1,721,023 research outputs found
The overall configuration of the interplanetary magnetic field upstream of Saturn as revealed by Cassini observations
No full textThe Cassini spacecraft approached Saturn during the declining phase of the solar cycle, at a time when the heliosphere was highly structured by compressions and rarefactions associated with corotating interaction regions (CIRs). We examine in detail the hourly averaged interplanetary magnetic field (IMF) data prior to Saturn Orbit Insertion and during one subsequent orbit of Cassini closer to solar minimum, where the spacecraft spent several months in me solar wind. We observe the effects of CIRs on IMF structure and show examples of where this structure is disturbed by the passage of strong coronal mass ejections and by solar cycle effects. We examine the field directions and find that in general, they correspond well to the predictions of the Parker model, but with several notable deviations, which we discuss.</p
Magnetic reconnection in Saturn's magnetotail: a comprehensive magnetic field survey
No full textReconnection within planetary magnetotails is responsible for locally energizing particles and changing the magnetic topology. Its role in terms of global magnetospheric dynamics can involve changing the mass and flux content of the magnetosphere. We have identified reconnection related events in spacecraft magnetometer data recorded during Cassini's exploration of Saturn's magnetotail. The events are identified from deflections in the north-south component of the magnetic field, significant above a background level. Data were selected to provide full tail coverage, encompassing the dawn and dusk flanks as well as the deepest midnight orbits. Overall 2094 reconnection related events were identified, with an average rate of 5.0 events per day. The majority of events occur in clusters (within 3 h of other events). We examine changes in this rate in terms of local time and latitude coverage, taking seasonal effects into account. The observed reconnection rate peaks postmidnight with more infrequent but steady loss seen on the dusk flank. We estimate the mass loss from the event catalog and find it to be insufficient to balance the input from the moon Enceladus. Several reasons for this discrepancy are discussed. The reconnection X line location appears to be highly variable, though a statistical separation between events tailward and planetward of the X line is observed at a radial distance of between 20 and 30RS downtail. The small sample size at dawn prevents comprehensive statistical comparison with the dusk flank observations in terms of flux closure
Solar cycle effects on the dynamics of Jupiter's and Saturn's magnetospheres
No full textThe giant planetary magnetospheres surrounding Jupiter and Saturn respond in quite different ways, compared to Earth, to changes in upstream solar wind conditions. Spacecraft have visited Jupiter and Saturn during both solar cycle minima and maxima. In this paper we explore the large-scale structure of the interplanetary magnetic field (IMF) upstream of Saturn and Jupiter as a function of solar cycle, deduced from solar wind observations by spacecraft and from models. We show the distributions of solar wind dynamic pressure and IMF azimuthal and meridional angles over the changing solar cycle conditions, detailing how they compare to Parker predictions and to our general understanding of expected heliospheric structure at 5 and 9 AU. We explore how Jupiter's and Saturn's magnetospheric dynamics respond to varying solar wind driving over a solar cycle under varying Mach number regimes, and consider how changing dayside coupling can have a direct effect on the nightside magnetospheric response. We also address how solar UV flux variability over a solar cycle influences the plasma and neutral tori in the inner magnetospheres of Jupiter and Saturn, and estimate the solar cycle effects on internally driven magnetospheric dynamics. We conclude by commenting on the effects of the solar cycle in the release of heavy ion plasma into the heliosphere, ultimately derived from the moons of Jupiter and Saturn.</p
Statistical properties of the magnetic field in the Kronian magnetotail lobes and current sheet
No full textWe examine the characteristics of the magnetic field in Saturn's magnetotail lobes and current sheet during the Cassini spacecraft's exploration of the magnetotail from day 18 to day 291 of 2006. During this period Cassini reached maximum downtail distances of ∼68 RS, with orbits at the beginning of the survey interval concentrating on the equatorial regions, while later orbits moved to somewhat higher latitudes. We find that the field strength in the lobes falls off as Blobe (nT) = (251 ± 22) × (r (RS))−1.20±0.03. We show that the lobes and current sheet have distinctive magnetic pressure distributions, and we examine the transition of the field from the central current sheet out into the northern and southern lobes
Structure of the interplanetary magnetic field during the interval spanning the first Cassini fly-through of Saturn's magnetosphere and its implications for Saturn's magnetospheric dynamics
No full textWe examine the interplanetary magnetic field (IMF) data obtained by the Cassini spacecraft during a 5 month period spanning the first fly-through of Saturn's magnetosphere, this interval corresponding to six solar rotations at the spacecraft. It is shown that the structure of the interplanetary medium was consistent with expectations for the declining phase of the solar cycle, generally consisting of two IMF sectors and two corotating interaction region compressions during each solar rotation. Field strengths and consequent estimated reconnection voltages at Saturn's magnetopause were overall weaker by a factor of about two compared with those observed during the immediately preceding interval investigated by Jackman et al. (J. Geophys. Res., 109, A11203, doi:10.1029/2004JA010614, 2004). Specifically, during the four solar rotations immediately preceding the fly-through, it is estimated that the total open flux produced at Saturn's magnetopause was ∼60 GWb per solar rotation, compared with ∼100 GWb per solar rotation estimated similarly for the earlier interval. These values compare with estimates of ∼35 GWb of open magnetic flux typically present in Saturn's tail lobes and polar cap. However, in the solar rotation immediately following the fly-through, it is found that field and voltage values recovered to former overall values.</p
