Dipole model of the Earth's magnetic field

About: Dipole model of the Earth's magnetic field is a research topic. Over the lifetime, 2756 publications have been published within this topic receiving 83021 citations.

Relevance of cme to the structure of large-scale solar magnetic fields

Abstract: The relevance of the occurrence rate and location of CME events to two main systems (giant and supergiant) of the large-scale solar magnetic field structure has been investigated. The clustering of CME events and solar flares toward the neutral line of the global field system (neutral line of the source surface field) corroborates the finding by Hundhausen that CME locations track the heliomagnetic equator. A good correlation has been revealed between the CME occurrence rate and variations of the index of the effective solar multipole, that characterizes the typical scale of the global solar magnetic field. The CME rate exhibits sharp jumps/decreases when the index of the effective solar multipole passes through n=4. The observations of X-ray 'blow-out' effects have been analyzed as probable manifestations of CMEs on the disk and have been compared with the large-scale magnetic field structure. As shown by the analysis, the X-ray arcades straddle the neutral line and occur, or at least tend to occur, where the neutral line exhibits a sharp bend. A conclusion is made that CME events are caused by interaction of two large-scale field systems, one of them (the global field system) determining the location of CMEs and another (the system of closed magnetic fields) their occurrence rate.

Interaction of a magnetic dipole with a slowly moving electrically conducting plate

Abstract: We report an analytical investigation of the force and torque acting upon a magnetic dipole placed in the vicinity of a moving electrically conducting nonmagnetic plate. This problem is relevant to contactless electromagnetic flow measurement in metallurgy and extends previous theoretical works (Thess et al., Phys Rev Lett 96:164501, 2006; New J Phys 9:299, 2007) to the case where the orientation of the magnetic dipole relative to the plate is arbitrary. It is demonstrated that, for the case of low magnetic Reynolds number, the three-dimensional distributions of the induced electric potential, of the eddy currents, and of the induced magnetic field can be rigorously derived. It is also shown that all components of the force and torque can be computed without any further approximation. The results of the present work serve as a benchmark problem that can be used to verify numerical simulations of more complex magnetic field distributions.

Global-scale external magnetic fields at Mars measured at satellite altitude

Abstract: The martian magnetic field is unique among those of the terrestrial planets It is the net result of the interaction of the solar wind and the interplanetary magnetic field (IMF) with crustal remnant magnetization and a planetary ionosphere Internal fields of crustal origin have been the subject of extensive studies; the focus of our work is identification and characterization of contributions from external magnetic fields using the Mars Global Surveyor (MGS) vector magnetic field data We investigate the magnitude, average spatial structure and temporal variability of the external magnetic field at MGS mapping altitude of 400 km by first subtracting the expected contributions from crustal fields using existing global crustal field models We identify periodicities and spatial structure in the field related to the day-night cycle and Carrington rotations, as well as variations corresponding to an annual cycle and short aperiodic signals We suggest that ionospheric currents driven by upper atmosphere winds contribute to the observed zonal structure in the daily variation in the external magnetic field Finally, we discuss the potential for magnetic sounding studies using time-varying external fields and surface magnetometry measurements from the InSight mission to be launched in 2018

MORPHOLOGY OF OUTER RADIATION ZONE ELECTRON (E > 35 keV) ACCELERATION MECHANISMS.

Abstract: A study of outer radiation zone electron intensities at times of magnetic storms is reported. The purpose of the study is to determine how well the intensity at one local time tracks the intensity at the same invariant latitude but at a different local time. Any difference in the intensity time profiles might be expected to yield information about the mechanisms responsible for acceleration of outer-zone electrons, particularly the locations of these mechanisms. The measurements refer to selected periods of several days each and have been obtained at altitudes below 3500 km, invariant latitudes in the range 50° to 72°, and at several pairs of local times. At times of magnetic storms the tracking at the two local times is often quite poor at latitudes as low as 55°. For short periods around local midnight and on the morning side of the earth the intensities observed are appreciably higher than those on the afternoon side. It is concluded from these observations that most of the storm-time acceleration of electrons to energies about 35 kev takes place on the night and morning sides of the earth. The measurements are used to place an upper limit on stably trapped fluxes in the outer radiation zone that agrees reasonably well with the whistler mode limiting flux calculated by Kennel and Petschek [1966].

Ionospheric effects of magnetospheric and thermospheric disturbances on March 17–19, 2015

Abstract: Using vertical and oblique radio-sounding data, we analyze the ionospheric and thermospheric disturbances during the magnetic storm that occurred in northeastern Russia on March 17–19, 2015. We consider the heliospheric sources that induced the magnetic storm. During the main and early recovery phases, the midlatitude stations are characterized by extremely low values of electron density at the F2 layer maximum. Using oblique sounding data, we recorded signals that propagated outside the great circle arc. In evening and night hours, no radio signals were found to pass along the Norilsk–Irkutsk and Magadan–Irkutsk paths. The observed ionospheric effects are shown to be caused by a sharp shift of the boundaries of the main ionospheric trough to the invariant latitude 46° N during the main phase of the magnetic storm. The negative ionospheric disturbance during the recovery phase of the storm, which was associated with significant variations in the composition of the neutral atmosphere, led to a change in the mode composition of received radio signals and a decline in observed maximal frequencies in daytime hours of March 18, 2015 by more than 2 times.