University of Leicester
Browse

Planetary period modulations of Saturn's magnetotail current sheet during northern spring: Observations and modeling

Download (6.13 MB)
journal contribution
posted on 2017-06-21, 14:51 authored by S. W. H. Cowley, G. Provan
We study Cassini magnetic field observations at Saturn on a sequence of passes through the near-equatorial magnetotail during 2015, focusing on dual modulation of the plasma/current sheet associated with northern and southern planetary period oscillations (PPOs). Previous study of inner magnetosphere PPOs during this northern spring interval showed that the southern system amplitude was generally half that of the northern during the first part of the year to late August, after which the southern amplitude weakened to less than one-fifth that of the northern. We examine four sequential tail passes in the earlier interval, during which prominent PPO-related tail field modulations were observed, with relative (beat) phases of the two PPO systems being near in phase, antiphase, and two opposite near-quadrature conditions. We find that the radial field displayed opposite "sawtooth" asymmetry modulations under opposite near-quadrature conditions, related to previous findings under equinoctial conditions with near-equal northern and southern PPO amplitudes, while modulations were near symmetric for in-phase and antiphase conditions, but with larger radial field modulations for in-phase and larger colatitudinal field modulations for antiphase. A simple physical mathematical model of dual modulation is developed, which provides reasonable correspondence with these data using one set of current sheet parameters while varying only the relative PPO phases, thus demonstrating that dual modulation can be discerned and modeled even when the northern and southern amplitudes differ by a factor of ~ 2. No such effects were consistently discerned during the later interval when the amplitude ratio was >5.

Funding

Funded by RCUK | Science and Technology Facilities Council (STFC). Grant Number: ST/N000749/1 STFC Consolidated. Grant Number: ST/N000749/1

History

Citation

Journal of Geophysical Research: Space Physics, 2017,122

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

  • VoR (Version of Record)

Published in

Journal of Geophysical Research: Space Physics

Publisher

American Geophysical Union (AGU), Wiley

issn

2169-9380

eissn

2169-9402

Acceptance date

2017-05-23

Copyright date

2017

Available date

2017-06-21

Publisher version

http://onlinelibrary.wiley.com/doi/10.1002/2017JA023993/abstract

Notes

Calibrated magnetic field data from the Cassini mission are available from the NASA Planetary Data System at the Jet Propulsion Laboratory (https:// pds.jpl.nasa.gov/).

Language

en

Usage metrics

    University of Leicester Publications

    Categories

    No categories selected

    Keywords

    Licence

    Exports

    RefWorks
    BibTeX
    Ref. manager
    Endnote
    DataCite
    NLM
    DC