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Results for “INTERPLANETARY MAGNETIC FIELD”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 487 records · Page 27
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NASA NTRS1985

A simple model for polar cap convection patterns and generation of theta auroras

An addition of the uniform interplanetary magnetic field and the earth's dipole magnetic field is used to evaluate electric field convection patterns over the polar caps that result from solar wind flow across open geomagnetic field lines. The model also accounts for field-aligned patterns within, and auroral arcs across, the polar cap. The qualitative predictions derived from the model express the electric field magnitudes, aurora intensity, sunward and antisunward flow, and the dusk-side reversal of the convection field in terms of the x and y components of the interplanetary magnetic field.

Lyons, L. R.↗
NASA NTRS2003

Structure of the Outer Cusp and Sources of the Cusp Precipitation during Intervals of a Horizontal IMF

The cusp represents a place where the magnetosheath plasma can directly penetrate into the magnetosphere. Since the main transport processes are connected with merging of the interplanetary and magnetospheric field lines: the interplanetary magnetic field (IMF) Orientation plays a decisive role in the formation of the high-altitude cusp. The importance of the sign of the IMF B(sub Z) component for this process was suggested about 40 years ago and later it was documented by many experimental investigations. However, situations when IMF Bz is the major IMF component are rather rare. The structure of the cusp during periods of a small IMF B(sub Z) is generally unknown, probably due to the fully 3-D nature of the interaction. The present case study reveals the importance of horizontal IMF components on the global magnetospheric configuration as well as on small-scale processes at the cusp-magnetosheath interface. We have used simultaneous measurements of several spacecraft (ISTP program) operating in different regions of interplanetary space and two closely spaced satellites (INTERBALL-1/MAGION-4) crossing the cusp-magnetosheath boundary to show the connection between the short- and large-scale phenomena. In the northern hemisphere, observations suggest a presence of two spots of cusp-like precipitation supplied by reconnection occurring simultaneously in both hemispheres. A source of this bifurcation is the positive IMF B(sub y) component further enhanced by the field draping in the magnetosheath. This magnetic field component shifts the entry point far away from the local noon but in opposite sense in either hemisphere. The cusp represents a place where the magnetosheath plasma can directly

Berchem, Jean↗
NASA NTRS1983

The structure of the heliospheric current sheet - 1978-1982

Continuing the study near solar minimum in 1976-1977 (Hoeksema et al., 1982), the configuration of the heliospheric magnetic field for the period 1976-1982 is calculated using a potential field model. Particular attention is given to the structure during the rising phase, maximum, and early decline of sunspot cycle 21, from 1978 to 1982. Four warps in the current sheet (the boundary between interplanetary magnetic field toward and away from the sun) are seen early in this interval; these give rise to a four-sector structure in the interplanetary magnetic field observed at earth. It is noted that the location of the current sheet changes slowly and extends to a heliographic latitude of approximately 50 deg. The strength of the polar field correction throughout this period is determined and included in the model calculations. The lower latitude magnetic fields become much stronger as the polar fields weaken and reverse polarity near maximum, decreasing the effect of the polar field correction.

Hoeksema, J. T.↗
NASA NTRS1974

Average high latitude magnetic field - Variation with interplanetary sector and with season. II

Average high-latitude magnetic-field data from northern observatories are examined for three ranges of magnetic disturbance level, Kp = 1- to 1+, 2- to 3+ and greater than or equal to 4-. Except for 0 to 0800 hr MLT, 55 to 78 deg invariant latitude, during away interplanetary magnetic field sectors, the variations between season and sector have the same characteristics at all Kp ranges. Because the amplitude of sector differences is much larger at sunlit local times than in the midnight sector, it is concluded that the current system of Svalgaard (1973) is not adequate to describe the sector variations in magnetic disturbance. Other current systems are discussed briefly. The disturbance morphology and seasonal variation at all Kp levels confirms the results of previous studies which indicate that latitudinally broad current systems and nonionospheric sources are present in addition to latitudinally narrow electrojet currents.

