Showing papers by "Peter A. Delamere published in 2006"

Io‐Jupiter interaction: Alfvén wave propagation and ionospheric Alfvén resonator

Abstract: [1] A linear, one-dimensional gyrofluid code has been used to determine the characteristics of propagating Alfven waves and the ionospheric Alfven resonator on a Jupiter-Io flux tube. This model includes electron inertia, electron pressure gradient, and finite ion gyroradius effects, as well as the displacement current correction to prevent the Alfven velocity from exceeding the speed of light. A quasi-steady Vlasov code provides realistic density profiles along the flux tube as input parameters for the gyrofluid model. In this paper, we demonstrate that the majority of the wave energy from an initial pulse with a long wavelength (∼0.1 RJ) is unable to reach Jupiter's ionosphere without wave breaking, phase mixing, and/or other nonlinear processes; however, a significant energy flux may be transferred via high-frequency, small-wavelength waves to the ionosphere. The waves that reach the ionosphere stimulate an ionospheric Alfven resonator which is generated between the ionospheric boundary and the first velocity peak of the Alfven phase speed. The ionospheric density and scale height play important roles to determine the resonant frequency. The eigenfrequency decreases with increasing scale height and with increasing ionospheric density. The fundamental frequency and higher harmonics of the Alfven resonator are comparable to the observed reoccurring frequency of S bursts between a few and hundreds of Hz. On the basis of this information, we suggest the Alfven resonator as the likely driver explaining multiple occurrences of S bursts.

Hybrid code simulations of the solar wind interaction with Comet 19P/Borrelly

Abstract: [1] Detailed observations of the plasma environment of Comet 19P/Borrelly were made by the Plasma Experiment for Planetary Exploration (PEPE) during the Deep Space 1 (DS1) flyby on 22 September 2001. DS1 flew from north to south relative to the plane of the ecliptic on the sunward side of the comet and all plasma boundaries (i.e., first and last pickup ions, bow shock, decelerated solar wind) were observed to be shifted northward. This surprising result was initially attributed to large well-collimated dayside jets directed ∼10° northward from the nucleus as observed by the DS1 MICAS camera. However, ground-based observations of Schleicher et al. (2003) indicate a symmetric gas cloud with respect to the comet-Sun line. In an attempt to resolve this conundrum, we have conducted a series of hybrid plasma simulations to investigate the effects of the large pickup ion gyroradius (i.e., comparable to the length scale of the cometary obstacle) at 1.36 AU. We find that that a maximum asymmetry, consistent with the observations, is generated when the pickup ion gyroradius is comparable to or less than the standoff distance of the bow shock (BIMF ∼ 4 nT). The degree of asymmetry is reduced for larger and smaller magnetic field strengths.