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Interplanetary magnetic field measurements by Pioneer 8 during 25 February 1969 solar activity, discussing geomagnetic storms, cosmic rays, shock fronts and ionospheric disturbances
Ten weeks of simultaneous fine time resolution data on the interplanetary magnetic field (IMF), the solar wind parameters observed by the Explorer 33 and Vela 3 satellites, the magnetic field, and the particle fluxes in the magnetotail from the Imp 3 satellite are examined together with auroral zone magnetograms monitoring substorm activity to study the magnetotail variations associated with the latitudinal changes of the IMF. It is found that the magnetotail magnetic field magnitude often increases when the north-south component of the IMF is southward; this increment is generally observed throughout the entire high-latitude tail (outside the plasma sheet). The increment is about 10% of the background field, and it increases to 20% or higher when the north-south component of the IMF increases from the usual 2 or 3 gamma to 7 or 8 gamma.
The paper examines the control of the magnetopause by the interplanetary magnetic field, noting that the solar wind pressure determines the 'zeroth-order' location of the earth's magnetopause. However, the normal stresses of the solar wind dynamic pressure are also accompanied by tangential stresses which erode the magnetopause from its equilibrium position and transport magnetic flux into the magnetotail. Finally, initial results indicate that when the magnetosheath magnetic field is southward the connection takes place in a series of flux transfer events capable of transporting 10 to the 16th Mx or more per hour.
Data from Atmosphere Explorer D for periods of strong northward interplanetary magnetic field show the following characteristic behavior in the dayside magnetospheric cusp region: energy-time spectrograms of suprathermal positive ion fluxes exhibit a characteristic 'V' pattern as the spacecraft moves toward higher latitudes; that is, with the peak in the energy spectrum falling in energy and then rising again. Convection velocities follow this pattern closely with strong east-west flows (with antisunward components) occurring in the equatorward half of the 'V' and significant sunward flows occurring in the poleward half of the 'V'. These patterns can be understood qualitatively in terms of a model of ionospheric electric potential produced by the known dependence of Birkeland current densities on magnetic activity.
Data from Atmosphere Explorer D for periods of strong northward interplanetary magnetic field are discussed. In the dayside magnetospheric cusp region energy time spectrograms of suprathermal positive ion fluxes exhibit a characteristic 'V' pattern as the spacecraft moves toward higher latitudes; that is, with the peak in the energy spectrum falling in energy and then rising again. Convection velocities follow this pattern closely with strong eastwest flows (with antisunward components) occurring in the equatorward half of the 'V' and significant sunward flows occurring in the poleward half of the 'V'. These patterns can be understood qualitatively in terms of a model of ionospheric electric potential produced by the known dependence of Birkeland current densities on magnetic activity.
Hydromagnetic wave interpretation of variations in interplanetary magnetic field observed by Mariner II
The Atmosphere Explorer C data base of Northern Hemisphere ionospheric convection signatures at high latitudes is examined during times when the interplanetary magnetic field orientation is relatively stable. It is found that when the interplanetary magnetic field (IMF) has its expected garden hose orientation, the center of a region where the ion flow rotates from sunward to antisunward is displaced from local noon toward dawn irrespective of the sign of By. Poleward of this rotation region, called the cleft, the ion convection is directed toward dawn or dusk depending on whether By is positive or negative, respectively. The observed flow geometry can be explained in terms of a magnetosphere solar wind interaction in which merging is favored in either the prenoon Northern Hemisphere or the prenoon Southern Hemisphere when the IMF has a normal sector structure that is toward or away, respectively.
