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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Neutral sheet crossings by ISEE-3 in the distant magnetotail

The magnetic field data from ISEE-3 in the distant magnetotail at crossings of the field reversal (or neutral sheet) region are analyzed to determine the instantaneous direction of the normal component B(z) at the crossing. Crossings in the middle of the aberrated magnetotail near the apogee A2 of the first deep-tail orbit of ISEE-3 in January-February, 1983 were selected. Data for an interval of one hour is discussed at length to illustrate some of the difficulties that can occur. One particular smooth crossing at 15:56 UT, February 4, 1983, shows that complicated microstructure can occur in times shorter than one minute; averaging over long times may eliminate essential information for this purpose. By inspecting the magnetic field data at the highest resolution, however, it is shown that the direction of the plasma sheet flows and the sense of B(z) across the neutral sheet do not always agree with the reconnection models. Rather, they indicate that the low latitude boundary layer may play a significant role in the dynamics of the magnetotail.

Heikkila, W. J.↗
NASA NTRS1984

Substorm electric fields in the earth's magnetotail

A survey has been made of all the electric field data from the University of California, Berkeley, double probe experiment on ISEE-1 (apogee approximately 22 earth radii) during 1980 when the satellite was in the magnetotail. This study was restricted to the 74 events where E cross B flows could be calculated and were equal to or greater than 100 km/s. Substorm times were determined by examining the Ae index for peaks equal to or greater than 250 gamma. In association with substorms, approximately 70 percent of the flows were earthward, and approximately 20 percent had a signature called 'near satellite reconnection' (first described by Nishida et al. (1983) of tailward flow followed by earthward flow which can be interpreted in terms of a model where the x-line forms earthward of the satellite and subsequently propagates tailward of X(GSM) = -21 earth radii and within the absolute value of Y(GSM) equal to or less than 4.5 earth radii. These data suggest that the near earth x-line usually forms tailward of X(GSM) approximately -20 earth radii.

Cattell, C. A.↗
NASA NTRS1986

Earth's compressional foreshock boundary revisited Observations by the ISEE 1 magnetometer

A 'solar foreshock coordinate' (SFC) system is introduced in which the positions of foreshock components can be collated with a minimum of assumptions about the physical processes involved. Location behind the interplanetary magnetic field (IMF) tangent surface to the bow shock and rotational symmetry around the solar wind flow (X) axis are the only presuppositions. The SFC system has been applied to over 300 observations of the boundary of the ULF compressional waves recorded by ISEE 1's magnetometer in 1978 and 1979. The boundary locations form a coherent pattern in the SFC frame. A selection of those cases for which the cone angle of the IMF was between 40 and 50 deg, corresponding to the average stream angle, yields a least square line whose mapping back to the solar ecliptic coordinates frame has slope of about 85 deg, very close to that of the tangent ULF boundary deduced earlier from more primitive methods with entirely different data sets. The line, being parallel to neither the IMF, the typical reflected beam, nor the shock, cannot be compatible with any model of wave production by beam-solar wind interaction that depends on uniform beam distribution or fixed growth rate. Rather, its tangency suggests the influence of a separate, escaping ion population.

Greenstadt, E. W.↗
NASA NTRS1984

Magnetic structure of the distant geotail from -60 to -220 earth radii - ISEE-3

ISEE-3 magnetic-field measurements in the region of the geomagnetic tail from -80 to -220 earth radii are reported and discussed. A well-ordered field structure is found, comprising two 7-8-nT lobes separated by a plasma sheet, an embedded neutral sheet with significant By fields, and an intermittent plasma-sheet boundary layer with 5-nT-amplitude (peak-to-peak) electromagnetic waves. The plasma-sheet Bz distribution changes from principally northern orientation near the earth to an approximately equal north-south distribution at 200-220 earth radii. These findings are considered to be in general agreement with magnetic-reconnection models of the magnetosphere, with reconnection either throughout the region observed (in tearing-mode or plasmoid-formation models) or at a constant (about 220-earth-radii) or variable (40-80 to 220-earth-radii) X line (in X-line models).

