Correlation of changes in the outer‐zone relativistic‐electron population with upstream solar wind and magnetic field measurements
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Abstract:
A study has been made of the correlation of the population of relativistic electrons in the outer‐zone magnetosphere with the properties of the solar wind (speed, density, magnetic field) during a solar minimum period. The study is based upon observations made in the Spring of 1995 with sensors aboard 1994‐026 and WIND. It is found that a large relativistic electron enhancement depends upon a substantial solar‐wind speed increase associated with precursor solar‐wind density enhancement, and, in particular, upon a southward turning of the interplanetary magnetic field.Keywords:
Heliospheric current sheet
It has been experimentaly established that there exists a normal component of magnetic field on the magnetopause and that open field lines connect polar cap with interplanetary medium. To explain this information, it is necessary to develop a quantitative theory of an open magnetosphere and to study the structure of the magnetopause. The magnetosheath and the magnetosphere are considered as a unitary system. The dissipative MHD approach is used outside the magnetopause, and the magnetostatic approach is used inside. The frozen‐in condition is valid anywhere except at the magnetopause which is considered to be a thin dissipative boundary layer separating the magnetosheath and the magnetosphere. The magnetopause thickness is proportional to R m −1/2 (where R m is the magnetic Reynolds number) and is about 100 times less than stand‐off distance. The magnetic field near the magnetopause is formed due to mutual diffusion of the magnetospheric magnetic field in the magnetosheath and IMF into the magnetosphere. The magnetospheric magnetic field component normal to the magnetopause is proportional to R m −1/2 and is about 1 nT at the dayside magnetopause. The related potential difference accross the open field lines is about 15 kV, which can be responsible for the background electric field measured in the polar caps. The portion of IMF which penetrates into the magnetosphere is proportional to R m −1/4 and is about a factor of 10 less than the IMF. The potential difference accross the polar cap is about 100 kV for the southward IMF of −10 nT.
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We examine the spacecraft potential (SP) variations near the magnetopause. In the magnetosphere the Geotail satellite often observed transient SP increase accompanied by magnetic field enhancements. This signature (SP increase and magnetic field increase) was also observed inside the magnetopause during the outbound (from the magnetosphere to the magnetosheath) and/or inbound (from the magnetosheath to the magnetosphere) magnetopause crossings. For the interval of the SP increase, the plasma density and temperature were intermediate between those of the magnetosheath and the magnetosphere, and strong enhancements of the field‐aligned bidirectional electron fluxes were observed mainly in the medium energy (∼300–450 eV) range. These observations are consistent with previous studies in the inner part of the low‐latitude boundary layer (LLBL). Thus we suggest that the transient SP increase in the magnetosphere may be a good indicator of the entry into the inner LLBL.
Magnetosheath
Plasma sheet
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Observational evidence is presented to show that the magnetosphere-magnetopause boundary was diffuse during the Pioneer 8 magnetopause traversal on December 14 and 15, 1967. This boundary was characterized by proton fluxes of significantly lower intensity than those observed in the magnetosheath. In addition, the angles of flow associated with the fluxes at the boundary were more diverse than those observed in the magnetosheath. Proton energy spectra are presented to indicate the change in the spectral shape at the boundary. The observational evidence is consistent with calculations by Axford and Dryer of a viscous magnetopause boundary layer, which is a function of an anomalous nonclassical kinematic viscosity. The observational evidence presented for the diffuse magnetosphere boundary may also be consistent with Dungey's model for reconnection of magnetic field lines and an open magnetosphere.
Magnetosheath
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The solar wind ‐ magnetosphere plasma system provides a unique opportunity to study the interaction of plasmas of different origin. One of the major challenges for our understanding of both basic plasma dynamics and the dynamics of the magnetosphere is the coupling of the solar wind plasma and the magnetosphere ‐ ionosphere system. Being the interface between the solar wind and the magnetosphere, the magnetopause controls the interaction between these plasmas. Although the plasma in the vicinity of the magnetopause is highly collisionless, a multitude of observations implies the transport of plasma, momentum and energy from the solar wind into the magnetosphere. The dynamics of the magnetosphere cannot be understood without processes which facilitate this transport.
Magnetosphere of Saturn
Magnetosphere of Jupiter
Polar wind
Magnetosheath
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