Engineering topics

Wenzel, K.-P.

Publications and source records attributed to Wenzel, K.-P..

49 records · Page 3

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 NTRS1984

Plasma and energetic particle structure upstream of a quasi-parallel interplanetary shock

ISEE 1, 2 and 3 data from 1978 on interplanetary magnetic fields, shock waves and particle energetics are examined to characterize a quasi-parallel shock. The intense shock studied exhibited a 640 km/sec velocity. The data covered 1-147 keV protons and electrons and ions with energies exceeding 30 keV in regions both upstream and downstream of the shock, and also the magnitudes of ion-acoustic and MHD waves. The energetic particles and MHD waves began being detected 5 hr before the shock. Intense halo electron fluxes appeared ahead of the shock. A closed magnetic field structure was produced with a front end 700 earth radii from the shock. The energetic protons were cut off from the interior of the magnetic bubble, which contained a markedly increased density of 2-6 keV protons as well as the shock itself.

Kennel, C. F.↗

NASA NTRS1984

Energetic ion regimes in the deep geomagnetic tail - ISEE-3

Bame et al. (1983) have given plasma measurements for two 12-hour intervals and have identified the plasma regions observed during the January 1-March 30, 1983 traversal by the ISEE-3 spacecraft of a previously unexplored part of the distant geomagnetic tail. Attention is presently given to the 35 keV-1.6 MeV energetic ion and magnetic field measurements made by ISEE-3, relating them to the plasma measurements. The plasma sheet is found to be a region of energetic ion enhanced fluxes, with unidirectionally tailored flow. A characterization accounting for these characteristics involves occurrence of reconnection at a neutral line that lies earthward of the spacecraft.

Cowley, S. W. H.↗

NASA NTRS1983

Correlated particle and magnetic field observations of a large-scale magnetic loop structure behind an interplanetary shock

From a survey of observations on ISEE-3, an example of correlated particle and magnetic field observations of a large-scale magnetic loop structure is presented. Bidirectional proton fluxes were observed for a period of 40 hours in the energy range 35-1600 keV approximately 12 hours after the passage of the interplanetary shock of December 11, 1980, and directly after the passage of a discontinuity. For each of the eight logarithmically spaced energy channels, a three-dimensional anisotropy analysis reveals streaming along both directions of the magnetic field. The magnetic field rotated slowly but steadily through approximately 180 deg during this same 40-hour period; this is consistent with the existence of a large-scale loop with extent greater than 0.5 AU. The observations suggest that the particles are being injected into the loop sunward of the spacecraft; they appear as bidirectional fluxes in the outermost regions of the loop arising from a combination of focusing and near scatter-free transport.

Sanderson, T. R.↗

NASA NTRS1983

A statistical study of interplanetary shock associated proton intensity increases

Large intensity increases of low-energy protons are frequently observed in connection with interplanetary forward shocks. Essentially two different particle acceleration mechanisms to explain these 'ESP events' are presently under discussion. To find out which is the dominant process for particle acceleration a large number of these events observed on ISEE-3 was analyzed. The events with the highest fluxes of 35-56 keV protons are associated with shocks which are quasi-parallel and originate close to the central meridian of the sun, and it is concluded that they are produced by a first order Fermi acceleration process.

Reinhard, R.↗

NASA NTRS1983

ISEE/IMP observations of simultaneous upstream ion events

Propagation of upstream energetic (50-200 keV) ions is analyzed in sixteen events observed simultaneously by solid state detectors on ISEE 3 at about 200 earth radii and on IMP 8 at about 35 earth radii from the earth. Conclusions are based on comparisons of the pitch angle distributions observed at the two spacecraft and transformed into the solar wind frame. They are beamlike at ISEE 3 and are confined to the outward hemisphere. When IMP 8 is furthest from the bow shock, they are also usually beamlike, or hemispheric. However, when IMP 8 is closer to the bow shock, pancakelike distributions are observed. This systematic variation in the IMP 8 pitch angle distributions delimits a scattering region l less than about 15 earth radii upstream of the earth's bow shock (l measured along the interplanetary magnetic field) that dominates ion propagation, influences the global distribution of fluxes in the foreshock, and may play a role in acceleration of the ions. When IMP 8 is beyond l of about 15 earth radii the propagation appears to be essentially scatter-free between IMP 8 and ISEE 3; this is deduced from the absence of earthward fluxes at IMP 8 as well as the tendency for the spin-averaged fluxes to be comparable at the two spacecraft.

Mitchell, D. G.↗

NASA NTRS1983

Observations of upstream ions and low-frequency waves on ISEE 3

Three examples are presented of observations of upstream ions and low-frequency waves made at ISEE 3 at distances of up to 200 earth radii upstream from the earth's bow shock. The observations demonstrate that even at 200 earth radii, weak scattering plays an important role in the transport of upstream ions. At ISEE 3, during long-lasting events, a correlation is observed between the growth of the waves and the intensity of the upstream ions. An increase in the number of pitch-angle-scattered ions, frequently with a moderate amount of ions having pitch angles greater than 90 deg, is observed, and this is correlated with the growth of the waves. It is concluded that during long-lasting events an equilibrium is reached where the region between the spacecraft and the bow shock contains a significant amount of low-frequency wave activity, together with significant pitch angle scattering.