Magnetic reconnection between the interplanetary magnetic field (IMF) and the geomagnetic field is thought to play a major role in the transfer of solar wind momentum and energy to the magnetosphere. As the angle between the IMF and the geomagnetic field is changed at the bow of the magnetosphere, the topological record of the location of the reconnection region should be recorded in the magnetosheath and on the magnetopause along the flanks of the tail, because the super fast flow freezes strong magnetic gradients formed in the bow reconnection regions into the plasma downstream. In this report, we present results from a three-dimensional, magnetohydrodynamic (MHD), global numerical simulation code for the location of the separatrix between unconnected IMF magnetosheath field lines and reconnected field lines which penetrate the magnetopause and connect to the polar ionosphere. The angle between the IMF direction and the line where the separatrix crosses the magnetopause is shown to be a sensitive function of the IMF clock angle. We also explain how this behavior can be used to derive an approximate relation for the dependence of the cross-polar voltage on the IMF clock angle. We conclude with a note of caution concerning the importance of physical boundary conditions in magnetoplasma simulations.
Energy flux values calculated for solar plasma in sectorial structure of interplanetary magnetic field
Filamentary interplanetary magnetic field structure effect on solar flare ground observational data
Cosmic ray anisotropy direction during solar proton events compared with concurrent interplanetary magnetic field vector direction, using Pioneer 6 data
Solar and galactic particle fluxes and interplanetary magnetic field after 1967 flare
The Pioneer 10 data concerning the heliocentric radial variation of the interplanetary magnetic field are examined. Incorporating the systematic increase in solar wind velocity observed during the mission leads to much improved agreement between the usual Parker Archimedean spiral and the data. The effects of correlations between short-period fluctuations of speed and azimuthal field are discussed. It is concluded that during the period under study they did not substantially affect the average magnetic field.
In a study of the dynamics of dayside aurora, Horwitz and Akasofu (1977) adopted the basic methodology of examining substorms which occurred during intervals when the interplanetary magnetic field was steady. By using this approach, it was possible to remove the obvious ambiguity in the interpretation of dayside auroral dynamics which arises if interplanetary medium variations are not excluded. It is believed that for an understanding of the natural, internal instability behavior of the magnetosphere it will be necessary to employ the same methodology in many 'substorm' studies. The present investigation has the objective to present some examples of substorms occurring during intervals of steady interplanetary magnetic field. Subsequently, the approximate time scales of expansion and recovery for such substorms are determined. The obtained results are compared with a substorm model proposed by Hill and Reiff (1980).
It has long been known that the periods of Pc 3, 4 pulsations on the ground correlate with the magnitude of the interplanetary magnetic field. This fact has been used to argue for an exogenic source for these pulsations. Particularly attractive candidates for the source of pulsations in this frequency range are the upstream waves of similar frequencies which are associated with populations of ions reflected from the bow shock. However, the dependence of the period of these waves on the strength of the interplanetary magnetic field has never been checked. This paper performs such a check and confirms that the upstream waves have the proper functional relationship.
Chromospheric flare identification by solar, geomagnetic, & ionospheric data and geometry of interplanetary magnetic field
Explorer XXVIII and XXXIII and Pioneer VI MAGNETOMETRIC determination of general macrostructure of interplanetary magnetic field in cislunar space
We have investigated the entry of energetic ions of solar origin into the magnetosphere as a function of the interplanetary magnetic field orientation. We have modeled this entry by following high energy particles (protons and 3 He ions) ranging from 0.1 to 50 MeV in electric and magnetic fields from a global magnetohydrodynamic (MHD) model of the magnetosphere and its interaction with the solar wind. For the most part these particles entered the magnetosphere on or near open field lines except for some above 10 MeV that could enter directly by crossing field lines due to their large gyroradii. The MHD simulation was driven by a series of idealized solar wind and interplanetary magnetic field (IMF) conditions. It was found that the flux of particles in the magnetosphere and transport into the inner magnetosphere varied widely according to the IMF orientation for a constant upstream particle source, with the most efficient entry occurring under southward IMF conditions. The flux inside the magnetosphere could approach that in the solar wind implying that SEPs can contribute significantly to the magnetospheric energetic particle population during typical SEP events depending on the state of the magnetosphere.