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At least 811 records · Page 45
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NASA NTRS1984

The international Halley Watch

The schedule of ground-based and extraterrestrial observations planned for comet Halley during the International Halley Watch (IHW) program is briefly described. A schematic diagram is presented in order to illustrate the lines of communication between the administrators, discipline specialists, and amateur observers participating in IHW. The specific observational activities schedule for the IHW in early late 1985 and early 1986 include: infrared spectroscopic and radiometric observations; photometry and polarimetry, and near nucleus studies. The satellite observation platforms of the IHW will include, the Giotto, VEGA, ISEE-3, and Plant A satellites.

West, R. M.↗
NASA NTRS1985

Characteristics of the white-light source in the 1981 April 24 solar flare

Observations of the white-light solar flare event of April 24, 1981 are presented. The observations were carried out in the optical, hard X-ray, and radio wavelengths from land-based observatories and from the International Sun-Earth Explorer (ISEE-3) satellite. Time-intensity profiles were derived for three lines of continuum emissions. The derived profiles are interpreted in terms of the energetics of the flare, and the role of energetic electrons in the production of optical continuum emission is examined in detail.

Kane, S. R.↗
NASA NTRS1985

The polar ionosphere as a source of the storm time ring current

The transport of ions from the polar ionosphere to the inner magnetosphere during storm time conditions has been computed using a Monte Carlo diffusion code. The effect of the electrostatic turbulence assumed to be present during the substorm expansion phase was simulated by a process that accelerated the ions stochastically perpendicular to the magnetic field with a diffusion coefficient proportional to the rate of energization of the ions by the induced electric field. This diffusion process was continued as the ions were convected from the plasma sheet boundary layer to the double-spiral injection boundary. Inward of the injection boundary the ions were convected adiabatically. By using as input an O(+) flux of 2.8 x 10 to the 8th per sq cm per s (w greater than 10 eV) and an H(+) flux of 5.5 x 10 to the 8th per sq cm per s (w greater than .63 eV) the computed distribution functions of the ions in the ring current were found to be in good agreement, over a wide range in L (4-8), with measurements made with the ISEE 1 satellite during a storm. This O(+) flux and a large part of the H(+) flux appear to be consistent with the DE-1 and DE-2 satellite measurements of the polar ionospheric outflow during disturbed times.

Cladis, J. B.↗
NASA NTRS1985

A comparison of solar helium-3-rich events with type II bursts and coronal mass ejections

The acceleration process for energetic particles in He-3-rich events and for particles in normal-abundance events are compared. A list of 66 He-3-rich events observed with the Goddard Space Flight Center particle detector on ISEE 3 is presented, and it is shown that these events are not statistically associated with either of the two common signatures of normal-abundance events, metric type II and coronal mass ejections. This result indicates that enhanced abundance events may be produced only in the impulsive phases of flares, while normal abundance events are produced in subsequent flare shock waves.

Kahler, S.↗
NASA NTRS1985

Configuration of the high-latitude thermosphere neutral circulation for IMF B(y) negative and positive

Asymmetries in the Northern Hemisphere neutral circulation that are dependent on the sign of the east-west 'B(y)' component of the IMF are presently illustrated by measurements of the neutral wind in the polar F-region which were conducted by the DE-2 spacecraft. The data thus obtained are categorized according to the sign of the hourly averaged IMF B(y) component measured by ISEE-3 for the hour preceding the DE-2 measurements. It is noted that there is (1) an asymmetry in the polar cap neutral flow velocity, with the region of most rapid antisunward flow shifting from the dawn side to the dusk side of the polar cap as B(y) changes from positive to negative; (2) a shift occurs in the magnetic local time of the region of entry of neutral gas into the polar cap, from a location on the dawn side of the moon-midnight meridian for B(y) positive to one more biased, for B(y) negative; and (3) there is an enhancement of velocities associated with the dawn anticlockwise neutral vortex for B(y) negative relative to those observed for B(y) positive.

Mccormac, F. G.↗
NASA NTRS1985

New results on the Pioneer Venus Orbiter February 10-11, 1982 events - A solar wind disturbance not a comet

The characteristics of a series of disturbances observed on February 10-11, 1982 by the plasma analyzer and the magnetometer on the Pioneer Venus Orbiter, obtained in the solar wind upstream of Venus are studied. It is concluded that the events were associated with the propagation of a solar wind disturbance of coronal origin and not with an encounter with a comet or other local outgassing object (Russel, et al., 1983). The plasma analyzer spectra clearly show the presence of increases in He(2) and they argue strongly against Russell, et al.'s interpretatation. The peak in magnetic field magnitude on February 11 is identified as the magnetic signature of a thin, trailing 'filament' at the end of a series of solar-initiated events. Corresponding increases in He(2) and magnetic field fluctuations were observed near earth by ISEE-3 about a day later, and this strongly supports the concept of a solar origin.

