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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Heliomagnetic latitude dependence of the heliospheric magnetic field

Previous studies have revealed systematic variations of the interplanetary magnetic field with heliographic latitude. Luhmann et al. (1987) modeled Pioneer Venus (PVO) and ISEE-3 observations by assuming an asymmetric dependence on heliolatitude with stronger fields in the northern hemisphere. In a subsequent study, using data from ISEE-3/ICE and IMP-8, Burton et al. (1990) found evidence for a similar asymmetry. However, neither model has been completely successful. The model derived from PVO/ICE observations agrees quite well near solar maximum but shows significant discrepancies during the descending phase of the solar cycle. The model derived from the ICE/IMP-8 comparison suffers from significant phase delays between the difference in field magnitude at the two spacecraft and their latitude difference. In an attempt to account for these phase shifts, the IMP-8 and ICE data have been reexamined in heliomagnetic coordinates which are defined by the orientation of the solar magnetic dipole. The latitude and longitude of the dipole inferred from the data have then been compared with those implicit in source surface calculations. The IMP/ICE correlations have been extended into the recent solar maximum and descending phase. Comparisons have also been carried out between IMP-8 and Ulysses as it traveled to -30 deg south heliographic latitude.

Burton, M. E.↗
NASA NTRS1977

Sources of magnetic fields in recurrent interplanetary streams

The sources of magnetic fields in recurrent streams were examined. Most fields and plasmas at 1 AU were related to coronal holes, and the magnetic field lines were open in those holes. Some of the magnetic fields and plasmas were related to open field line regions on the sun which were not associated with known coronal holes, indicating that open field lines are more basic than coronal holes as sources of the solar wind. Magnetic field intensities in five equatorial coronal holes ranged from 2G to 18G. Average measured photospheric magnetic fields along the footprints of the corresponding unipolar fields on circular equatorial arcs at 2.5 solar radii had a similar range and average, but in two cases the intensities were approximately three times higher than the projected intensities. The coronal footprints of the sector boundaries on the source surface at 2.5 solar radii, meandered between -45 deg and +45 deg latitude, and their inclination ranged from near zero to near ninety degrees.

Burlaga, L. F.↗
NASA NTRS2011

An Assessment of the Length and Variability of Mercury's Magnetotail

We employ Mariner 10 measurements of the interplanetary magnetic field in the vicinity of Mercury to estimate the rate of magnetic reconnection between the interplanetary magnetic field and the Hermean magnetosphere. We derive a time-series of the open magnetic flux in Mercury's magnetosphere. from which we can deduce the length of the magnetotail The length of the magnetotail is shown to be highly variable. with open field lines stretching between 15R(sub H) and 8S0R(sub H) downstream of the planet (median 150R(sub H)). Scaling laws allow the tail length at perihelion to be deduced from the aphelion Mariner 10 observations.

Milan, S. E.↗
DOE OSTI2024

Review of the August 1972 and March 1989 (Allen) Space Weather Events: Can We Learn Anything New From Them?

Abstract Updated summaries of the August 1972 and March 1989 space weather events have been constructed. The features of these two events are compared to the Carrington 1859 event and a few other major space weather events. It is concluded that solar active regions release energy in a variety of forms (X‐rays, EUV photons, visible light, coronal mass ejection (CME) plasmas and fields) and they in turn can produce other energetic effects (solar energetic particles (SEPs), magnetic storms) in a variety of ways. It is clear that there is no strong one‐to‐one relationship between these various energy sinks. The energy is often distributed differently from one space weather event to the next. Concerning SEPs accelerated at interplanetary CME (ICME) shocks, it is concluded that the Fermi mechanism associated with quasi‐parallel shocks is relatively weak and that the gradient drift mechanism (electric fields) at quasi‐perpendicular shocks will produce harder spectra and higher fluxes. If the 4 August 1972 intrinsic magnetic cloud condition (southward interplanetary magnetic field instead of northward) and the interplanetary Sun to 1 au conditions were different, a 4 August 1972 magnetic storm and magnetospheric dawn‐to‐dusk electric fields substantially larger than the Carrington event would have occurred. Under these special interplanetary conditions, a Miyake et al. (2012), https://doi.org/10.1038/nature11123 ‐like extreme SEP event may have been formed. The long duration complex 1989 storm was probably greater than the Carrington storm in the sense that the total ring current particle energy was larger.