Tsurutani, B. T.↗
NASA NTRS2001

Creation and utilization of a World Wide Web based space radiation effects code: SIREST

In order for humans and electronics to fully and safely operate in the space environment, codes like HZETRN (High Charge and Energy Transport) must be included in any designer's toolbox for design evaluation with respect to radiation damage. Currently, spacecraft designers do not have easy access to accurate radiation codes like HZETRN to evaluate their design for radiation effects on humans and electronics. Today, the World Wide Web is sophisticated enough to support the entire HZETRN code and all of the associated pre and post processing tools. This package is called SIREST (Space Ionizing Radiation Effects and Shielding Tools). There are many advantages to SIREST. The most important advantage is the instant update capability of the web. Another major advantage is the modularity that the web imposes on the code. Right now, the major disadvantage of SIREST will be its modularity inside the designer's system. This mostly comes from the fact that a consistent interface between the designer and the computer system to evaluate the design is incomplete. This, however, is to be solved in the Intelligent Synthesis Environment (ISE) program currently being funded by NASA.

NASA Discipline Radiation Health↗
NASA NTRS1986

A statistical study of plasma sheet dynamics using ISEE 1 and 2 energetic particle flux data

Plasma sheet dynamics during substorms are studied by analyzing 461 cases of transient dropout events of the 1.5 and 6-keV particle fluxes detected by ISEE 1 and 2 satellites. The instruments for detecting low- and high-energy particles are described. The spatial distribution of flux dropout events, and the events' relationship to magnetospheric activity level are examined. Substorm events without observed flux dropout events are investigated. The data reveal that the flux dropout distribution is isotropic, between 12-23 earth radii, and is present in the entire nightside plasma sheet; and the substorms without flux dropout are more frequent near earth and magnetospheric flanks. It is observed that tailward of 12 earth radii the flux dropout events and substorms without flux dropout are similar. The Chao et al. (1977) MHD rarefaction wave propagation model and the Hones (1973, 1980) near-tail, X-type magnetic neutral line formation model are discussed and compared to the experimental data. It is noted that neither model explains the plasma sheet dynamics observed.

Dandouras, J.↗
NASA NTRS1996

Occurrency frequency of substorm field and plasma signatures observed near-earth by ISEE-1/2

The onset of the majority of substorms occurs when the tail field stops growing more tail-like and begins to become more dipolar. This corresponds to the onset signatures on the ground and in geosynchronous orbit. The AE indices and the IGS Pi 2 data were used to determine the major substorm onsets of 1978 and 1979. The time delay between successive substorms, the distribution of the substorm growth phase duration and the probability of tailward flows were determined as a function of spacecraft location. About a half of the substorms exhibit a plasma signature including earthward or tailward flows or plasma sheet drop out and recovery. Earthward flows are often seen at substorm onset, and almost always during substorm recovery. Tailward flows are occasionally seen at onset as the spacecraft is close enough to the neutral sheet. The experimental results are compared to predictions based on the neutral line and current sheet disruption models.

Hsu, T. S.↗
NASA NTRS1992

A determination of twisting of the Earth's magnetotail at distances 115-220 RE - ISEE 3

Observations from magnetic field and plasma experiments on ISEE 3 are used to identify and to analyze 16 crossings of the distant magnetotail neutral sheet. Four methods of analyses have been employed to measure the extent of the magnetotail twisting, which is found to be much greater than what was previously observed or, the theoretically inferred twist. A twist of more than 90 deg has frequently been observed on both open and closed magnetic field lines. In addition, the location of the magnetic neutral line of the magnetotail has been found to move over the distance interval of 115 to 220 Earth radii. Some features of these results suggest that a modification of the present solar wind-geomagnetic field interaction model may be needed.

Macwan, Snehavadan E.↗
NASA NTRS1983

New observations of plasma vortices and insights into their interpretation

Two- and three-dimensional plasma measurements and three-dimensional magnetic field measurements made with the ISEE 1 and 2 satellites during sixteen plasma vortex occurrences in the magnetotail plasma sheet are used to develop a fuller description of the vortex phenomenon than has existed heretofore. The phase and energy propagation properties of the vortex waves was studied in particular. The rotation period of the vortices (T = 10 + or - 5 minutes) is apparently independent of location, while the wavelength (lambda not less than several Re) increases with increasing distance down the tail, pointing to a global mode of propagation in which effects of inhomogeneous equilibrium are important. The flow rotation can be explained by propagation of surface waves or resonant waves in a uniform medium. Other observed features, however, require a nonuniform model: nonuniform propagation properties and differences of the phase propagation speed calculated from different components of velocity or magnetic field.