Langel, R.↗
NASA NTRS1993

A study of an expanding interplanatary magnetic cloud and its interaction with the earth's magnetosphere - The interplanetary aspect

High time resolution interplanetary magnetic field and plasma measurements of an interplanetary magnetic cloud and its interaction with the earth's magnetosphere on January 14/15, 1988 are interpreted and discussed. It is argued that the data are consistent with the theoretical model of magnetic clouds as flux ropes of local straight cylindrical geometry. The data also suggest that this cloud is aligned with its axis in the ecliptic plane and pointing in the east-west direction. Evidence consisting of the intensity and directional distribution of energetic particle in the magnetic cloud argues in favor of the connectedness of the magnetic field lines to the sun's surface. The intensities of about 0.5 MeV ions is rapidly enhanced and the particles stream in a collimated beam along the magnetic field preferentially from the west of the sun. The particles travel form a flare site along the cloud magnetic field lines, which are thus presumably still attached to the sun.

Farrugia, C. J.↗
NASA NTRS1973

On the interplanetary shock waves associated with solar flares in the active region McMath no. 9740

The propagation pattern of shock waves emitted by solar flares which occured in the active region McMath No. 9740 during 23 October to 4 November 1968 is discussed. The solar flares were associated with type 2 and 4 radio bursts and with SSC geomagnetic storms. The flares and associated phenomena are summarized and the transmit times between the sun and the earth of the shock waves associated with the flares are shown. It is concluded that the interplanetary magnetic field controls the propagation of shock waves emitted by solar flares. It was also determined that the large scale configuration of the interplanetary magnetic field was not disturbed by the successive propagation of the shock waves.

Sakurai, K.↗
NASA NTRS1974

The aurora and the magnetosphere - The Chapman Memorial Lecture

Review of recent progress in magnetospheric physics, in particular, in understanding the magnetospheric substorm. It is shown that a number of magnetospheric phenomena can now be understood by viewing the solar wind-magnetosphere interaction as an MHD dynamo; auroral phenomena are powered by the dynamo. Also, magnetospheric responses to variations of the north-south and east-west components of the interplanetary magnetic field have been identified. The magnetospheric substorm is entirely different from the responses of the magnetosphere to the southward component of the interplanetary magnetic field. It may be associated with the formation of a neutral line within the plasma sheet and with an enhanced reconnection along the line. A number of substorm-associated phenomena can be understood by noting that the new neutral line formation is caused by a short-circuiting of a part of the magnetotail current.

Akasofu, S.-I.↗
NASA NTRS1977

Observations of Jovian electrons at 1 AU throughout the 13 month Jovian synodic year

A study of Jovian electron-flux increases observed aboard the IMP-8 earth-orbiting satellite reveals that, contrary to previous reports of a 4-8-month Jovian electron 'season', Jovian electron-intensity increases were observed almost continuously from late 1973 into 1976, with peak intensities occurring at times of best connection between earth and Jupiter along the average direction of the interplanetary magnetic field about every 13 months. These observations are consistent with Jovian electron propagation both along and across the direction of the average interplanetary magnetic field. A convection-diffusion model for Jovian electron propagation, which assumes that Jupiter is a continuously emitting point source of electrons, originally developed to explain the distribution of Jovian electrons observed on the Pioneer 10 and 11 spacecraft, can account also for the distribution of Jovian electrons observed at the orbit of earth.

