Engineering topics

Baker, D. N.

Publications and source records attributed to Baker, D. N..

At least 397 records · Page 22

NASA NTRS1992

ISEE 3 plasmoid and TCR observations during an extended interval of substorm activity

On April 9-11, 1983, the ISEE 3 spacecraft was continuously located within the earth's magnetotail for more than 36 hours at downstream distances of X = -76 to -80 R(e). During this span of time, 12 major intervals of substorm activity were observed in the AL index with good ISEE 3 telemetry coverage for 11 of them. In addition, there were two small substorms outside of these intervals, both with complete observations in the distant tail. This unusual ISEE 3 data set provides a unique opportunity to test the predictions of the near-earth neutral line model. In particular, the hypothesis that energy stored in the tail lobes during the growth phase is later dissipated, in part, through the release of one or more plasmoids following expansion phase onset is examined. Clear growth phase enhancements in the lobe magnetic field intensity preceded the onsets of nine of the substorms. Plasmoids, or their lobe signatures, traveling compression regions (TCRs), were observed at ISEE 3 in association with all 11 of the major substorm intervals for which there were ISEE observations, as well as for the two small substorms. No plasmoids or TCRs were observed in the absence of substorm activity. If these ISEE 3 observations are representative, then the release of plasmoids down the tail may be a feature common to all substorms.

Slavin, J. A.↗

NASA NTRS1992

Jovian electron transport to the polar heliosphere - An analogy to magnetospheric recirculation

The theory of magnetospheric recirculation for cyclic electron energization and transport may apply in part to heliospheric transport of Jovian electrons if enhanced cross-IMF propagation occurs at heliospheric altitudes near and below the solar wind transition region. Low altitude, ecliptic-to-polar transport would short-circuit conventional interplanetary diffusion, facilitate rapid access to the polar heliosphere with minimal adiabatic energy losses, and provide a seed population for acceleration to 100-1000 MeV energies at the solar wind termination shock and in the heliomagnetotail.

Cooper, J. F.↗

NASA NTRS1991

Modeling the growth phase of a substorm using the Tsyganenko model and multi-spacecraft observations - CDAW-9

The CDAW-9 Event C focused upon the early part of 3 May 1986 when a large substorm onset occurred at 0111 UT. By modifying the Tsyganenko 1989 magnetic field model, a model is constructed in which the near-earth current systems are enhanced with time to describe the observed development of the tail magnetic field during the growth phase. The cross-tail current intensity and the thickness of the current sheet are determined by comparison with three spacecraft in the near-earth tail. The location of the auroral bulge as recorded by the Viking imager is mapped to the equatorial current sheet. The degree of chaotization of the thermal electrons is estimated, and the consequences to the tail stability towards on tearing are discussed. It is concluded that the mapping of the brightening region in the auroral oval corresponds to the regions in the tail where the current sheet may be unstable towards ion tearing.

Pulkkinen, T. I.↗

NASA NTRS1991

Rocket measurements of relativistic electrons - New features in fluxes, spectra and pitch angle distributions

Novel features are presented of precipitating relativistic electron fluxes measured on a spinning sounding rocket payload at midday between altitudes of 70 and 130 km in the auroral region. The sounding rocket was launched during a relativistic electron enhancement event of modest intensity. Electron fluxes were measured for a total of about 210 seconds at energies from 0.1 to 3.8 MeV, while pitch angle was sampled from 0 to 90 deg every spin cycle. Electrons with energies below about 0.2 MeV showed isotropic pitch angle distributions during most of the first 90 sec of data, while at higher energies the electrons had the highest fluxes near the mirroring angle (90 deg); when they occurred, the noted downward bursts were seen at all energies. The low-altitude fluxes are compared with those measured at geostationary orbit, and it is found that the low-altitude fluxes are much higher than expected from a simple mapping of a pancake distribution at high altitudes.