Intriligator, D. S.↗
NASA NTRS1985

Energetic particle characteristics of magnetotail flux ropes

During the recent ISEE-3 Geotail Mission three events have been identified from the magnetometer data which are consistent with a spacecraft crossing of a magnetotail flux rope. Energetic electron and proton observations obtained by the Max-Planck-Institut/University of Maryland sensor system during two of the possible flux rope events are presented. During one event remote sensing of the flux rope with energetic protons reveals that the flux rope is crossed by the spacecraft from south to north. This allows determination of the bandedness of the magnetic field twist and of the flux rope velocity relative to the spacecraft. A minimal flux rope radius of 3 earth radii is derived. Energetic proton intensity is highest just inside of the flux rope and decreases towards the core. Energetic electrons are streaming tailward near the outer boundary, indicating openness of the field lines, and are isotropic through the inner part of the flux rope.

Scholer, M.↗
NASA NTRS1985

The downshift of electron plasma oscillations in the electron foreshock region

Electron plasma oscillations in the earth's electron foreshock region are observed to shift above and below the local electron plasma frequency. As plasma oscillations shift downward from the plasma frequency, their bandwidth increases and their wavelength decreases. Observations of plasma oscillations well below the plasma frequency are correlated with times when ISEE 1 is far downstream of the electron foreshock boundary. Although wavelengths of plasma oscillations below the plasma frequency satisfy k x lambda-De approximately 1 the Doppler shift due to the motion of the solar wind is not sufficient to produce the observed frequency shifts. A beam-plasma interaction with beam velocities on the order of the electron thermal velocity is suggested as an explanation for plasma oscillations above and below the plasma frequency. Frequency, bandwidth, and wavelength changes predicted from the beam-plasma interaction are in good agreement with the observed characteristics of plasma oscillations in the foreshock region.

Fuselier, S. A.↗
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

Polar rain - Solar coronal electrons in the earth's magnetosphere

Low energy electron measurements collected by ISEE 1 reveal the frequent presence of field-aligned fluxes of few hundred eV electrons in the geomagnetic tail lobes. In the northern tail lobe these electrons are most prominent when the interplanetary magnetic field is directed away from the sun. This characteristic helps identify the electrons as polar rain electrons. By mapping the tail lobe velocity distribution function into the solar wind, previous suggestions that the polar rain is indeed of solar wind origin and is due to the access of electrons to the magnetotail lobe were confirmed. It was demonstrated that the more energetic component of the polar rain is composed of electrons from the solar wind strahl - a field-aligned component of the solar wind which is difficult to measure but which is thought to be caused by the collisionless transit of hundred eV electrons from the inner solar corona to 1 AU.

Fairfield, D. H.↗
NASA NTRS1985

Observations of a possible ground signature of flux transfer events

Questions regarding the mechanism by which the large-scale cross-tail electric field and associated convection in the magnetosphere is maintained have not yet been completely answered. According to Dungey (1961), the boundary layer (BL) inside the magnetopause (MP) in which the tailward transport of mass, momentum, and magnetic flux takes place can be produced by reconnection. Observations made with the aid of the ISEE spacecraft show that reconnection can occur both in a quasisteady form and in a more unsteady form known under the name 'flux transfer event' (FTE). The present investigation proposes observation of the ground signature of an FTE. It is pointed out that the STARE radar system has the potential for making observations pertinent to identifying and studying the ionospheric signatures of FTE's. An analysis is conducted of two periods during which the convective boundary (CB) moved into the STARE field of view. The significance of the observations is discussed.

Goertz, C. K.↗
NASA NTRS1985

Cold streams of ionospheric oxygen in the plasma sheet during the CDAW 6 event of March 22, 1979

During magnetospheric substorm events, the plasma and ion composition experiments in the ISEE-1 and 2 satellites detected cold ionospheric O+ streams, moving tailwards in the near earth magnetotail. Flow is parallel to the magnetic field lines, with drift velocity in agreement with the electric field topology obtained by mapping the model ionospheric field along the magnetic field lines. Fluctuations of the flow velocity of the streams can be related to magnetotail movements. Oscillations of the flow direction and speed with periods ranging from 5 to 10 min that suggest the presence of waves are observed. The streams are observed at all distances between 15 and 6 Re from the earth. When averaged over 360 deg, the streams show up as a low energy peak, superimposed on the distribution of isotropic plasma sheet ions. This double-peak structure of the energy spectrum seems typical of the disturbed plasma sheet.

