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At least 217 records · Page 12

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NASA NTRS1985

Observations of 35- 10 1600-keV protons and low-frequency waves upstream of interplanetary shocks

The present investigation is concerned with a comparison of measurements of energetic protons in the range from 35 to 1600 keV and low-frequency waves (periods of approximately 6 s) on ISEE 3 associated with the passage of the large oblique shock of April 5, 1979, which exhibits an extended foreshock. An attempt is made to identify the energy of the particles which are responsible for the waves. Intensity profiles of both waves and particles as a function of upstream distance are compared, taking into account the relation between the energy of the particles and the period of the waves. The considered approach makes it possible to identify protons with energies of a few hundred keV as being responsible for the waves in the extended foreshock. It is believed that the high energy density of the high-energy solar flare protons preceding the shock could be responsible for 'seed' waves which provide the scattering centers necessary for the acceleration of the lower-energy protons via a first-order Fermi mechanism.

Sanderson, T. R.↗

NASA NTRS1985

Interplanetary shock phenomena beyond 1 AU

Attention is given to spatial dependences exhibited by spacecraft measurements obtained between 1 and 30 AU, together with temporal variations occurring between solar activity cycle maxima and minima. At 1-3 AU radial distances, shocks develop in association with the corotating solar wind streams characterizing solar minimum and accelerate solar wind evolution with distance while heating the solar wind and generating waves and turbulence. At solar maximum, shocks are observed more frequently at 1 AU but still in association with transient solar events; acceleration leading to energetic storm particles is observed both within and beyond 1 AU. The superimposed effect of large numbers of intense shocks may be responsible for the solar cycle modulation of galactic cosmic rays.

Smith, Edward J.↗

NASA NTRS1991

Solar particle abundances at energies of greater than 1 MeV per nucleon and the role of interplanetary shocks

The abundances of elements in large solar energetic-particle events in the energy range of 2-12 MeV per nucleon are examined. It is confirmed that the abundances relative to mean values vary approximately monotonically as a function of mass, except for He-4; some events show a gradual depletion of heavy ions, whereas a small number displays a gradual increase. A further organization of abundance data is shown, which depends on the longitude of the source region. Enhancements in Fe/C and other heavy elements relative to C occur when source regions are near west 60 deg; the enhancements are attributed to the sampling of a flare-heated material. Depletions of these elements are found to be greatest for source regions near central meridian; they are matched by a steepening of the spectrum and can be understood in terms of diffusive shock acceleration.

Cane, H. V.↗

NASA NTRS1992

Mass-loading at interplanetary shocks

Mass-loading fronts represent a new class of shocks which is found frequently in the solar system, both at the head of comets and upstream of weakly and nonmagnetized planets, and which has not yet been investigated in great detail. Here, a general theoretical description of mass-loading shocks (MLSs) in the heliosphere is presented and the difference between MLSs and classical nonreacting MHD shock are elucidated. It is found that the momentum contribution of added mass within the shock represents a physically important effect, particularly in the shock strength regime observed at Comets Halley and GZ. The mass-loading MHD Rankine-Hugoniot conditions are not tangentially invariant, so mass-loading fronts are subjected to shearing stresses, greatly curtailing the upstream parameter regime for which stable transitions are possible. The existence of fast and slow mode compound mass-loading fronts is predicted. Other forms of mass-loading fronts exist for which no classical MHD counterparts exist.

Zank, G. P.↗

NASA NTRS1993

Comment on 'Geomagnetic activity associated with earth passage of interplanetary shock disturbances and coronal mass ejections' by J. T. Gosling, D. J. McComas, J. L. Philips, and S. J. Bame

It is contended that statistical data do not support the claim of Gosling et al. (1991) to the effect that the initial speed of a solar wind driver gas close to the sun appears to be the most crucial factor in determining if an earthward direct event will be effective in exciting a large geomagnetic disturbance. It is argued that the time intervals are much too large to observe the storm-time B sub Z dependence. Gosling et al. reply that this comment is based on a serious misunderstanding of their conclusions.

Tsurutani, Bruce T.↗

NASA NTRS2000

The Immediate Auroral Response to Interplanetary Shock Event

The auroral response to the dynamic solar wind is generally thought of as having a time lag of several minutes to hours. However, with the simultaneous and continuous availability of global images and solar wind data for several hours has enabled the direct and immediate response of the aurora to be observed. Localized as well as large scale phenomena have been observed nearly simultaneously with sudden variances in the solar wind density and velocity. A review of the historical and recent progress in this area of research will be presented.

Spann, James F.↗

NASA NTRS2001