Sanderson, T. R.↗

NASA NTRS1983

The ISPM Mission - Science objectives and mission overview

The International Solar Polar Mission (ISPM) will, for the first time, allow exploration of the heliosphere within a few astronomical units of the sun over the full range of heliographic latitudes. The prime mission objective is to study, as a function of solar latitude, the properties of the interplanetary medium and solar corona. The scientific instrumentation is designed to explore, in the third heliospheric dimension, the properties of the solar wind, the sun/wind interface, the heliospheric magnetic field, solar radio bursts and plasma waves, solar X-rays, solar and galactic cosmic rays, and interplanetary/interstellar neutral gas and dust. ISPM will also detect cosmic gamma-ray bursts and search for gravitational waves. ISPM is a cooperative mission carried out jointly by ESA and NASA, to be launched in May 1986 and utilising a Jupiter gravity-assist to achieve a high-solar-latitude trajectory.

Wenzel, K.-P.↗

NASA NTRS1983

The interplanetary shock event of November 11/12 1978 - A comprehensive test of acceleration theory

A comprehensive study of the November 11, 12, 1978 shock event based on energetic particle, solar wind, magnetic field and wave data from the ISEE-3, -1 and -2 spacecraft has been undertaken both from the energetic and the collisionless shock point of view. The energy density of 10-50 keV protons accelerated by the shock is found to be equivalent to the upstream magnetic field energy density. The observations are in quantitative agreement with Lee's (1983) self consistent theory for the excitation of hydromagnetic waves and the acceleration of ions upstream of interplanetary shocks.

Wenzel, K.-P.↗

NASA NTRS1983

ISEE-3 observations of 35-1600 keV protons and low frequency waves upstream of an interplanetary shock

An example of observations of 35-1600-keV protons and low-frequency waves (period about 20 s) associated with the passage of an interplanetary shock at ISEE-3 is presented. For several hours prior to the arrival at the spacecraft of the quasi-parallel shock of April 5, 1979, enhanced fluxes of 35-1600-keV protons and large-amplitude low-frequency waves were observed. During most of this period the spectrum was dominated by particles with energies of about 200 keV. The amplitude of the waves is well correlated with the proton intensity at these energies, suggesting a close relation between the waves and the particles.

Sanderson, T. R.↗

NASA NTRS1982

ISEE-3/IMP-8 observations of simultaneous upstream proton events

Upstream 50-200 keV proton events were observed simultaneously by the low energy proton detectors on ISEE-3 and IMP-8, and the gradient from the spin averaged fluxes at the two spacecraft was calculated. The dependence of that gradient upon the angular distributions at IMP-8 was investigated as well as the distance from IMP-8 to the bow shock. The pitch angle distributions are narrow at ISEE-3 and wide and often pancake-shaped at IMP-8 with a peak near 90 degrees. This implies the existence of a weak scattering region about 5-15 earth radii upstream of the earth's bow shock.

Sanderson, T. R.↗

NASA NTRS1978

Rigidity-independent coronal propagation and escape of solar protons and alpha particles

In a study of rigidity-independent coronal propagation processes, data on the azimuthal variation of the solar proton/alpha-particle ratio were obtained. Sources for the data included a statistical analysis of events observed by Heos-2, a comparative study of events recorded by both Heos-2 and Pioneer-10 and -11, and a multiday survey of individual events observed by Heos-2 and Pioneer-10. The statistical investigation of Heos-2 events reveals an increase of the lower value of the proton/alpha-particle ratio away from the well-connected region. The data from one or two spacecraft connected at different heliolongitudes indicates no azimuthal dependence of the proton/alpha-particle ratio. All the data appear to suggest rigidity-independent propagation or escape processes.

Perron, C.↗

NASA NTRS1975

Splash albedo protons between 4 and 315 MeV at high and low geomagnetic latitudes

Results are reported for measurements of the differential energy spectrum of splash-albedo protons at high geomagnetic latitude during three periods of the last solar cycle as well as at low latitude during one of those periods. The measurements were made with a balloon-borne solid-state detector telescope. Splash-albedo protons with energies between 4 and 315 MeV were observed in fluxes of approximately 81, 70, and 48 protons/sq m per sec per sr at high latitude and in fluxes of approximately 37 protons/sq m per sec per sr at low latitude. It is shown that the difference between the first and third high-latitude measurements was due to solar modulation of the cosmic-ray parent nuclei. The albedo spectrum is found to have a similar shape for both latitudes, and it is suggested that the difference in intensity can be explained by different local geomagnetic cutoffs.

Wenzel, K.-P.↗