Orsini, S.↗
NASA NTRS1985

Response of earth and Venus ionospheres to corotating solar wind stream of 3 July 1979

Corotating solar wind stream interactions are examined for the earth and Venus in light of data from the plasma detectors aboard ISEE-3, the Pioneer Venus Orbiter (PVO), and Helios-A, as well as in situ ion composition measurements taken by the mass spectrometers aboard the PVO and Atmosphere Explorer-E spacecraft. During May-July 1979, a sequence of distinct, recurrent coronal regions developed at the sun; their analysis indicates a corresponding sequence of corotating streams. Although the planetary environments are distinctly different, it is noted that pronounced and analogous ionospheric responses to the stream passage were observed at both the earth and Venus. The response to the intercepted stream is consistent with independent investigations showing the importance of the variability of the solar wind momentum flux in the solar wind-ionosphere interaction at both planets.

Taylor, H. A., Jr.↗
NASA NTRS1985

AMPTE/CCE magnetic field studies of the September 4, 1984 storm

The AMPTE/CCE (active magnetospheric particle tracer explorer/charge composition explorer) magnetic-field observations acquired during the September 4, 1984 geomagnetic storm are described. The observations are used to determine magnetospheric regions and boundaries and are also used as the primary index of the development, evolution, and distribution of the ring current. The results of an analysis of the observations are presented. It is shown that a magnetic compression observed inside the magnetosphere by CCE and outside by ISEE-2 is interpreted as a sudden impulse. From an estimation of magnetopause normals at each crossing, it is concluded that the magnetic variations that occur are due to a contraction and expansion of the entire magnetosphere. Local magnetic-field depressions are observed during two inbound dusk passes, confirming that the ring current never developed in the dawn sector.

Potemra, T. A.↗
NASA NTRS1985

Defect-phase-dynamics approach to statistical domain-growth problem of clock models

The growth of statistical domains in quenched Ising-like p-state clock models with p = 3 or more is investigated theoretically, reformulating the analysis of Ohta et al. (1982) in terms of a phase variable and studying the dynamics of defects introduced into the phase field when the phase variable becomes multivalued. The resulting defect/phase domain-growth equation is applied to the interpretation of Monte Carlo simulations in two dimensions (Kaski and Gunton, 1983; Grest and Srolovitz, 1984), and problems encountered in the analysis of related Potts models are discussed. In the two-dimensional case, the problem is essentially that of a purely dissipative Coulomb gas, with a sq rt t growth law complicated by vertex-pinning effects at small t.

Kawasaki, K.↗
NASA NTRS1985

The ionospheric contribution to the plasma environment in near-earth space

SCATHA and ISEE 1 satellite ion mass spectrometer data on ion composition near GEO are reviewed. The data were gathered during and close to magnetic storm activity to assess the characteristics of ion composition variations in order to predict the effects of hot GEO plasma on spacecraft instruments. Attention is given to both substorms and storms, the former being associated, at high latitudes, with auroral activity, the latter with ring currents. The ionosphere was found to supply hot H(+), O(+) and He(+) ions to the GEO magnetosphere, while the solar wind carried H(+) and He(+) ions. The ionosphere was the dominant source in both quiet and storm conditions in the inner magnetosphere.

Sharp, R. D.↗
NASA NTRS1985

Solar He-3-rich events and nonrelativistic electron events - A new association

In 15 months of observation by the ISEE-e spacecraft, it was found that virtually all solar greater than or approximately equal to 1.3 MeV/nucleon He-3-rich events are associated with impulsive 2 to approximately 100 keV electron events, although many electron events were not accompanied by detectable He-3 increases. Both the He-3 and the electrons exhibit nearly scatter-free propagation in the interplanetary medium, and the times of onset and maximum for the He-3 and electron increases are closely related by velocity dispersion. The electron events and their related type III solar radio bursts provide, for the first time, identification of the flares which produce the He-3-rich events. He-3 appears to be accelerated at the flash phase of solar flares along with nonrelativistic electrons.

Reames, D. V.↗
NASA NTRS1985

Interplanetary magnetic field enhancements in the solar wind Statistical properties at 1 AU

The present investigation is concerned with interplanetary magnetic field (IMF) enhancements which do not resemble any of the previously reported amplifications in the IMF. The magnetic field enhacements observed increase slowly at first and then more rapidly to a peak followed by a symmetrical decay. Interplanetary magnetic field enhacement observed by ISEE-3 on various dates are considered, giving attention to observations on June 5, 1979; September 8-9, 1980; February 5, 1981; and June 14-15, 1981. Interplanetary magnetic field enhancement observed with the aid of IMP-8 are also considered. A total of 45 events is found in surveying a 9-year period of magnetic field data.

Arghavani, M. R.↗