Data analysis in combination with numerical simulations of the acceleration and propagation of energetic particles in the vicinity of planetary magnetospheres
Final Report Abstract
The main goals of the project can be divided into the basic topics about the magnetospheric origin of the 10h periodicity of Jovian electrons, their propagation within Jovian Jet events and the physical nature of these Jets. While the propagation issue was addressed both by observational and numerical methods, the two other topics were treated by a detailed (re-) investigation of observational data by applying new methods. The project first had the goal to re-analyze the data of energetic particle (electron) Jet events of Jovian origin. These Jets events are characterized by sharp increases and decreases of the counting rates, a plateau-like behavior of not more than a few hours, a strong anisotropy along the magnetic field, their spectral shape as well as by the 10h modulation of the latter, which reflects the planet's fast rotation. To go to the bottom of the question of the origin of this Jovian “clock”, we did not only investigate interplanetary measurements of the Ulysses and Pioneer 10/11 spacecraft, but also MeV-electron measurements during the flybys of these spacecraft in the Jovian magnetosphere. Magnetospheric origin: The 10 h periodicity of the Jovian electron spectrum in the magnetosphere is extensively discussed in the literature. Three models - the disc, anomaly and clock models - where developed, among which the clock model is the generally accepted one. It predicts that the behavior is only a function of time, but not of position. Due to the application of statistical and time series analysis methods we could, however, identify for the first time another quasi-periodic variation of the energy spectrum that is closely correlated with Jupiter’s current sheet as well as the high-latitude boundary layer that could be clearly seen during the inbound and outbound passes of Ulysses, respectively. Propagation: A characteristic feature of Jovian Jet electrons is the fact that they carry the 10 h periodicity of the magnetosphere in connection with a strong directional anisotropy. Ferrando et al. (1993) investigated these two quantities and showed by means of phase histograms that the periodicity vanishes beyond ~0.8AU away from the planet. Dunzlaff (2013) developed a numerical model that solves Roelof's pitch-angle dependent transport equation (Roelof, 1969) in magnetic flux tubes. The main finding was that the 10h periodicity does not vanish, so that Dunzlaff et al. (2013) applied new spectral analysis methods and actually discovered the 10 h periodicity in several additional events at ~1.2 AU, with strong hints for the existence of flux tubes carrying these signals possibly even up to ~2.2 AU away from the planet. In contrast to the model expectation, not all anisotropic events were accompanied by the spectral variation. On the one hand, this may be due to the short duration of the events that does not allow to detect a periodicity of 10h, on the other hand, the re-analysis of large bursts of Jovian electron that carry the 10 h modulation observed by Pioneer 10 revealed that these bursts are a composition of Jovian Jet events that include “long-lasting” periods of time with small but significant anisotropies. This fact suggests a correlation between the interplanetary conditions the Jets are embedded into and the detectability of the 10 h modulation. Such an effect has actually been found for the Ulysses events. Nature of Jovian Jets: Jovian Jets are thought to be generated via reconnection of the heliospheric magnetic field with the Jovian magnetosphere. The majority of events, however, require large deviations from the nominal Parker spiral in order to be connected to the observer. Thus, Dunzlaff et al. (2010) investigated the electron, plasma and magnetic field data and could demonstrate that (i) individual magnetic flux tubes, i.e. bundles of magnetic field lines, can be found even at the orbit of Jupiter and in the regions over the poles of the Sun, extending the findings by Borovsky (2008) at 1 AU further out into the heliosphere, (ii) the occurrence of Jovian jets are the result of the interaction of these magnetic flux tubes with the Jovian magnetosphere, and (iii) the nature of Jovian electron jets can be explained in terms of these flux tubes that allow particles to travel over large distances across the mean magnetic field without a rapid spread of particles as expected by a simple field line random walk.
Publications
-
Comparison of Jovian jets observed by Ulysses and Pioneer 10”, presented at the International Cosmic Ray Conference, 2009
P. Dunzlaff, A. Kopp, B. Heber, and O. Sternal
-
“Propagation of Jovian electron jets in heliospheric flux tube structures”, Journal of Geophysical Research, vol. 115, A10106, 2010
P. Dunzlaff, A. Kopp, and B. Heber
-
“Analysis of Anisotropic Jovian Electron Events”, doctoral thesis, Christian- Albrechts-Universität zu Kiel, Kiel, 2013
P. Dunzlaff
-
”Ulysses observations of Jupiter's 10 h modulation in interplanetary space in 2004”, Journal of Geophysical Research, 118, 4021-4032, 2013
P. Dunzlaff, B. Heber and A. Kopp
