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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Simulation of interplanetary magnetic field B{sub y} penetration into the magnetotail

Based on our global 3D magnetospheric MHD simulation model, we investigate the phenomena and physical mechanism of the B{sub y} component of the interplanetary magnetic field (IMF) penetrating into the magnetotail. We find that the dayside reconnected magnetic field lines move to the magnetotail, get added to the lobe fields, and are dragged in the IMF direction. However, the B{sub y} component in the plasma sheet mainly originates from the tilt and relative slippage of the south and north lobes caused by plasma convection, which results in the original B{sub z} component in the plasma sheet rotating into a B{sub y} component. Our research also shows that the penetration effect of plasma sheet B{sub y} from the IMF B{sub y} during periods of northward IMF is larger than that during periods of southward IMF.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1974

The spiral interplanetary magnetic field: A polarity and sunspot cycle variation

Spacecraft observations near the earth of the yearly average direction of the interplanetary magnetic field during the sunspot maximum year 1968 showed a deviation from the spiral field. The angle between the average field direction when the field polarity was away from the sun and the average direction for toward polarity was 168 deg, rather than 180 deg. This effect appears to have a sunspot cycle variation.

Svalgaard, L.↗
NASA NTRS2012

Turbulence in a Global Magnetohydrodynamic Simulation of the Earth's Magnetosphere during Northward and Southward Interplanetary Magnetic Field

We report the results of MHD simulations of Earth's magnetosphere for idealized steady solar wind plasma and interplanetary magnetic field (IMF) conditions. The simulations feature purely northward and southward magnetic fields and were designed to study turbulence in the magnetotail plasma sheet. We found that the power spectral densities (PSDs) for both northward and southward IMF had the characteristics of turbulent flow. In both cases, the PSDs showed the three scale ranges expected from theory: the energy-containing scale, the inertial range, and the dissipative range. The results were generally consistent with in-situ observations and theoretical predictions. While the two cases studied, northward and southward IMF, had some similar characteristics, there were significant differences as well. For southward IMF, localized reconnection was the main energy source for the turbulence. For northward IMF, remnant reconnection contributed to driving the turbulence. Boundary waves may also have contributed. In both cases, the PSD slopes had spatial distributions in the dissipative range that reflected the pattern of resistive dissipation. For southward IMF there was a trend toward steeper slopes in the dissipative range with distance down the tail. For northward IMF there was a marked dusk-dawn asymmetry with steeper slopes on the dusk side of the tail. The inertial scale PSDs had a dusk-dawn symmetry during the northward IMF interval with steeper slopes on the dawn side. This asymmetry was not found in the distribution of inertial range slopes for southward IMF. The inertial range PSD slopes were clustered around values close to the theoretical expectation for both northward and southward IMF. In the dissipative range, however, the slopes were broadly distributed and the median values were significantly different, consistent with a different distribution of resistivity.

magnetohydrodynamics (MHD)↗
NASA NTRS1975

Enhanced interplanetary magnetic fields as the cause of Forbush decreases

A strong correlation is observed between neutron monitor variations and variations in the interplanetary magnetic field intensity. It is thought that the cosmic ray intensity depressions are caused by perpendicular gradient drifts. The perpendicular gradient drift velocity for particles with energies exceeding 500 MeV in a magnetic field configuration produced by a representative stream is at least a few times the solar wind velocity. Thus particles can be swept away from the ecliptic by such a blob faster than the blob advances. It is suggested that this mechanism might be the cause of Forbush decreases and other cosmic ray variations near 1 AU.

Burlaga, L. F.↗
NASA NTRS1977

The response of the dayside aurora to sharp northward and southward transitions of the interplanetary magnetic field and to magnetospheric substorms

Latitudinal shifts of the discrete dayside aurora are examined with respect to variations in the interplanetary magnetic field (IMF) and to magnetospheric substorms. Within 10-15 min after steplike southward (northward) transitions in the IMF the dayside auroral oval moves equatorward (poleward). In at least some cases the auroral shift is similar to an exponential relaxation in latitude from an initial to a final steady state value; for these cases the average exponential time constant is estimated to be 17 min. Substorm features in the dayside aurora include (1) an equatorward shift by 1-3 deg of the equatorward discrete auroral boundary, (2) a brightening of the discrete aurora near substorm onset, (3) the formation of multiple auroral bands, and (4) poleward motion of short-lived individual auroral arcs occurring nearly coincident in time with the equatorward boundary shifts, the average poleward velocity of these arcs being approximately 800 m/s.

Horwitz, J. L.↗
NASA NTRS1978

Heliocentric distance dependence of the interplanetary magnetic field

Numerous spacecraft measurements bearing on the heliocentric distance dependencies of both large- and small-scale properties of the interplanetary magnetic field (IMF) are assembled and compared. These data tend to indicate that the average of the radial field component varies as the inverse square of distance. However, the azimuthal component is rather strongly a function of time, being influenced by both the time-dependent solar wind speed and the evolution of the source field at the sun. Thus, unless the solar wind speed dependence is taken into account, individual sets of measurements by a single spacecraft give an azimuthal component gradient which is steeper than the inverse distance dependence predicted from the Parker spiral model. A least squares fit to the composite (five spacecraft) solar rotation average data set gives a result close to the inverse distance dependence. Preliminary Helios results suggest general consistency with the spiral model.