Tsurutani, Bruce T.↗
NASA NTRS1976

The causes of recurrent geomagnetic storms

The causes of recurrent geomagnetic activity were studied by analyzing interplanetary magnetic field and plasma data from earth-orbiting spacecraft in the interval from November 1973 to February 1974. This interval included the start of two long sequences of geomagnetic activity and two corresponding corotating interplanetary streams. In general, the geomagnetic activity was related to an electric field which was due to two factors: (1) the ordered, mesoscale pattern of the stream itself, and (2) random, smaller-scale fluctuations in the southward component of the interplanetary magnetic field Bz. The geomagnetic activity in each recurrent sequence consisted of two successive stages. The first stage was usually the most intense, and it occurred during the passage of the interaction region at the front of a stream. These large amplitudes of Bz were primarily produced in the interplanetary medium by compression of ambient fluctuations as the stream steepened in transit to 1 A.U. The second stage of geomagnetic activity immediately following the first was associated with the highest speeds in the stream.

Burlaga, L. F.↗
NASA NTRS1974

A comparison of the geomagnetic ap index with fluctuations in B and V - Mariner 5

Mariner 5 data for the interplanetary magnetic field and the solar wind velocity are compared with terrestrial ap values for the period from June 15, to August 22, 1967. It is concluded that fluctuations in the interplanetary magnetic field are more closely coupled to geomagnetic activity as measured with the ap index than are fluctuations in the solar wind velocity. During periods of high-level activity, the data support the Dessler and Walters (1964) model where the magnetic field is the primary causal agent of geomagnetic activity.

Jones, D. E.↗
NASA NTRS1981

What causes the warp in the heliospheric current sheet

A comparative discussion of the warp in the heliospheric current sheet is presented. Pioneer 10 and 11 data of the interplanetary magnetic field compared with earlier data (Helios 1 and 2) show a good agreement on the phenomenon of the warp; however, the interpretations differ. One theory (Thomas and Smith, 1980) proposes that fast solar wind streams associated with interaction regions may move the current sheet higher to heliospheric latitudes, thus causing the warp; while the earlier theory (1976) adequately explained the phenomenon by using the observed photospheric magnetic field and the Zeeman effect but omitted the solar wind dynamical considerations as part of the computations. It is shown that the Helios data of the polarity of the interplanetary magnetic field are in good agreement with the computed location of the current sheet, confirming the earlier theory.

Wilcox, J. M.↗
NASA NTRS1984

Dependence of the High Latitude Middle Atmosphere Ionization on Structures in Interplanetary Space

The precipitation of high energetic electrons during and after strong geomagnetic storms into heights below 100 km in middle and subauroral latitudes is markedly modulated by the structure of the interplanetary magnetic field (IMF). Under relative quiet conditions the D-region ionization caused by high energetic particle precipitation (energies greater than 20 to 50 keV) depends on changes of the interplanetary magnetic field and also on the velocity of the solar wind. To test this assumption, the influence of the IMF-sector boundary crossings on ionospheric absorption data of high and middle latitudes by the superposed-epoch method was investigated.

Bremer, J.↗
NASA NTRS1965

Magnetometer experiment

Mariner IV space probe magnetometer observations of interplanetary magnetic field transitions

MAGNETOMETER↗
NASA NTRS1990

Spacecraft observations of the interaction of active comets with the solar wind

Six spacecraft encountered two comets during 1985 and 1986, obtaining a wealth of data relative to the plasma processes at work in the interaction of an active comet with the solar wind. A review of what space plasma scientists have learned from these data and of their interpretations is presented. The interaction process begins millions of kilometers from the nucleus where the solar wind first picks up cometary ions that slow down the wind and causes the interplanetary magnetic field to pile up and drape around the comet's ionosphere. Thus the geometry of a comet's plasma tail is defined by this draped field. At Halley the Giotto spacecraft noted a well-defined boundary separating the mixture of solar wind and cometary plasmas and the interplanetary magnetic field from the free-field, almost pure cometary plasma in the inner coma. Additional unexpected features in the inner coma were a flux of fast 'granddaughter' ions and high densities of negative ions. Further details covering pickup ions and plasma waves, mass loading, bow shock, energetic particles, the cometosheath, the ionopause, the plasma tail, and the field-free region are provided.

Neugebauer, M.↗
NASA NTRS1992

Comment on 'Solar wind control of the magnetopause shape, location, and motion' by D. G. Sibeck, R. E. Lopez, and E. C. Roelof

The methodology employed in the paper 'Solar wind control of the magnetopause shape, location, and motion' by Sibeck et al. (1991), which quantifies the magnetospheric response to solar wind dynamic pressure and interplanetary magnetic field variations, is commented on, with emphasis on how the shape and position of the magnetopause boundary can be specified, within some uncertainty, for particular simultaneous values of the solar wind pressure in the magnetic field. The reply of Sibeck et al. included a data set of 1821 magnetopause crossings, each associated with an hourly averaged solar wind dynamic pressure and/or north-south component of the interplanetary magnetic field. A least squares fit to an ellipsoid of revolution to subsets of the data was performed.