Chenette, D. L.↗
NASA NTRS1995

Solar wind eddies and the heliospheric current sheet

Ulysses has collected data between 1 and 5 AU during, and just following solar maximum, when the heliospheric current sheet (HCS) can be thought of as reaching its maximum tilt and being subject to the maximum amount of turbulence in the solar wind. The Ulysses solar wind plasma instrument measures the vector velocity and can be used to estimate the flow speed and direction in turbulent 'eddies' in the solar wind that are a fraction of an astronomical unit in size and last (have either a turnover or dynamical interaction time of) several hours to more than a day. Here, in a simple exercise, these solar wind eddies at the HCS are characterized using Ulysses data. This character is then used to define a model flow field with eddies that is imposed on an ideal HCS to estimate how the HCS will be deformed by the flow. This model inherently results in the complexity of the HCS increasing with heliocentric distance, but the result is a measure of the degree to which the observed change in complexity is a measure of the importance of solar wind flows in deforming the HCS. By comparison with randomly selected intervals not located on the HCS, it appears that eddies on the HCS are similar to those elsewhere at this time during the solar cycle, as is the resultant deformation of the interplanetary magnetic field (IMF). The IMF deformation is analogous to what is often termed the 'random walk' of interplanetary magnetic field lines.

Suess, S. T.↗
NASA NTRS1976

The generation of magnetic fields and electric currents in cometary plasma tails

Due to the folding of the interplanetary magnetic field into the tail as a comet sweeps through the interplanetary medium, the magnetic field in the tail can be built up to the order of 100 gammas at a heliocentric distance of about 1 AU. This folding of magnetic flux tubes also results in a cross-tail electric current passing through a neutral sheet. When streams of enhanced plasma density merge with the main tail, cross-tail currents as large as 1 billion A may result. A condition could arise which causes a significant fraction of this current to be discharged through the inner coma, resulting in rapid ionization. The typical time scale for such outbursts of ionization is estimated to be of the order of 10,000 sec, which is in reasonable agreement with observation.

Ip, W.-H.↗
NASA NTRS1989

Laboratory simulation of cometary neutral gas ionization

The laboratory simulation of the interaction of the solar wind with a comet is used to study the cometary neural gas ionization. The experiment is carried out in the UCR T-1 facility with an ice ball as the comet model. Photographs and data are taken with a variety of values of the solar wind velocity, interplanetary magnetic field (IMF), and comet configurations. The results show that the cometary neutral gas ionization depends on both the velocity of the solar wind and the interplanetary magnetic field. The plasma cloud surrounding the comet is visible only when the solar wind velocity and IMF are both above certain minimum values. This velocity dependent phenomena is explained by Alfven's critical ionization velocity effect. The critical magnetic field may be explained by assuming two stream lower hybrid instability as a triggering mechanism for the ionization of the neutral gas by plasma flow. Critical upper and lower limits for the magnetic field, required by anomalous ionization, are also derived that satisfy the experimental observations.

Chang, Tsuey-Fen↗
NASA NTRS1982

Electric fields measured by ISEE-1 within and near the neutral sheet during quiet and active times

An understanding of the physical processes occurring in the magnetotail and plasmasheet during different interplanetary magnetic field orientations and differing levels of ground magnetic activity is crucial for the development of a theory of energy transfer from the solar wind to the particles which produce auroral arcs. In the present investigation, the first observations of electric fields during neutral sheet crossings are presented, taking into account the statistical correlations of the interplanetary magnetic field direction and ground activity with the character of the electric field. The electric field data used in the study were obtained from a double probe experiment on the ISEE-1 satellite. The observations suggest that turbulent electric and magnetic fields are intimately related to plasma acceleration in the neutral sheet and to the processes which create auroral particles.

