Evolution of a typical ion‐scale magnetic flux rope caused by thermal pressure enhancement. Issue 2 (28th February 2017)

• Record Type: Journal Article
• Authors: Teh, W.‐L.; Nakamura, T. K. M.; Nakamura, R.; Baumjohann, W.; Russell, C. T.; Pollock, C.; Lindqvist, P.‐A.; Ergun, R. E.; Burch, J. L.; Torbert, R. B.; Giles, B. L.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 2(2017)
• Page Start: 2040
• Page End: 2050
• Publication Date: 2017-02-28
• Subjects: magnetic flux ropes -- magnetopause; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2016JA023777
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: With high time‐resolution field and plasma measurements by the Magnetospheric Multiscale spacecraft, interior fine structures of two ion‐scale magnetic flux ropes (~5 and ~11 ion inertial length radius) separated by ~14 s are resolved. These two ion‐scale flux ropes (FR1 and FR2) show non‐frozen‐in ion behavior and consist of a strong axial magnetic field at the reversal of the negative‐then‐positive bipolar field component. The negative bipolar field component of the FR2 is found to be depressed, where magnetic pressure and total pressure decrease, but ion and electron thermal pressures increase, a feature akin to a crater‐like flux rope. The pressure enhancement is due to the magnetosheath plasma feeding into the flux rope along the field lines. Magnetic field draping and energetic electrons are also observed in the trailing part of the FR2. The ratio of perpendicular and parallel currents indicates that the FR1 appears force‐free but the FR2 seems not. Moreover, the FR2 is time‐dependent as a result of a low correlation coefficient (CC = 0.75) for the derivation of the deHoffmann‐Teller frame using the direct measured electric fields, while the FR1 is in quasi‐steady conditions (CC = 0.94). It is concluded that the crater formation within the FR2 can be interpreted by the analytical flux rope simulation as the evolution of typical flux rope to crater‐like one due to the thermal pressure enhancement, which could be induced by the depression of transverse magnetic fields of the flux rope. Key Points: Interior fine structures of two ion‐scale flux ropes are resolved for which some of their flux rope properties are contrasted Crater is formed within one flux rope where magnetic pressure decreases while thermal pressure increases Crater formation can be interpreted by flux rope simulation as evolution of typical flux rope to crater‐like one due to pressure increase