Hones, E. W., Jr.↗
NASA NTRS1986

Neutral sheet crossings by ISEE-3 in the distant magnetotail

Magnetic field data from ISEE-3 in the distant magnetotail at crossings of the field reversal (or neutral sheet) region were analyzed to determine the instantaneous direction of the normal component Bz at the crossing. A crossing identified as being almost always tailward of the steady-state X-line was selected. Data for 1 hr are discussed to illustrate difficulties. One particular smooth crossing shows that complicated microstructure can occur in times less than 1 min. Averaging over long times may eliminate essential information. Inspection of the magnetic field data at the highest resolution, however, shows that the direction of the plasma sheet flows and the sense of Bz across the neutral sheet do not always agree with the reconnection models. Rather, they indicate that the low latitude boundary layer may play a significant role in the dynamics of the magnetotail.

Heikkila, W. J.↗
NASA NTRS1984

Correlation between proton anisotropy and magnetic field direction in the distant geotail

A statistical analysis has been conducted of the anisotropy of suprathermal protons and the polarity of the magnetic field during April 10-16, 1983. At this time, ISEE-3 was at lunar distances in the geomagnetic tail of the earth, and well within the nominal magnetopause. The first-order anisotropy is presently correlated with the latitude angle and the z-component of the magnetic field. The anisotropy direction's frequency distribution is strongly peaked in the earthward and tailward direction, indicating fast earthward and tailward flows. For large anisotropies, and within 5 earth radii of the nominal neutral sheet position, a strong correlation is found between the earthward-streaming suprathermal protons and the northward polarity of the magnetic field; large tailward anisotropies are generally correlated with southward magnetic field polarity. This correlation is most simply interpreted in terms of a neutral line or reconnection model.

Klecker, B.↗
NASA NTRS1984

Comparison of solar flare X-ray producing and escaping electrons from about 2 to 100 keV

Using observations from the ISEE-3 spacecraft, the X-ray producing electrons and escaping electons from a solar flare on November 8, 1978 are compared. The instantaneous 5 to 75 keV electron spectrum in the X-ray producing region is computed from the observed bremsstrahlung X-ray spectrum. Assuming that energy loss by Coulomb collisions (thick target) is the dominant electron loss process, the accelerated electron spectrum is obtained. The energy spectrum of the escaping electrons observed from 2 to 100 keV differs significantly from the spectra of the X-ray producing electrons and of the accelerated electrons, even when the energy loss which the escaping electrons experienced during their travel from the sun to the earth is taken into account. The observations are consistent with a model where the escaping electons come from an extended X-ray producing region, which ranges from the chromosphere to high in the corona. In this model, the low energy escaping electrons (2-10 keV) come from the higher part of the extended X-ray source where the overlying column density is low, while the high energy electrons (20-100 keV) come from the entire X-ray source.

Pan, L.-D.↗
NASA NTRS1993

Anomalous aspects of magnetosheath flow and of the shape and oscillations of the magnetopause during an interval of strongly northward interplanetary magnetic field

On February 15, 1978, the orientation of the IMF remained steadily northward for more than 12 hours. Using plasma and magnetic field data from ISEE 1 and 2, IMP 8, and IMP 7, we show that (1) the magnetosheath flow speed on the flanks of the magnetotail steadily exceeded the solar wind speed by 20 percent, (2) surface waves of about 5-min period and very nonsinusoidal waveform were persistently present on the dawn magnetopause and waves of similar period were present in the dusk magnetosheath, and (3) the magnetotail ceased to flare at an antisunward distance of 15 earth radii. We propose that the acceleration of the magnetosheath flow is achieved by magnetic tension in the draped field configuration for northward IMP; the reduction of tail flaring is consistent with a decreased amount of open magnetic flux and a larger standoff distance of the subsolar magnetopause. Results of a 3D MHD simulation support this phenomenological model.

Chen, Sheng-Hsien↗
NASA NTRS1986

The heating of the thermal plasma with energetic electrons in small solar flares

The energetic electrons deduced from hard X-rays in the thick target model may be responsible for heating of soft X-ray plasma in solar flares. It is shown from OSO-7 studies that if a cutoff of 10 keV is assumed, the total electron is comparable to the thermal plasma energy. However, (1) the soft X-ray emission often appears to begin before the hard X-ray burst, (2) in about one-third of flares there is no detectable hard X-ray emission, and (3) for most events the energy content (assuming constant density) of soft X-ray plasma continues to rise after the end of the hard X-ray burst. To understand these problems we have analyzed the temporal relationship between soft X-rays and hard X-rays for 20 small events observed by ISEE-3 during 1980. One example is shown. The start of soft X-ray and hard X-ray bursts is defined as the time when the counting rates of the 4.8 to 5. keV and 25.8 to 43.2 keV channels, respectively, exceed the background by one standard deviation.

