Journal article
Solar Energetic Particles (SEP) and Galactic Cosmic Rays (GCR) as tracers of solar wind conditions near Saturn: Event lists and applications
Icarus (New York, N.Y. 1962), Vol.300, pp.47-71
01/15/2018
DOI: 10.1016/j.icarus.2017.08.040
Abstract
•Energetic particles used for non-stop monitoring of solar wind transients at Saturn.•63 intervals of CME and CIRs impacting Saturn identified between 2004 and 2016.•Solar-wind induced dynamics in Saturn’s electron radiation belts are now resolved.•A strong magnetospheric compression at Saturn has also been linked to a CME event.•Numerous options to study Saturn’s magnetospheric response to the solar wind.
The lack of an upstream solar wind monitor poses a major challenge to any study that investigates the influence of the solar wind on the configuration and the dynamics of Saturn’s magnetosphere. Here we show how Cassini MIMI/LEMMS observations of Solar Energetic Particle (SEP) and Galactic Cosmic Ray (GCR) transients, that are both linked to energetic processes in the heliosphere such us Interplanetary Coronal Mass Ejections (ICMEs) and Corotating Interaction Regions (CIRs), can be used to trace enhanced solar wind conditions at Saturn’s distance. SEP protons can be easily distinguished from magnetospheric ions, particularly at the MeV energy range. Many SEPs are also accompanied by strong GCR Forbush Decreases. GCRs are detectable as a low count-rate noise signal in a large number of LEMMS channels. As SEPs and GCRs can easily penetrate into the outer and middle magnetosphere, they can be monitored continuously, even when Cassini is not situated in the solar wind. A survey of the MIMI/LEMMS dataset between 2004 and 2016 resulted in the identification of 46 SEP events. Most events last more than two weeks and have their lowest occurrence rate around the extended solar minimum between 2008 and 2010, suggesting that they are associated to ICMEs rather than CIRs, which are the main source of activity during the declining phase and the minimum of the solar cycle. We also list of 17 time periods ( > 50 days each) where GCRs show a clear solar periodicity ( ∼ 13 or 26 days). The 13-day period that derives from two CIRs per solar rotation dominates over the 26-day period in only one of the 17 cases catalogued. This interval belongs to the second half of 2008 when expansions of Saturn’s electron radiation belts were previously reported to show a similar periodicity. That observation not only links the variability of Saturn’s electron belts to solar wind processes, but also indicates that the source of the observed periodicity in GCRs may be local. In this case GCR measurements can be used to provide the phase of CIRs at Saturn. We further demonstrate the utility of our survey results by determining that: (a) Magnetospheric convection induced by solar wind disturbances associated with SEPs is a necessary driver for the formation of transient radiation belts that were observed throughout Saturn’s magnetosphere on several occasions during 2005 and on day 105 of 2012. (b) An enhanced solar wind perturbation period that is connected to an SEP of day 332/2013 was the definite source of a strong magnetospheric compression which led to open flux loading in the magnetotail. Finally, we propose how the event lists can define the basis for single case studies or statistical investigations on how Saturn and its moons (particularly Titan) respond to extreme solar wind conditions or on the transport of SEPs and GCRs in the heliosphere.
Details
- Title: Subtitle
- Solar Energetic Particles (SEP) and Galactic Cosmic Rays (GCR) as tracers of solar wind conditions near Saturn: Event lists and applications
- Creators
- E. Roussos - Max Planck Institute for Solar System ResearchC.M. Jackman - University of SouthamptonM.F. Thomsen - Planetary Science InstituteW.S. Kurth - University of IowaS.V. Badman - Lancaster UniversityC. Paranicas - Johns Hopkins University Applied Physics LaboratoryP. Kollmann - Johns Hopkins University Applied Physics LaboratoryN. Krupp - Max Planck Institute for Solar System ResearchR. Bučík - Max Planck Institute for Solar System ResearchD.G. Mitchell - Johns Hopkins University Applied Physics LaboratoryS.M. Krimigis - Johns Hopkins University Applied Physics LaboratoryD.C. Hamilton - University of Maryland, College ParkA. Radioti - University of Liège
- Resource Type
- Journal article
- Publication Details
- Icarus (New York, N.Y. 1962), Vol.300, pp.47-71
- Publisher
- Elsevier Inc
- DOI
- 10.1016/j.icarus.2017.08.040
- ISSN
- 0019-1035
- eISSN
- 1090-2643
- Grant note
- DOI: 10.13039/100006196, name: JPL, award: 1243218; DOI: 10.13039/501100000271, name: STFC, award: ST/M005534/1; DOI: 10.13039/501100001659, name: Deutsche Forschungsgemeinschaft, award: BU 3115/2-1
- Language
- English
- Date published
- 01/15/2018
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984455269902771
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