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Spiro, R. W.

Publications and source records attributed to Spiro, R. W..

33 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

The role of the auroral ionosphere in magnetospheric substorms

It is pointed out that the energy which is released during a magnetospheric substorm has large and obvious effects on the earth's auroral ionosphere. The present investigation is concerned with the question of the effect of the ionosphere on substorm phenomena which occur near the magnetospheric equatorial plane. Plasma transfer between ionosphere and magnetosphere are discussed along with general theoretical considerations regarding magnetospheric currents, plasma sheet dynamics, and ring current injection. Attention is given to questions concerning the occurrence of substorms, ion circulation in the magnetospheric convection cycle, time-dependent plasma ejection from plasma-sheet flux tubes, and a schematic of the magnetospheric-convection current circuit.

Wolf, R. A.↗
NASA NTRS1982

Precipitating electron energy flux and auroral zone conductances - An empirical model

Data from the low energy electron (LEE) experiments on the Atmosphere Explorer C and D satellites have been used to determine the average global distribution of the energy flux of precipitating auroral electrons and their average energy for different levels of geomagnetic activity. Measurements from the Atmosphere Explorer unified abstract file (15-s resolution) have been binned according to invariant latitude (in the range 50-90 deg), magnetic local time, and geomagnetic activity as measured by the Kp and auroral electrojet (AE) indices, separately. Bin-averaged values of precipitating energy flux and average energy have been calculated, and a smoothing algorithm used to reduce stochastic variations in the raw data. The results indicate that, for the parameters studied, the AE inces does a superior job of ordering the data with regard to geomagnetic activity. The global distribution of the auroral enhancement porition of the Pedersen and Hall conductances were inferred from the data by means of an empirical fit to detailed energy deposition calculations.

Spiro, R. W.↗
NASA NTRS1982

Computer simulation of inner magnetospheric dynamics for the magnetic storm of July 29, 1977

The Rice University convection model is applied to the early main phase of the July 29, 1977 magnetic storm through a computer implementation that self-consistently calculates electric fields, currents, and plasma distributions and velocities in the inner magnetosphere/ionosphere system. On the basis of solar wind parameters and AL index as inputs, the model predicts the injection of plasma sheet plasma to form a substantial storm time ring current whose total predicted strength agrees with the observed Dst index. The possibility that the magnetic field may be sufficiently inflated to make 60 deg field lines extend to the outer magnetosphere is examined. In the model, distortion of the plasma sheet inner edge by magnetospheric compression associated with the sudden commencement temporarily disrupts the normal Birkeland current pattern. Normal Birkeland currents and shielding reassert themselves in about an hour.

Wolf, R. A.↗
NASA NTRS1982

A model of the high-latitude ionospheric convection pattern

Mathematical expressions have been constructed that allow the large-scale global convection characteristics of the high-latitude ionosphere to be reproduced. The model contains no discontinuities in the ion convection velocity and as such should be useful in F region chemical models. The number of variables in the model allow such features as the dayside throat and the Harang discontinuity to be modeled. The applicability of the model to magnetospheric physics is limited by the exclusion of large-magnitude small-scale flow features associated with discrete arcs and by the inability of the model to produce separate flow cells at the same local time.

Heelis, R. A.↗
NASA NTRS1982

Modeling of high-latitude currents in a substorm

The currents and electric fields in the area covered by the poleward set of field-aligned currents are computed by means of a quantitative model, in which the high-latitude band considered carries most of the poleward electrojet, and lies poleward of the region covering the inner magnetosphere and corresponding ionosphere. The Birkeland current and aurorally enhanced conductivity are assumed to be uniformly distributed across the band. The time-dependent conductivity model used is based on electron fluxes and mean energies measured from the S3-2 satellite. Joule heating of the upper atmosphere was found to be about 2 x 10 to the 11th W during the substorm period. Model values for the strength of the electrojet and the amount of Joule heating agree to within about 20% with results based on a simple Cowling conductivity band.

Karty, J. L.↗
NASA NTRS1981

Dependence of polar cap potential drop on interplanetary parameters

The convection potential drop across the polar cap is computed from data obtained on high-inclination low-altitude satellites. Potential measurements are correlated with various combinations of parameters measured simultaneously in the upstream solar wind. Most of the potential drop is successfully predicted by merging theory, although a significant background potential drop of 35 kV does not depend on IMF parameters and is attributed to a process other than merging. Results indicate that small values of the IMF are amplified by a factor of 5-10 at the dayside magnetopause, which, when taken into account, improves correlations between IMF parameters and polar cap potential drop. Potential drop is better correlated with IMF parameters than with geomagnetic indices, due to nonlinear response of the magnetosphere affecting geomagnetic activity indices.

Reiff, P. H.↗
NASA NTRS1981

Quantitative simulation of a magnetospheric substorm. I - Model logic and overview

Results of a comprehensive computer simulation of the behavior of the earth's inner magnetosphere during a substorm-type event are reported. It is pointed out that the computer model self-consistently computes electric fields, currents, and plasma distributions and velocities in the inner-magnetosphere/ionosphere system; parallel electric fields and ionospheric neutral winds, however, are not included. The basic equations of the model are derived, and the inputs are described. An overview of the results is also given. The first appendix contains derivations of general, useful laws of bounce-averaged gradient, curvature, and E x B drifts in a plasma with isotropic pitch angle distribution. The second appendix gives a description of the numerical method used in the simulation.