Lin, H. A.↗
NASA NTRS1994

Imaging the effect of dipole tilt on magetotail boundaries

Eight years of Interplanetary Monitoring Platform (IMP) 8, four years of International Sun Earth Explorer (ISEE) 2, and one year of IMP 7 magnetometer data have been combined to produce an 'image' of the average magnetic field for a YZ cross section (aberrated GSM) of the magnetotail at a downtail distance of 25 R(sub E). The shape of the neutral sheet and magnetopause boundaries can be observed directly from the images. A fitting function that qualitatively matches the observed boundary shape can then be chosen. This approach improves on previous fits to possible unsuitable functional forms specified independently of the data. In addition, as a refinement of previous studies, we have corrected for varying solar wind dynamic pressure and the effects of tail flaring. We find the magnetopause is displaced above the XY plane with increasing dipole tilt. The neutral sheet is found to curve slightly more than the model of Fairlfield (1980) during times of large dipole tilt and near the flanks appears to differ substantially from the neutral sheet shape given by the analytic model of Voigt (1984), the more recent neutral sheet model of Dandouras (1988) based on the Voigt model, and the semi-empirical model of Tsyganenko (1989).

Hammond, C. Max↗
NASA NTRS1993

Comment on 'Observations of reconnection of interplanetary and lobe magnetic field lines at the high-latitude magnetopause' by J.T. Gosling, M.F. Thomsen, S.J. Bame, R.C. Elphic, and C.T. Russell

Comment is presented on the results of measurements, reported by Gosling et al. (1991), that were made on ISEE in the vicinity of the high-latitude dusk magnetopause near the terminator plane, at a time when the local magnetosheath and tail lobe magnetic fields were nearly oppositely directed. The character of the observed plasma flowing both tailward and sunward within the high-latitude magnetopause current layer presented real evidence for the local reconnection process. Gosling et al. argued that this process may be a manifestation of different global magnetospheric topology structures. In the comment, a global magnetospheric convection pattern is constructed for the northward IMF and for the case of a large azimuthal component of the IMF with small Bz, irrespective of its sign. The suggested scheme provides a simple explanation for the observed sunward convection in the polar caps both for the northward and for strong By with small Bz. According to the present model, for the magnetosheath field at 2300 UT on June 11, 1978, the reconnection between the open field lines appears at the northern neutral point.

Belen'kaia, Elena↗
NASA NTRS1994

A detailed examination of a X-line region in the distant tail: ISEE-3 observations of jet flow and B(sub z) reversals and a pair of slow shocks

We report an observation of Petschek-type magnetic reconnection at a distant neutral line (X = -230 R(sub e)) with a full set of signatures of the magnetic merging process. These features include a reversal of plasma flows from earthward to tailward, a pair of slow shocks and the magnetic field X-type line. These two slow shocks are shown to satisfy the shock criteria used by Feldman et al. (1987). The spacecraft first crosses a slow shock to enter the earthward flowing plasmasheet with velocity of about 440 km/s. The embedded magnetic field has a positive B(sub z) component. The spacecraft next enters a region of tailward plasma flow with speed approximately 670 km/s and an embedded negative B(sub z), indicating entry into the plasmasheet tailward of the X-line. These observed velocities are comparable to calculated velocities based on Rankine-Hugoniot conservation relationships. The spacecraft subsequently returns into the south tail lobe by crossing another slow shock. Coplanarity analyses shows that the two slow shocks have orientations consistent with that predicted by the Petschek reconnection model. We note that this event occurs during northward interplanetary magnetic fields. Thus, a magnetic stress built-up in the distant tail may be responsible for this reconnection process.

Ho, C. M.↗
NASA NTRS1984

Plasmasheet magnetic fields in the distant tail

Data from two deep passes of ISEE-3 through the earth's magnetotail are used to discuss the evolution of the plasmasheet magnetic field as a function of radial distance and geomagnetic activity (Kp). Attention is focused on plasmasheet intervals lasting at least 10 min as recorded during passes lasting 3 and 5 mos with apogees of 221 and 238 earth radii (ER). The dependencies of the By and Bz components on Kp were minimal, although Bz displayed a radial dependence. No relationship was observed between By and Bz. The Bz component changed from a northward orientation at 60-100 ER to a N-S dependence at 200-238 ER. Variations in field measurements indicated turbulence throughout the plasmasheet, also independent of Kp. The data support formation of a plasmoid during periods of high Kp, and can serve as limiting conditions for developing more accurate magnetotail models.

Tsurutani, B. T.↗