Herrero, F. A.↗

NASA NTRS1991

Examination of time-variable input effects in a nonlinear analogue magnetosphere model

The plasma physical analog model (an extension of the damped, harmonic-oscillator dripping faucet model) is employed to consider explicitly the effect of time-varying the inputs. This work is equivalent to considering the effects of northward and southward turnings of the interplanetary magnetic field for various periods of time. It is found that relatively extended episodes (not less than 2 hours) of turned-on input with shorter (about 1 hour) periods of turned-off input lead to model behavior much like the continuously driven case. Going to short input intervals with longer periods of zero input leads to highly irregular and dramatically fluctuating episodes of magnetotail unloading. These results give an insight into the diversity of apparent magnetospheric responses during relatively isolated substorm conditions. This work shows the absolutely critical interdependence (in a nonlinear dynamical system) of input phasing and internal magnetospheric response cycles.

Baker, D. N.↗

NASA NTRS1991

Linear prediction filters for linear and nonlinear modeled geomagnetic activity

It is shown that the Faraday loop analog model of geomagnetic activity exhibits both the directly driven and loading-unloading magnetospheric responses to solar wind input. It is further shown that the directly driven component is a linear response to loading while the loading-unloading response is nonlinear. Linear prediction filters which relate model input to output are discussed. By either allowing or suppressing the loading-unloading model response filters that relate to nonlinear or linear dynamics, respectively, have been computed. Filters that described the directly driven response are finite ranged; they asymptote to zero with increasing lag on a time scale that is fixed by the dissipation rate of the model. Filters that describe the nonlinear total response are infinite ranged; they asymptote with increasing lag to large amplitude periodic oscillations. Some implications of these infinite ranged filters are discussed.

Klimas, A. J.↗

NASA NTRS1991

Relativistic electron enhancements - Simultaneous measurements from synchronous and low altitude satellites

This paper presents, for the first time, simultaneous measurements of trapped relativistic electron enhancements at synchronous altitude and precipitating electrons in the bounce loss cone at low altitudes. The measurements show that the daily variations in the precipitation flux for L greater than 5 correlated well with the daily variations in the total flux at high altitude, both with respect to sudden enhancements as well as flux depletions. The daily averaged precipitating flux (E greater than 1 MeV) at L = 6.1 to 7.1 was about 0.3 percent of the daily averaged directional flux (E not less than 1.5 MeV) observed at synchronous altitude, whereas within narrow spikes the precipitating directional fluxes were often within a factor of 10 of the daily averaged trapped fluxes. Strong depletions in the synchronous altitude not less than 1.5 MeV electron intensities are shown to be associated with low-altitude measurements of the equatorward movement of precipitating spikes to lower L shells.

Imhof, W. L.↗

NASA NTRS1991

Precipitating relativistic electrons - Their long-term effect on stratospheric odd nitrogen levels

Using electron count rate data at geostationary orbit, daily energy spectra, extending from 30 keV to 15 MeV, have been developed for trapped relativistic electrons at 6.6 earth radii. These spectra have been used to model the flux of these electrons into the atmosphere at 120 km. Energy deposition calculations permit daily sources of HO(x) and NO(y) to be calculated at auroral and subauroral latitudes due to relativistic electron precipitation (REP) for the period June 13, 1979, through June 4, 1988. Both short-term and long-term source variations are quite large over the period considered. The results suggest that a significant contribution to the anomalously large and unexplained global O3 declines between 1979 and 1985 has been made by the catalytic destruction of O3 by odd nitrogen in the lower stratosphere at mid to high latitudes. The results also provide evidence for a clear and strong linkage between solar variability, the state of the magnetosphere, and the chemical climatological state of the middle and lower atmosphere.

