the detection of strong spiky waveforms in the parallel electric field in association with ion cyclotron oscillations in the perpendicular electric fields. We report here an analytical model of the coupled nonlinear ion cyclotron and ion-acoustic waves, which could explain the observations. Using the fluid equations for the plasma consisting of warm electrons and cold ions, a nonlinear wave equation is derived in the rest frame of the propagating wave for any direction of propagation oblique to the ambient magnetic field. The equilibrium bulk flow of ions is also included in the model to mimic the field-aligned current. Depending on the wave Mach number M defined by M = V /C s with V and C s being the wave phase velocity and ion-acoustic speed, respectively, we find a range of solutions varying from a sinusoidal wave form for small amplitudes and low M to sawtooth and highly spiky waveforms for nearly parallel propagation. The results from the model are compared with the satellite observations.
Abstract. We show evidence for mirror mode structures at comet Giacobini-Zinner. These are plasma structures with alternating high ß and low ß regions driven unstable when ß<perp> /ß<parallel> > 1+ 1/<perp>. These structures are detected in a region just adjacent to the magnetic tail and have scale sizes of ≈ 12 H2O group ion cyclotron radii. Calculations are presented to show that mirror mode instability can occur due to the perpendicular pressure associated with H2O+ cometary pickup ions in the region of mirror mode observation. Adjacent regions (in the magnetic tail and further in the sheath) are found to be stable to the mirror mode. Plasma waves are detected in relation with the mirror mode structures. Low frequency 56 to 100 Hz waves are present in the high beta portions, and high frequency, 311 Hz to 10 kHz, waves are present in low beta regions. These may be electromagnetic lion roar waves and electrostatic festoon-shaped waves, respectively, in analogy to plasma waves detected in the Earth's magnetosheath.
Abstract. We present here a systematic simulational study on electron beam driven waves and their consequences in terms of plasma electrodynamics. The study is performed by using three-dimensional particle-in-cell code, parallelized to simulate a large volume of plasma. Our simulation shows that an initial electron beam of finite radius with beam velocity along the ambient magnetic field triggers a series of events in the evolution of the waves and the plasma.
The nonlinear evolution of low-frequency electrostatic oscillations in a magnetized plasma consisting of protons, electrons and oxygen ion beams has been studied. The fluid equations have been used for the oxygen beam, whereas the Boltzmann distributions are used for the protons and electrons. The coupled system of equations are reduced to a single nonlinear differential equation in the rest frame of the propagating wave for any direction of propagation with respect to the ambient magnetic field. This nonlinear differential equation is solved numerically for the parameters charateristic of the auroral acceleration region. Depending on the wave Mach number, proton and oxygen ion concentrations, and driving electric field, the numerical solutions show a range of periodic solutions varying from sinusoidal to sawtooth and highly spiky waveforms. The effects of the plasma parameters, in particular the oxygen ion concentration and the proton temperature on the evolution of the nonlinear waves are examined. The results from the model are compared with satellite observations.
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