Behannon, K. W.↗
NASA NTRS1978

The large-scale structure of the interplanetary magnetic field between 1 and 0.3 AU during the primary mission of Helios 1

The macroscale and mesoscale structure of the interplanetary magnetic field during the primary mission of Helios 1 is discussed. The radial field component behaves essentially in agreement with Parker's theory. The transverse component shows a larger variability than the radial component; its radial variation is in good agreement with Parker's theory for high speeds, but some deviation is found for low speeds. The radial variation of the field variance is also studied. Its dependence upon the heliocentric distance r is expressed by the law 1/r cubed, which is necessary but not sufficient for Alfven waves. The available data do not allow a unique interpretation of the 1/r cubed dependence. No big differences are observed between low (less than or equal to 500 km/s) and high (greater than or equal to 600 km/s) solar wind velocity regimes.

Mariani, F.↗
NASA NTRS1981

Large-scale variations of the interplanetary magnetic field: Voyager 1 and 2 observations between 1-5 AU

Observations by the Voyager 1 and 2 spacecraft of the interplanetary magnetic field between 1 and 5 AU were used to investigate the large scale structure of the IMF in a period of increasing solar activity. The Voyager spacecraft found notable deviations from the Parker axial model. These deviations are attributed both to temporal variations associated with increasing solar activity, and to the effects of fluctuations of the field in the radial direction. The amplitude of the latter fluctuations were found to be large relative to the magnitude of the radial field component itself beyond approximately 3 AU. Both Voyager 1 and Voyager 2 observed decreases with increasing heliocentric distance in the amplitude of transverse fluctuations in the averaged field strength (B) which are consistent with the presence of predominantly undamped Alfven waves in the solar wind, although and necessarily implying the presence of them. Fluctuations in the strength of B (relative to mean field strength) were found to be small in amplitude, with a RMS which is approximately one third of that for the transverse fluctuations and they are essentially independent of distance from the Sun.

Burlaga, L. F.↗
NASA NTRS1995

The regular interplanetary magnetic field during the 1980s

The regular magnetic field in the interplanetary space for 1980-1990 is calculated using the results of the Hoeksema-Zhao model for the radial magnetic field on the source surface. The unsteady radial component gives birth to the latitudinal and longitudinal components which could be of importance for, e.g., the galactic cosmic ray modulation.

Kalinin, M. S.↗
NASA NTRS1982

Dawn-dusk asymmetry of the tail region of the magnetosphere of Saturn and the interplanetary magnetic field

In connection with the findings of the Voyager 1 mission, it appears that the tail lobe of Saturn is very different from that of earth and Jupiter, in that the latter are devoid of energetic particles, and magnetic field lines in this region are thought to be open and interconnecting with the interplanetary magnetic field at large distances in the antisolar direction. The present investigation is concerned with a possible explanation of these observations, taking into account a model of Saturn's magnetosphere. It is shown that the Voyager 1 spacecraft remained in the closed region of the magnetotail during its entire tail traversal and did not have an opportunity to penetrate into the high latitude lobe. It is concluded that Saturn probably has a tail lobe just like earth and Jupiter. However, this tail lobe was not traversed by Voyager.

Akasofu, S.-I.↗
NASA NTRS1992

Small-scale electrodynamics of the cusp with northward interplanetary magnetic field

Possible low-altitude field signatures of merging occurring at high latitudes during a period of strong northward directed interplanetary magnetic field are reported. Large electric and magnetic field spikes detected at the poleward edge of the magnetosheathlike particle precipitation are interpreted as field signatures of the low-altitude footprint of such merging line locations. A train of phase-shifted, almost linearly polarized electric and magnetic field fluctuations was detected just equatorward of the large electromagnetic spike. It is argued that these may be due to either ion cyclotron waves excited by penetrating magnetosheath ions or transient oscillations in the frame of convecting plasma, brought about by the sudden change in the flow at the magnetospheric end of the field line.