Harel, M.↗
NASA NTRS1981

Quantitative simulation of a magnetospheric substorm. II - Comparison with observations

Results of the computer simulation of the behavior of the inner magnetosphere during the substorm-type event of September 19, 1976, are discussed. The computed electric fields are found to compare satisfactorily with electric fields measured from S3-2, although there are detailed differences. The three general features on which the model and observations are in good agreement are (1) the magnitude and direction of the high-latitude electric field, (2) the degree to which the low-latitude ionosphere is shielded from the high-latitude convection electric field, and (3) the fact that the poleward electric field on the duskside is significantly larger, on the average, than the equatorward electric field on the dawnside. Simple formulas are presented that give rough estimates of global Joule heating rates from observable parameters.

Harel, M.↗
NASA NTRS1981

Quantitative simulation of a magnetospheric substorm. III - Plasmaspheric electric fields and evolution of the plasmapause

Results of a substorm simulation are used to investigate the penetration of substorm-associated electric fields into the plasmasphere. Near 4 earth radii in the equatorial plane, the time-dependent electric field model is characterized by eastward components in the dusk-midnight local time sector and westward components after midnight. With the exception of a small region just before dusk, the model predicts eastward electric field components throughout the daytime sector. The characteristic radial component is directed inward at all local times with the exception of a small region just after dawn. It is noted that these results compare favorably with available whistler and incoherent-scatter radar measurements obtained during magnetically disturbed periods. By assuming an initial plasmapause shape and by following the computed E x B drift trajectories of plasma flux tubes from that initial boundary, the short-term evolution of the plasmapause during the substorm-like event of September 19, 1976, is examined.

Spiro, R. W.↗
NASA NTRS1981

Cusp region particle precipitation and ion convection for northward interplanetary magnetic field

Data from Atmosphere Explorer D for periods of strong northward interplanetary magnetic field are discussed. In the dayside magnetospheric cusp region energy time spectrograms of suprathermal positive ion fluxes exhibit a characteristic 'V' pattern as the spacecraft moves toward higher latitudes; that is, with the peak in the energy spectrum falling in energy and then rising again. Convection velocities follow this pattern closely with strong eastwest flows (with antisunward components) occurring in the equatorward half of the 'V' and significant sunward flows occurring in the poleward half of the 'V'. These patterns can be understood qualitatively in terms of a model of ionospheric electric potential produced by the known dependence of Birkeland current densities on magnetic activity.

Burch, J. L.↗
NASA NTRS1980

Cusp proton signatures and the interplanetary magnetic field

The variation of proton average energy with latitude in the cusp has been suggested as an indicator of the means of particle entry. If magnetic merging is the principal means of particle entry, the proton average energy should fall with increasing latitude; if diffusion is the principal means, the average energy should first fall and then briefly rise as a function of latitude, showing a 'V' signature. In the present work, 60 selected cusp passes of the AE-D satellite for which IMP-J interplanetary or magnetosheath magnetic-field data were available were examined. About one-third of these passes showed clear or likely merging-type energy dispersions; a third showed clear or likely V-type energy dispersions, and a third showed unclear or no energy dispersions. The results are strongly correlated with the IMF - the merging signatures are associated with southward IMF and the V signatures with northward IMF. Unclear cases are associated with unsteady or weakly northward IMF.

Reiff, P. H.↗
NASA NTRS1980

Cusp region particle precipitation and ion convection for northward interplanetary magnetic field

Data from Atmosphere Explorer D for periods of strong northward interplanetary magnetic field show the following characteristic behavior in the dayside magnetospheric cusp region: energy-time spectrograms of suprathermal positive ion fluxes exhibit a characteristic 'V' pattern as the spacecraft moves toward higher latitudes; that is, with the peak in the energy spectrum falling in energy and then rising again. Convection velocities follow this pattern closely with strong east-west flows (with antisunward components) occurring in the equatorward half of the 'V' and significant sunward flows occurring in the poleward half of the 'V'. These patterns can be understood qualitatively in terms of a model of ionospheric electric potential produced by the known dependence of Birkeland current densities on magnetic activity.

Burch, J. L.↗
NASA NTRS1979

Rapid subauroral ion drifts observed by Atmosphere Explorer C

Results are presented for an investigation of rapid subauroral ion drift features using data obtained over a nearly five-year period from the ion RPA/drift meter on Atmosphere Explorer-C. These latitudinally narrow features are found to be confined predominantly to the local time sector between 18:00 and 02:00 hr. They occur either singly or as multiple events, one of which almost always straddles the equatorward edge of the auroral zone. Their occurrence probability suggests a dependence of magnetic substorm activity.

Spiro, R. W.↗
NASA NTRS1978

Ion convection and the formation of the mid-latitude F region ionization trough

Total ion concentration and ion drift velocity data from Atmospheric Explorer C are used to examine the convective flow of plasma in the vicinity of the midlatitude F region ionization trough. It is found that the low-latitude portion of the premidnight trough is a region of slow eastward plasma drift while the poleward portion is characterized by generally westward flow. The reversal from eastward to westward flow is described. It is proposed that the plasma flux tubes within the premidnight trough have corotated eastward into the evening local time sector from dusk before stagnating and flowing westward at higher latitudes in the nighttime sector. The role of F region recombination in trough formation is considered.

Spiro, R. W.↗