Interplanetary Magnetic Field Bx Component Influence on Horizontal and Field‐Aligned Currents in the Ionosphere. Issue 5 (2nd May 2018)

• Record Type: Journal Article
• Authors: Laundal, K. M.; Reistad, J. P.; Finlay, C. C.; Østgaard, N.; Tenfjord, P.; Snekvik, K.; Ohma, A.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 5(2018)
• Page Start: 3360
• Page End: 3379
• Publication Date: 2018-05-02
• Subjects: ionospheric currents -- IMF Bx -- hemispheric asymmetries -- solar wind‐magnetosphere coupling; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2017JA024864
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Statistical analyses have shown that the sunward component of the interplanetary magnetic field, B x (Geocentric Solar Magnetospheric), moderately but significantly affects the auroral intensity. These observations have been interpreted as signatures of a similar interplanetary magnetic field B x control on Birkeland currents yet to be observed directly. Such a control, attributed to differences in magnetic tension on newly opened magnetic field lines, would lead to stronger region 1 (R1) Birkeland currents for B x negative (positive) conditions in the Northern (Southern) Hemispheres than when B x is positive (negative). In this paper we perform a detailed investigation of three different sets of magnetic field measurements, from the Challenging Minisatellite Payload and Swarm low Earth orbit satellites, from the Active Magnetosphere and Planetary Electrodynamics Response Experiment products derived from the Iridium satellite constellation, and from the SuperMAG ground magnetometer network, each analyzed using different techniques, to test these predictions. The results show that a change in sign of B x changes the Birkeland currents by no more than ≈10%. The current patterns show little support for an interhemispheric asymmetry of the kind proposed to explain auroral observations. Instead, we propose an alternative interpretation, which is consistent with most of the auroral observations and with the current observations in the present paper, except for those based on Active Magnetosphere and Planetary Electrodynamics Response Experiment: The solar wind‐magnetosphere coupling is more efficient when the dipole tilt angle and B x have the same sign than when they are different. We suggest that the higher coupling is because the dayside reconnection region is closer to the subsolar point when the dipole tilt angle and B x have the same sign. Plain Language Summary: The energy that powers geomagnetic activity and auroras originate in the solar wind. The most important parameters controlling the energy transfer is the solar wind velocity and the orientation of the magnetic field which is being carried by the solar wind. More energy will be transferred when this magnetic field is southward than when it is northward. Its component in the Earth‐Sun direction is most often neglected, although some studies have shown that it has a modest influence on the intensity of auroras. In this paper we search for corresponding effects in electric currents in near‐Earth space. We find that the sunward component of the magnetic field does seem to influence the currents, although not in the way suggested to explain the aurora observations. Instead, we propose that the sunward component of the interplanetary magnetic field modulates the rate at which energy is being transferred from the solar wind to the magnetosphere in a way which is different for different orientations of the Earth's magnetic field with respect to the Sun. Key Points: Three different observational tests are carried out in search of B x effects on currents Only small differences are observed between different signs of B x when B z <0 Observations indicate stronger SW‐M coupling when B x and dipole tilt have the same sign