Magnetospheric Energetic Ion Research Articles

UV-VIS, INFRARED, AND MASS SPECTROSCOPY OF ELECTRON IRRADIATED FROZEN OXYGEN AND CARBON DIOXIDE MIXTURES WITH WATER

Ozone has been detected on the surface of Ganymede via observation of the Hartley band through the use of ultraviolet spectroscopy and is largely agreed upon to be formed by radiolytic processing via interaction of magnetospheric energetic ions and/or electrons with oxygen-bearing ices on Ganymede's surface. Interestingly, a clearly distinct band near 300 nm within the shoulder of the UV-Vis spectrum of Ganymede was also observed, but currently lacks an acceptable physical or chemical explanation. Consequently, the primary motivation behind this work was the collection of UV-Vis absorption spectroscopy of ozone formation by energetic electron bombardment of a variety of oxygen-bearing ices (oxygen, carbon dioxide, water) relevant to this moon as well as other solar system. Ozone was indeed synthesized in pure ices of molecular oxygen, carbon dioxide and a mixture of water and oxygen, in agreement with previous studies. The Hartley band of the ozone synthesized in these ice mixtures was observed in the UV-Vis spectra and compared with the spectrum of Ganymede. In addition, a solid state ozone absorption cross section of 6.0 ± 0.6 × 10{sup –17} cm{sup 2} molecule{sup –1} was obtained from the UV-Vis spectral data. Ozone was not produced in the irradiated carbon dioxide-watermore » mixtures; however, a spectrally 'red' UV continuum is observed and appears to reproduce well what is observed in a large number of icy moons such as Europa.« less

Analysis of EMIC‐wave‐moderated flux limitation of measured energetic ion spectra in multispecies magnetospheric plasmas

A differential Kennel‐Petschek (KP) flux limit for magnetospheric energetic ions is devised taking into account multiple ion species effects on electromagnetic ion cyclotron (EMIC) waves that scatter the ions. The idea is that EMIC waves may limit the highest ion intensities during acceleration phases of storms and substorms (~ hour) while other mechanisms (e.g., charge exchange) may account for losses below those limits and over longer periods of time. This approach is applied to published Earth magnetosphere energetic ion spectra (~ keV to ~1 MeV) for radial positions (L) 3 to 6.7 RE. The flatness of the most intense spectral shapes for <100 keV indicate sculpting by just such a mechanism, but modifications of traditional KP parameters are needed to account for maximum fluxes up to 5.4 times greater than expected. Future work using the new capabilities of the Van Allen Probes mission will likely resolve outstanding uncertainties.

Energetic ion spectral characteristics in the Saturnian magnetosphere using Cassini/MIMI measurements

We report sample results on Saturn magnetospheric energetic ion spectral shapes using measurements obtained from the Magnetospheric Imaging Instrument (MIMI) suite onboard Cassini. The ion intensities are measured by the Charge Energy Mass Spectrometer (CHEMS) that covers the energy range of 3 to 236 keV/e, the Low Energy Magnetospheric Measurements System (LEMMS) covering the energy range of 0.024 < E < 18 MeV, and the Ion Neutral Camera (INCA) that provides ion measurements in the ion mode at the energy range ∼5.5 to >220 keV for protons. The data used cover several passes from the period 1 July 2004 to 10 April 2007, at various latitudes over the dipole L range 5 < L < 20 RS. The spectra generally show a power law in energy form at larger L values but display a flattening/relative peak at lower (L < 10) values centered at ∼50 to ∼100 keV and can be fit by a κ distribution function with characteristic kT ranging from ∼10 to ∼100 keV. The results are consistent with the assumption that energetic protons are heated adiabatically as they move inward to stronger magnetic fields, in contrast to the singly ionized oxygen that seems to be heated locally at each L shell. The lack of any trend of the O+ temperature versus L shell implies that nonadiabatic energization mechanisms and charge exchange with Saturn's neutral gas cloud play an important role for ion energetics.

Geometrical characteristics of magnetospheric energetic ion time series: evidence for low dimensional chaos

Abstract. In the first part of the paper we study the geometrical characteristics of the magnetospheric ions’ time series in the reconstructed phase space by using the SVD extended chaotic analysis, and we test the strong null hypothesis supposing that the ions’ time series is caused by a linear stochastic process perturbed by a static nonlinear distortion. The SVD reconstructed spectrum of the ions’ signal reveals a strong component of high dimensional, external coloured noise, as well as an internal low dimensional nonlinear deterministic component. Also, the stochastic Lorenz system produced by coloured noise perturbation of the deterministic Lorenz system was used as an archetype model in comparison with the dynamics of the magnetrospheric ions.Key words. Magnetospheric physics (energetic particles) – Radio science (nonlinear phenomena)

Dynamical characteristics of magnetospheric energetic ion time series: evidence for low dimensional chaos

Abstract. This paper is a companion to the first work (Pavlos et al., 2003), which contains significant results concerning the dynamical characteristics of the magnetospheric energetic ions’ time series. The low dimensional and nonlinear deterministic characteristics of the same time series were described in Pavlos et al. (2003). In this second work we present significant results concerning the Lyapunov spectrum, the mutual information and prediction models. The dynamical characteristics of the magnetospheric ions’ signals are compared with corresponding characteristics obtained for the stochastic Lorenz system when a coloured noise perturbation is present. In addition, the null hypothesis is tested for the dynamical characteristics of the magnetospheric ions’ signal by using nonlinear surrogate data. The results of the above comparisons provide significant evidence for the existence of low dimensional chaotic dynamics underlying the energetic ions’ time series.Key words. Magnetospheric physics (energetic particles) – Radio sciences (nonlinear phenomena)

Electron‐ and photon‐stimulated desorption of K from ice surfaces

Motivated by controversy concerning the origin of alkali metal vapor in the atmosphere of the Jovian satellite Europa, we present laboratory studies of the electron‐stimulated desorption (ESD) and photon‐stimulated desorption (PSD) of atomic K deposited on the surface of thin water ice films. These ice films of both crystalline and amorphous modifications simulate the surface of icy satellites. A pulsed low‐energy electron gun and a mercury arc lamp serve as sources of electron and UV irradiation. X‐ray photoelectron spectroscopy (XPS) is used for surface chemical state control. Both ESD and PSD of potassium atoms from ice exhibit appearance thresholds at ∼4 eV, which is more pronounced for the case of crystalline ice than for amorphous ice. The velocity distribution of desorbed K atoms, measured at 100 K, is peaked at ∼500 m/s (by comparison, the peak for Na is at ∼800 m/s), with the high‐energy portion extended up to ∼3000 m/s. The mechanism of desorption is identified as an electronically excited charge transfer from ice to alkali ion, followed by desorption. We conclude that along with magnetospheric energetic ion sputtering processes, UV solar photons and electron fluxes with E > 4 eV may cause alkali metal desorption from Europa's surface.

Magnetospheric energetic ions from the Earth's ionosphere

In the decade and a half since the initial discovery that the Earth's own ionosphere could at times contribute measurably to the hot plasma in the magnetosphere we have made significant progress in both our knowledge and understanding of this connection. We now know that ions of ionospheric origin are found in all major regions of the magnetosphere and at its boundaries. The source region in the ionosphere and the acceleration and transport processes involved in coupling the cold ionospheric plasma to the hot magnetospheric plasma are complex and variable. We now have a good understanding of the large scale morphology of the ionospheric outflow and its distribution throughout the magnetosphere and progress is being made in the understanding of the fundamental physical processes involved. In this paper we concentrate on the large scale morphology and our understanding of the sources for ionospheric ions found in various regions of the magnetosphere and their transport.