Modeling the compressibility of Saturn's magnetosphere in response to internal and external influences. Issue 2 (6th February 2017)

• Record Type: Journal Article
• Authors: Sorba, A. M.; Achilleos, N. A.; Guio, P.; Arridge, C. S.; Pilkington, N. M.; Masters, A.; Sergis, N.; Coates, A. J.; Dougherty, M. K.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 2(2017)
• Page Start: 1572
• Page End: 1589
• Publication Date: 2017-02-06
• Subjects: Saturn's magnetosphere -- magnetopause -- compressibility -- solar wind -- hot plasma; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2016JA023544
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: The location of a planetary magnetopause is principally determined by the balance between solar wind dynamic pressure D P and magnetic and plasma pressures inside the magnetopause boundary. Previous empirical studies assumed that Saturn's magnetopause standoff distance varies as D P − 1 / α and measured a constant compressibility parameter α corresponding to behavior intermediate between a vacuum dipole appropriate for Earth ( α ≈6) and a more easily compressible case appropriate for Jupiter ( α ≈4). In this study we employ a 2‐D force balance model of Saturn's magnetosphere to investigate magnetospheric compressibility in response to changes in D P and global hot plasma content. For hot plasma levels compatible with Saturn observations, we model the magnetosphere at a range of standoff distances and estimate the corresponding D P values by assuming pressure balance across the magnetopause boundary. We find that for "average" hot plasma levels, our estimates of α are not constant with D P but vary from ∼4.8 for high D P conditions, when the magnetosphere is compressed (≤25 R S ), to ∼3.5 for low D P conditions. This corresponds to the magnetosphere becoming more easily compressible as it expands. We find that the global hot plasma content influences magnetospheric compressibility even at fixed D P, with α estimates ranging from ∼5.4 to ∼3.3 across the range of our parameterized hot plasma content. We suggest that this behavior is predominantly driven by reconfiguration of the magnetospheric magnetic field into a more disk‐like structure under such conditions. In a broader context, the compressibility of the magnetopause reveals information about global stress balance in the magnetosphere. Key Points: A 2‐D force balance magnetodisk model is used to investigate the compressibility of Saturn's magnetosphere We find that the magnetosphere is more compressible in low solar wind conditions, due to formation of disk‐like magnetic field structure We find that the magnetosphere is also more compressible when hot plasma content is greater, due to change in magnetosphere morphology