Earth's magnetic field

About: Earth's magnetic field is a research topic. Over the lifetime, 20360 publications have been published within this topic receiving 446747 citations. The topic is also known as: magnetic field of Earth & geomagnetic field.

Evidence for quasi-stationary reconnection at the dayside magnetopause

Abstract: The paper investigates several highly unusual encounters with the earth's magnetopause, that occurred during an approximately 5-hour period on November 22-23, 1979, when the ISEE 1 and 2 were near orbit apogee. A large decrease in the dynamic pressure exerted by the solar wind resulted in an expansion of the magnetosphere to and beyond the apogee of the ISEE 1 and 2 orbit, and the subsolar magnetopause of about 20.4 earth radii is farther than normal in geocentric distance by a factor of about 2. Field rotations varying from about 80 to 120 deg were involved in the transition from the magnetosheath to the magnetosphere, and hodograms of the tangential component of the magnetic field vector suggest that the magnetopause was a rotational discontinuity. These observations indicate that on occasion reconnection at the dayside magnetopause can be a quasi-stationary process.

By -dependent convection patterns during northward interplanetary magnetic field

Abstract: Observations of Birkeland currents, electric fields, and auroral forms in the dayside polar regions during periods of northward interplanetary magnetic field (IMF) can be unified to fit into consistent convection patterns ordered principally by the IMF By component. During periods of weak IMF By, two polar convection cells are symmetrically located on either side of the noon-midnight meridian, producing sunward convection over the pole, as previously reported. As the IMF By becomes significantly positive (negative), the dawn (dusk) convection cell expands across the northern polar cap, whereas the other cell shrinks. In the southern polar cap it is the dusk (dawn) cell which expands. During strong By this cell expansion gives the appearance of a single convection cell in the polar region. At the “collapsed” cell a large convective flow gradient is developed where reversal of the northward Bz (NBZ) Birkeland current system, antisunward polar ionospheric current, and the most intense polar cap electric fields are statistically observed. We suggest that this convection gradient region is also associated with sun-aligned arcs and the transpolar arc of the theta aurora, which are observed in the polar regions during northward IMF. The convection patterns proposed here are consistent with the antiparallel merging model in which the IMF merges with the geomagnetic field lines in the tail lobe during northward IMF intervals. The resulting convection in the tail brings plasma from the plasma sheet to the tail. This process divides the open field lines of the lobes and produces an area of closed field lines in the polar cap associated with the transpolar arc of the theta aurora.

Magnetospheric configurations from a high-resolution data-based magnetic field model

Abstract: [1] We present first results of the magnetospheric magnetic field modeling, based on large sets of spacecraft data and a high-resolution expansion for the field of equatorial currents. In this approach, the field is expanded into a sum of orthogonal basis functions of different scales, capable to reproduce arbitrary radial and azimuthal variations of the geomagnetic field, including its noon-midnight and dawn-dusk asymmetries. Combined with the existing method to model the global field of Birkeland currents, the new approach offers a natural way to consistently represent the field of both the tail and symmetrical/partial ring currents. The proposed technique is particularly effective in the modeling of the inner magnetosphere, a stumbling block for the first-principle approaches. The new model has been fitted to various subsets of data from Geotail, Polar, Cluster, IMP-8, and GOES-8, GOES-9, GOES-10, and GOES-12 spacecraft, corresponding to different activity levels, solar wind IMF conditions, and storm phases. The obtained maps of the magnetic field reproduce most basic features of the magnetospheric structure, their dependence on the geomagnetic activity and interplanetary conditions, as well as characteristic changes associated with the main and recovery phases of magnetic storms.

Helium abundance enhancements in the solar wind

Abstract: Evidence for a link between helium enhancements at 1 AU and transient coronal mass ejections is provided by the statistical analysis of 73 large helium abundance enhancement observations made by IMPs 6, 7 and 8 over 1972-1978. These events, in which helium abundance enhancement is greater than about 10%, are sporadic, sometimes clustered in time, occur approximately in phase with the solar cycle, and nearly 50% of them are associated with interplanetary shocks and/or geomagnetic activity sudden commencements. The plasma pattern associated with them is nevertheless independent of shock occurrence, and features high magnetic field strength, low alpha-proton velocity difference, and low proton temperature, suggesting that the enhancement is embedded in a closed, magnetically dominated structure that expands adiabatically. Evidence of an association between helium enhancement at 1 AU and type II and IV radio bursts in the corona is presented.

Outer-core geostrophic flow and secular variation of Earth's geomagnetic field

Abstract: In studies of the temporal variations of the main internal geomagnetic field (the secular variation or SV), it is usual to consider separately the variations of the dipolar and non-dipolar parts which appear to have different time constants. The mechanism that is generally invoked to explain the generation of SV is the advection of the lines of force of the main field by the highly conducting fluid at the top of the core. Such a mechanism involves the main field as a whole and it is not clear a priori why its two parts should behave separately. I show here that the Coriolis force will probably dominate the force budget at the top of the core and that, in such a case, the motion of the fluid involves the two parts of the field in a different way; in particular, the existing axial dipolar component is not re-engaged in the process which builds up the SV.