Dependence of Thermodynamic Processes on Upstream Interplanetary Magnetic Field Conditions for Magnetosheath Ions. Issue 3 (28th March 2019)

• Record Type: Journal Article
• Authors: Park, Jong‐Sun; Shue, Jih‐Hong; Nariyuki, Yasuhiro; Kartalev, Monio
• Is Part Of: Journal of geophysical research. Volume 124:Issue 3(2019)
• Page Start: 1866
• Page End: 1882
• Publication Date: 2019-03-28
• Subjects: magnetosheath ions -- polytropic index -- IMF orientation -- Bow shock geometry; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2018JA026108
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Using Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations over a 10‐year period from 2008 to 2017, we statistically investigate the thermodynamic properties for magnetosheath ions and their dependence on upstream interplanetary magnetic field (IMF) conditions. The thermodynamic properties for magnetosheath ions are estimated by using the polytropic index averaged over the subinterval that belongs to the same streamline ( α ¯ ). The THEMIS observations show that the probability distribution of α ¯ for magnetosheath ions has a major peak at α ¯ ~1 (quasi‐isothermal conditions) with a longer left tail down to α ¯ ~0 (quasi‐isobaric conditions). The spatial distributions of α ¯ for two different types according to IMF spiral angle (i.e., Parker spiral and ortho‐Parker spiral IMF orientations) reveal that the ions in the downstream of a quasi‐perpendicular shock (quasi‐perpendicular magnetosheath) exhibit quasi‐isothermal processes, while those in the downstream of a quasi‐parallel shock (quasi‐parallel magnetosheath) show α ¯ lower than unity (down to α ¯ ~0.8) implying the anticorrelation between the ion temperature and the ion number density variations. Moreover, α ¯ in the quasi‐parallel magnetosheath tends to decrease with increasing magnetic local time distance from the magnetic local noon. These results indicate that the thermodynamic properties for magnetosheath ions depend on the bow shock geometry (quasi‐perpendicular bow shocks versus quasi‐parallel bow shocks) and are presumably controlled by a variety of instabilities, waves, and turbulence in the magnetosheath. Key Points: The probability distribution of the polytropic index for magnetosheath ions has a major peak at 1 with a longer left tail down to 0 Ions in the quasi‐perpendicular magnetosheath exhibit quasi‐isothermal processes In the quasi‐parallel magnetosheath, the variations in the ion temperature are anticorrelated with those in the ion number density