Basinska, Ewa M.↗
NASA NTRS2011

Interplanetary Magnetic Field Guiding Relativistic Particles

The origin and the propagation of relativistic solar particles (0.5 to few Ge V) in the interplanetary medium remains a debated topic. These relativistic particles, detected at the Earth by neutron monitors have been previously accelerated close to the Sun and are guided by the interplanetary magnetic field (IMF) lines, connecting the acceleration site and the Earth. Usually, the nominal Parker spiral is considered for ensuring the magnetic connection to the Earth. However, in most GLEs the IMF is highly disturbed, and the active regions associated to the GLEs are not always located close to the solar footprint of the nominal Parker spiral. A possible explanation is that relativistic particles are propagating in transient magnetic structures, such as Interplanetary Coronal Mass Ejections (ICMEs). In order to check this interpretation, we studied in detail the interplanetary medium where the particles propagate for 10 GLEs of the last solar cycle. Using the magnetic field and the plasma parameter measurements (ACE/MAG and ACE/SWEPAM), we found widely different IMF configurations. In an independent approach we develop and apply an improved method of the velocity dispersion analysis to energetic protons measured by SoHO/ERNE. We determined the effective path length and the solar release time of protons from these data and also combined them with the neutron monitor data. We found that in most of the GLEs, protons propagate in transient magnetic structures. Moreover, the comparison between the interplanetary magnetic structure and the interplanetary length suggest that the timing of particle arrival at Earth is dominantly determined by the type of IMF in which high energetic particles are propagating. Finally we find that these energetic protons are not significantly scattered during their transport to Earth.

Masson, S.↗
NASA NTRS1973

Cross-correlation analysis of the AE index and the interplanetary magnetic field Bz component.

A cross-correlation study between magnetospheric activity (the AE index) and the southward-directed component of the interplanetary magnetic field (IMF) is made for a total of 792 hours (33 days) with a time resolution of about 5.5 min. The peak correlation tends to occur when the interplanetary data are shifted approximately 40 min later with respect to the AE index data. Cross-correlation analysis is conducted on some idealized wave forms to illustrate that this delay between southward turning of the IMF and the AE index should not be interpreted as being the duration of the growth phase.

Meng, C.-I.↗
NASA NTRS1976

Influence of the interplanetary magnetic field on the occurrence and thickness of the plasma mantle

The response of the plasma mantle to the orientation of the interplanetary magnetic field (IMF) has been studied by correlating Heos 2 plasma and Imp 6 magnetic field data. The mantle is nearly always present when the IMF has a southward component and often also when the field has a weak northward component. In addition, the mantle appears increasingly thicker with greater southward components. On the other hand, the mantle is thin or missing (from the region where it is normally found) when the average IMF has a strong northward component. This result supports the idea that polar cap convection plays a dominant role in the formation of the plasma mantle: mantle plasma originates in the magnetosheath, enters the magnetosphere through the day side polar cusps, and is transported across the cusp to the night side by means of a convection electric field whose magnitude is controlled by the orientation of the IMF.

Sckopke, N.↗
NASA NTRS1979

An extended investigation of Helios 1 and 2 observations - The interplanetary magnetic field between 0.3 and 1 AU

Helios 1 and 2 spacecraft allowed a detailed investigation of the radial dependence of the interplanetary magnetic field components between 0.3 and 1 AU. The behavior of the radial component is in a very good agreement with Parker's model (approximately equal to the inverse square of the heliocentric distance) and the azimuthal component also shows a radial dependence which is close to theoretical predictions (approximately equal to the inverse of the heliocentric distance). Experimental results for the normal component and for the field magnitude are consistent with those from previous investigations. The relative amplitude of the directional fluctuations with periods less than 12 hr is essentially independent of heliocentric distance, while their power decreases approximately as the inverse cube of the heliocentric distance without any appreciable difference between higher and lower velocity regimes.

Mariani, F.↗
NASA NTRS2007

An Alternative Interpretation of the Relationship between the Inferred Open Solar Flux and the Interplanetary Magnetic Field

Photospheric observations at the Wilcox Solar Observatory (WSO) represent an uninterrupted data set of 32 years and are therefore unique for modeling variations in the magnetic structure of the corona and inner heliosphere over three solar cycles. For many years, modelers have applied a latitudinal correction factor to these data, believing that it provided a better estimate of the line-of-sight magnetic field. Its application was defended by arguing that the computed open flux matched observations of the interplanetary magnetic field (IMF) significantly better than the original WSO correction factor. However, no physically based argument could be made for its use. In this Letter we explore the implications of using the constant correction factor on the value and variation of the computed open solar flux and its relationship to the measured IMF. We find that it does not match the measured IMF at 1 AU except at and surrounding solar minimum. However, we argue that interplanetary coronal mass ejections (ICMEs) may provide sufficient additional magnetic flux to the extent that a remarkably good match is found between the sum of the computed open flux and inferred ICME flux and the measured flux at 1 AU. If further substantiated, the implications of this interpretation may be significant, including a better understanding of the structure and strength of the coronal field and I N providing constraints for theories of field line transport in the corona, the modulation of galactic cosmic rays, and even possibly terrestrial climate effects.

Riley, Pete↗
NASA NTRS1984

Large-scale interplanetary magnetic fields: Voyager 1 and 2 observations between 1 AU and 9.5 AU

The large-scale radial and temporal variations of the interplanetary magnetic field strength B observed by Voyagers 1 and 2 are discussed. Two components of the magnetic field strength were considered: (1) an average component, B sub zero, based on solar rotation averages, and (2) a fluctuation component, delta B, expressed by 10- or 24-hour averages of B normalized by the best-fit average field for the corresponding time and distance. Observations of the sector structure, interfaces, and shocks are presented to further describe magnetic field strength.

Burlaga, L. F.↗