Implications of rapid planetary rotation for the Dungey magnetotail of Saturn
No full textEmploying our current understanding of the structure and dynamics of Saturn's magnetosphere, we present a time-dependent model of the kronian Dungey cycle magnetotail, which is based upon a modification of a similar model developed for Earth's magnetotail (Milan, 2004a). The major difference arises due to the rapid rotation of Saturn and the partial corotation that this imposes on the open field lines threading the polar cap. This results in twisted tail lobes, with the form of concentric cylinders of oldest to newest open flux from the inside out. The oldest, and hence longest, open field lines form the backbone of a highly extended magnetotail. Surrounding this are bundles of field lines disconnected by tail reconnection, propagating down-tail at the solar wind speed. Owing to the twisted nature of the tail, these bundles remain entangled with the lobe cores to form "exterior flux ropes." In the limit that the addition and removal of open flux from the magnetosphere by magnetic reconnection can be treated as a last-in-first-out system, we formulate a description of the flux transport within the tail and drive this with estimated dayside reconnection voltages deduced from Cassini observations of the IMF made upstream of Saturn (Jackman et al., 2004).</p
Titan's influence on Saturnian substorm occurrence
No full textSubstorms play an important role in the energization and transport of plasmas in planetary magnetospheres, including the shedding of the mass added by moons in the case of Jupiter and Saturn. Mass shedding occurs through rapid reconnection in the near tail resulting in dipolarization on the magnetospheric side of the reconnection point and plasmoid formation down tail. Observations of these sudden reconnection events in Saturn's near-tail region provide additional insight into this process. Saturnian substorms, at least on occasion, have a plasmoid formation phase leading to a traveling compression region. Changes in the field strength across reconnection events suggest that open flux has been removed fromthe tail. The timing of tail reconnection events appears to be controlled by both the orbital phase of Titan, and the variable stretching of the near-tail field as Saturn rotates.</p
Space weather in the machine learning era: A multidisciplinary approach
No full textThe workshop entitled Space Weather: A Multidisciplinary Approach took place at the Lorentz Center, University of Leiden, Netherlands, on 25-29 September 2017. The aim of this workshop was to bring together members of the Space Weather, Mathematics, Statistics, and Computer Science communities to address the use of advanced techniques such as Machine Learning, Information Theory, and Deep Learning, to better understand the Sun-Earth system and to improve space weather forecasting. Although individual efforts have been made toward this goal, the community consensus is that establishing interdisciplinary collaborations is the most promising strategy for fully utilizing the potential of these advanced techniques in solving Space Weather-related problems.</p
Reconnection events in Saturn's magnetotail: dependence of plasmoid occurrence on planetary period oscillation phase
No full textDuring its exploration of Saturn's magnetotail the Cassini magnetometer has detected many in situ examples of magnetic reconnection, in the form of plasmoids, traveling compression regions (TCRs), and dipolarizations. Meanwhile, many magnetospheric phenomena have been shown to be organized with particular regularity by planetary period oscillation systems driven separately from the Northern and Southern Hemispheres of the planet. Here we examine the relationship between the occurrence of plasmoids and TCRs and the magnetic phases of the northern and southern systems. We find a striking degree of organization of the events by both northern and southern phases, with events linked preferentially to intervals in which the magnetospheric plasma and field lines are displaced outward from the planet and the current sheet thinned, both effects being likely to favor the occurrence of reconnection and plasmoid-related mass loss. Little evidence is found for significant visibility effects associated with north-south motions of the plasma sheet
Northward field excursions in Saturn's magnetotail and their relationship to magnetospheric periodicities
Full text linkWe present results from an investigation of Cassini encounters with Saturn's magnetotail current sheet, using magnetic field and plasma data. In the first of two intervals shown, small periodic changes in the north-south component of the magnetic field are matched by periodic density enhancements associated with the plasma sheet center. In the second interval, a large plasmoid signature is observed set against a background of small-scale current sheet motions. We interpret the quasi-periodic small field deflections and density enhancements as large-scale wave-like motion of the current sheet. We stress that plasmoid signatures are of a clearly different character and occur much less frequently. Citation: Jackman, C. M., C. S. Arridge, H. J. McAndrews, M. G. Henderson, and R. J. Wilson (2009), Northward field excursions in Saturn's magnetotail and their relationship to magnetospheric periodicities, Geophys. Res. Lett., 36, L16101, doi:10.1029/2009GL039149
- …