Callis, Linwood B.↗

NASA NTRS1991

Indications of low dimensionality in magnetospheric dynamics

Using three separate but related approaches, the question of whether the dynamic response of the magnetosphere to the solar wind input may be described by a low-order system of equations is examined. First, it is determined that the dimension of the subset (the attractor) in the high-dimensional magnetospheric phase space associated with the westward auroral electrojet (AL) index for some of the data sets compiled by Bargatze et al. (1985) is 4.0 + or - 0.2, seemingly independent of activity level. Second, direct modeling of the magnetosphere, considering the bulk properties of the tail plasma, leads to a system of equations that is similar to those previously reported as a dripping faucet model; here, the focus is specifically on the prediction of a natural frequency in this model. Finally, a peak is identified with the predicted frequency in power spectra of AL computed for intervals with both low and high activity. Peaks at other frequencies also appear in the spectra, and such resonances would be expected for a chaotic nonlinear oscillator. Combining these approaches it is concluded that at least some aspects of magnetospheric dynamics may be meaningfully modeled by low-dimensional sets of equations.

Roberts, D. A.↗

NASA NTRS1990

The substorm event of 28 January 1983 - A detailed global study

A comprehensive timeline of the growth, expansion, and recovery phases of a small isolated substorm with an expansion phase onset at 07:39 U.T. on January 28, 1983 is provided. The data sets examined include those from the electron-plasma, magnetometer, and energetic-particle instruments onboard ISEE-3. In addition to these data sets, a number of other spacecraft and ground-based data is utilized, including the magnetospheric energy-input rates evaluated in the upstream solar wind and imaging sequences used for examining auroral features during growth and expansion phases. Substorm energy-input and -output relationships are estimated quantitatively, and the timing and physical dimensions of the distant tail disturbance implied by global observations available are evaluated.

Baker, D. N.↗

NASA NTRS1990

Field-aligned current signatures in the near-tail region. II - Coupling between the region 1 and the region 2 systems

The development of the substorm-associated current signature in the near magnetotail region is investigated on the basis of ground magnetometer, satellite magnetic field, and energetic particle data collected during the March 28, 1979 substorm event. It is shown that the development of the region 1 and the region 2 systems during substorms should be viewed in terms of the formation of a new current system in the near-tail system, rather than merely an enhancement in the current intensity of preexisting systems. Experimental data suggest that the region 2 system is as important as the region 1 system and must be taken into account. The development of the region 2 system and the three-dimensional current closure are discussed.

Ohtani, S.↗

NASA NTRS1990

Linear prediction filter analysis of relativistic electron properties at 6.6 R(E)

The relationship between relativistic electron flux variations at 6.6 R(E) and various published indices and solar wind properties is studied. An attempt is made to characterize the temporal and dimensional relationships between solar wind or magnetic indices and electron flux enhancements. It is shown that the solar wind speed upstream of the earth's magnetosphere is correlated with large increases in the flux of highly relativistic electrons at geostationary orbit.

Baker, D. N.↗

NASA NTRS1990

The interaction of impulsive solar wind discontinuities with the magnetosphere - A multi-satellite case study

Data collected on September 4-5, 1984 by the outbound AMPTE/IRM spacecraft which stayed just outside the expanding earth's bow shock for 7.5h are examined. The data are gathered during an unusual period for which the solar wind pressure and magnetic field are relatively constant except for two discontinuities with associated approximately equal to 1 min duration pressure pulses. The observations indicate that the bow shock reacts rapidly to solar wind dynamic pressure variations; that both discontinuity/pressure pulse events were followed more or less immediately by a decrease in the geosynchronous particle fluxes, indicating the growth phase of a substorm and possibly also the shadowing of energetic ions by the compressed magnetopause followed after 10-30 min by a sudden enhancement in the energetic particles which began on the nightside and drifted to the dayside; and sudden impulse ground signatures are observed which seem to depend critically on the IMF orientation as well as on the longitude and latitude of the particular ground stations.