Dunlop, M. W.↗
NASA NTRS1996

Magnetic Storms and Associated Interplanetary Phenomena

The physical mechanism for energy transfer from the solar wind to the magnetosphere is magnetic reconnection between the interplanetary field and the Earth's field. From Intro: It is the purpose of this paper to review the sources of such interplanetary magnetic fields distinguishing between the solar maximum and the declining phases of the solar cycle.

solar wind magnetosphere solar energy transfer cor↗
NASA NTRS1995

A case and statistical study of transient magnetic field events at geosynchronous orbit and their solar wind origin

We present a statisical survey of Prognoz 10 solar wind observations at the times of transient (step function and impulsive) variations in the dayside magnetospheric magnetic field strength measured by the GOES 5 and 6 geosynchronous satellites. The results indicate that 51% of the magnetospheric events can be associated with corresponding variations in the solar wind dynamic pressure. A further 17% of the events can be associated with fluctuations in the interplanetary magnetic field orientation in the sense previously associated with foreshock pressure pulses. We find no tendency for impulsive events at dayside geosynchronous orbit to be associated with north/south fluctuations in the interplanetary magnetic field (IMF) orientation, nor for the events to occur primarily during intervals of southward IMF. The success rate for associating transient events at dayside geosynchronous orbit with solar wind features decreases as Prognoz 10 moves farther from the Earth-Sun line. The observations indicate that variations in the solar wind dynamic pressure and foreshock pressure pulses associated with variations in the IMF cone angle are the predominant causes of large-amplitude transient events observed at dayside geosynchronous orbit.

Borodkova, N. L.↗
NASA NTRS1977

Triggering of substorms by solar wind discontinuities

The probability of triggering of polar substorms by a large-scale magnetospheric compression associated with a discontinuity in the solar wind has been examined statistically using ground magnetogram data, AE index data and satellite geomagnetic data on 125 sudden storm commencements observed during 1967-1970. The triggering probability was found to depend on the amplitude of the sudden storm commencement and on the degree of preceding AE activity. In almost all cases the triggering occurred when the B-Z component of the interplanetary magnetic field was negative or decreasing during the 30 min before the passage of the discontinuity. Transient geomagnetic responses with a time scale of Alfven wave propagation in the polar cap also depend on interplanetary magnetic field conditions.

Kokubun, S.↗
NASA NTRS1997

Evolution of the Global Aurora During Positive IMP Bz and Varying IMP By Conditions

The DE 1 imaging instrumentation provides a full view of the entire auroral oval every 12 min for several hours during each orbit. We examined five examples of global evolution of the aurora that occurred during the northern hemisphere winter of 1981-1982 when the z component of the interplanetary magnetic field was positive and the y component was changing sign. Evolution of an expanded auroral emission region into a theta aurora appears to require a change in the sign of By during northward interplanetary magnetic field (IMF). Theta aurora are formed both from expanded duskside emission regions (By changes from positive to negative) and dawnside emission regions (By changes from negative to positive), however the dawnside-originating and duskside-originating evolutions are not mirror images. The persistence of a theta aurora after its formation suggests that there may be no clear relationship between the theta aurora pattern and the instantaneous configuration of the IMF.

Cumnock, J. A.↗
NASA NTRS1985

The distant magnetotail

Satellite, balloon, aircraft, and ground-based data are presented for the night of February 24, 1974, when variations in the interplanetary magnetic field caused a series of small substorms. The data are interpreted as indicating that a series of small plasmoids were formed in the magnetotail, travelled tailward rubbing on closed field lines, and produced poleward travelling auroral features as the ionospheric footprint of the plasmoids. When the plasmoids cross the X-line and magnetopause onto interplanetary magnetic field lines they lose connection with the earth and the auroral features disappear. In this instance, the closed field line portion reached up to nearly 80 deg in geomagnetic latitude, over 10 deg poleward from the auroral oval.

Heikkila, W.↗
NASA NTRS1997

Evolution of the Global Aurora During Positive IMF B(sub z) and Varying IMF B(sub y) Conditions

The DE 1 imaging instrumentation provides a full view of the entire auroral oval every 12 min for several hours during each orbit. We examined five examples of global evolution of the aurora that occurred during the northern hemisphere winter of 1981-1982 when the z component of the interplanetary magnetic field (IMF) was positive and the y component was changing sign. Evolution of an expanded auroral emission region into a theta aurora appears to require a change in the sign of B(sub y) during northward Interplanetary Magnetic Field. Theta aurora are formed both from expanded duskside emission regions (B(sub y) changes from positive to negative) and dawnside emission regions (B(sub y) changes from negative to positive), however the dawnside-originating and duskside-originating evolutions are not mirror images. The persistence of a theta aurora after its formation suggests that there may be no clear relationship between the theta aurora pattern and the instantaneous configuration of the IMF.

Cumnock, J. A.↗