Cattell, C. A.↗
NASA NTRS1995

Synoptic maps of solar wind parameters from in situ spacecraft observations

Solar wind observations from the Interplanetary Monitoring Platform-8 (IMP-8) and Pioneer Venus Orbiter (PVO) spacecraft from 1982 until 1988 are combined to construct synoptic maps of solar wind parameters near 1 AU. Each map consists of 6 months of hourly averaged solar wind data, binned by heliographic latitude and Carrington longitude and projected back to the Sun. These maps show the structure and time evolution of solar wind streams near 1 AU in the heliographic latitudes of +/- 7.25 deg and provide and explicit picture of several phenomena, such as gradients, changes in the inclination of the heliospheric current sheet, and the relative positions of various structures in the inner heliosphere, that is difficult to obtain from single-spacecraft observations. The stream structure varied significantly during the last solar cycle. Between 1982 and early 1985, solar wind parameters did not depend strongly on heliographic latitude. During the last solar minimum, the solar wind developed significant latitudinal structure, and high-speed streams were excluded from the vicinity of the solar equator. The interplanetary magnetic field was strongly correlated with the coronal field, and the current sheet tended to coincide with the coronal neutral line. The solar wind speed showed the expected correlations with temperature, interplanetary magnetic field, and distance from the current sheet. The solar wind speed was anticorrelated with density, but the regions of highest density occurred east of the heliospheric current sheet and the regions of lowest solar wind speed. This is consistent with compression at the leading edge of high-speed streams.

Gazis, P. R.↗
NASA NTRS1977

Geomagnetic activity: Dependence on solar wind parameters

Current ideas about the interaction between the solar wind and the earth's magnetosphere are reviewed. The solar wind dynamic pressure as well as the influx of interplanetary magnetic field lines are both important for the generation of geomagnetic activity. The influence of the geometry of the situation as well as the variability of the interplanetary magnetic field are both found to be important factors. Semi-annual and universal time variations are discussed as well as the 22-year cycle in geomagnetic activity. All three are found to be explainable by the varying geometry of the interaction. Long term changes in geomagnetic activity are examined.

Svalgaard, L.↗
NASA NTRS1996

A Study of Uranus' Bow Shock Motions Using Langmuir Waves

During the Voyager 2 flyby of Uranus, strong electron plasma oscillations (Langmuir waves) were detected by the plasma wave instrument in the 1.78-kHz channel on January 23-24, 1986, prior to the inbound bow shock crossing. Langmuir waves are excited by energetic electrons streaming away from the bow shock. The goal of this work is to estimate the location and motion of Uranus' bow shock using Langmuir wave data, together with the spacecraft positions and the measured interplanetary magnetic field. The following three remote sensing analyses were performed: the basic remote sensing method, the lag time method, and the trace-back method. Because the interplanetary magnetic field was highly variable, the first analysis encountered difficulties in obtaining a realistic estimation of Uranus' bow shock motion. In the lag time method developed here, time lags due to the solar wind's finite convection speed are taken into account when calculating the shock's standoff distance. In the new trace-back method, limits on the standoff distance are obtained as a function of time by reconstructing electron paths. Most of the results produced by the latter two analyses are consistent with predictions based on the standard theoretical model and the measured solar wind plasma parameters. Differences between our calculations and the theoretical model are discussed.

Xue, S.↗
NASA NTRS1986

Magnetospheric origin of energetic (at least 50 keV) ions upstream of the bow shock - The October 31, 1977, event

Energetic particle data gathered by the ISEE-1 and IMP-7 and -8 spacecraft on Oct. 31, 1977 while travelling inside the plasma sheet upstream of the earth's bow shock are analyzed for an indication of the source of the 30 keV-1 MeV particles observed. The IMP spacecraft also travelled through the magnetosphere and the dawn bow shock during the measurement data. The data included records of magnetospheric bursts of energetic protons, which had intensities about 2-8 times higher inside the plasma sheet than did the proton intensities. The magnetospheric bursts began about 40 min before the ISEE recorded an upstream ion event and 2 hr before its cutoff. Other data indicated that the appearance of upstream ions was controlled by the interplanetary magnetic field. The ions arose in the plasma sheet of the magnetosphere and in 'leaking' upstream experienced a separation of ions from electrons, a condition caused by the interplanetary magnetic field. A phenomenological model is developed for the process of injection of energetic particles upstream of the bow shock in a manner that is not commensurate with Fermi acceleration.

Anagnostopoulos, G. C.↗