Labelle, J.↗

NASA NTRS1990

IMP-8 observations of traveling compression regions - New evidence for near-earth plasmoids and neutral lines

An examination of IMP-8 tail lobe magnetic field measurements has been conducted to determine whether the traveling compression region (TCR) phenomena detected by ISEE-3 in the distant geotail, and believed to be caused by tailward moving plasmoids, are present closer to the earth. The study produced 16 examples of TCRs at distances of X = -31 to -37 R(E). For two events considered in detail, TCRs were observed in close association with substorm growth phase signatures in the lobes. The lengths of these TCRs are estimated to be 8-12 R(E). The conclusion is that the IMP-8 TCR observations provide new evidence that small plasmoids and, hence, multiple reconnection neutral lines can sometimes exist earthward of X = -35 R(E).

Slavin, J. A.↗

NASA NTRS1990

A possible case of radially antisunward propagating substorm onset in the near-earth magnetotail

It is generally thought that the local effects associated with substorm onset in the near-earth magnetotail (R less than about 10 earth radii) have a component of propagation which is radially earthward. This study presents a case during which it is possible that the local effects of substorm onset propagated radially antisunward, examining energetic-ion and magnetic-field data from AMPTE/CCE and energetic-particle data from the GEO satellite 1982-019 during a period of weak substorm activity on June 11, 1985. Although the effects of this event on the ground were very weak, the substorm had a dramatic effect on at least one portion of the near-earth magnetotail. During the period the spacecraft were in an unusually close radial alignment. The data show that phenomena associated with the local effects of substorm onset began at or near GEO before they were observed at CCE. This event is best explained by a near-earth disruption of the cross-tail current sheet and the consequent formation of a substorm current wedge, with a component of expansion antisunward down the tail.

Lopez, R. E.↗

NASA NTRS1990

Extreme energetic particle decreases near geostationary orbit - A manifestation of current diversion within the inner plasma sheet

A qualitative model of magnetic field reconfiguration as might result from neutral line formation in the central plasma sheet late in a substorm growth phase is considered. It is suggested that magnetic reconnection probably begins before the substorm expansion phase and that cross-tail current is enhanced across the plasma sheet both earthward and tailward of a limited region near the neutral line. Such an enhanced cross-tail current earthward of the original X line region may contribute to thinning the plasma sheet substantially, and this would in turn affect the drift currents in that location, thus enhancing the current even closer toward the earth. In this way a redistribution and progressive diversion of normal cross-tail current throughout much of the inner portion of the plasma sheet could occur. The resulting intensified current, localized at the inner edge of the plasma sheet, would lead to a very thin plasma confinement region. This would explain the very taillike field and extreme particle dropouts often seen late in substorm growth phases.

Baker, D. N.↗

NASA NTRS1990

The evolution from weak to strong geomagnetic activity - An interpretation in terms of deterministic chaos

An analogue of the magnetosphere developed on the basis of Shaw's (1984) dripping faucet model was used to model the mechanisms of the magnetospheric response to energy transfer from the solar wind. It is demonstrated that geomagnetic activity results from nonlinearly coupled physical processes and that the strength and the nature of the coupling changes dramatically as the magnetosphere is driven harder and harder by increasing energy input. Based on initial results obtained from the model, is is suggested that a chaotic transition takes place in the analogue system as the loading rate is increased beyond a critical value. This model is able to explain many of the features in the results of linear prediction filtering techniques.

Baker, D. N.↗

NASA NTRS1990

Extreme energetic particle decreases near geostationary orbit - A manifestation of current diversion within the inner plasma sheet

A qualitative model of cross-tail current flow is considered. It is suggested that when magnetic reconnection begins, the current effectively flows across the plasma sheet both earthward and tailward of the disruption region near the neutral line. It is shown that an enhanced cross-tail current earthward of this region would thin the plasma sheet substantially due to the magnetic pinch effect. The results explain the very taillike field and extreme particle dropouts often seen late in substorm growth phases.

Baker, D. N.↗