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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 109 records · Page 6
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NASA NTRS1981

Particle and Joule heating of the neutral polar thermosphere in cusp region using atmosphere Explorer-C satellite measurements

It is pointed out that thermospheric heating in the auroral zone and polar cap is of great importance to the variations in the high-latitude neutral wind and the resulting global temperature and densities. The considered investigation is concerned with relating in a quantitative manner the energy inputs from the Joule heating and particle inputs with the thermospheric responses, taking into account the cusp region, and the region of the eastward auroral electrojet. The data used in the investigation were obtained by the Atmosphere Explorer C satellite in late December 1974. Attention is given to electric fields derived from ion drift measurements, electric field strength and particle energy flux measured by the low energy electron experiment for AE-C orbit 4708, electron density contours, Joule heating contours, and height integrated Joule heating and particle energy flux.

Griffis, M.↗
NASA NTRS1982

Relationships between the Birkeland currents, ionospheric currents, and electric fields

Currents and electric fields in the ionosphere are calculated using a global model of the electron density including conjugate coupling along field lines. Incoherent scatter and rocket measurements of high-latitude electron densities are used to derive realistic variations of the polar conductivities as a function of magnetic activity. The Birkeland currents are specified in terms of three indices, and the relationship between these parameters and the auroral electrojets indices is examined along with the polar cap potential and the electric field at lower latitudes. A mathematical model of the currents, electric fields, and energy inputs produced by field aligned currents is developed, which is consistent with and specifiable in terms of measured geophysical indices.

Bleuler, E.↗
NASA NTRS1983

Solar wind control of the low-latitude asymmetric magnetic disturbance field

The extent to which the low latitude dawn-dusk magnetic asymmetry is controlled by the dawn-dusk solar wind motional electric field VBs and/or substorm processes measured by the westward auroral electrojet index AL is studied using the technique of empirical linear prediction filters. A new index, (ASYM), defined as the difference between dawn and dusk deviations in the X (geomagnetic Northward) magnetic field component, is used to measure the dawn-dusk asymmetry. Quantitative information which characterizes the coupling processes are provided by the empirically determined filters obtained from this analysis. Results indicate that some currents are directly driven by the solar wind-magnetosphere interaction and that their magnetic perturbations contribute to both the AL and ASYM indices. However, a portion of the AL index that is uncorrelated with VBs is correlated with ASYM which suggests that internal magnetospheric processes also contribute to AL and ASYM.

Clauer, C. R.↗
NASA NTRS1983

A case study of the response of the magnetosphere to changes in the interplanetary medium

A detailed analysis of world-wide ground based magnetometer data is presented, together with information on the plasma and magnetic field properties of the interplanetary medium and magnetosheath obtained from the ISEE 1 and 2 and IMP 8 spacecraft. The event concerned exhibited an interval of relatively stable southward IMF followed by a sharp northward turning. It is pointed out that during the interval of southward IMF there were occasional transient northward turnings with significant substorm expansive phase activity appearing to be triggered by these transient northward turnings. The final northward turning of the IMF was linked with an episode of strong magnetospheric substorm expansive phase activity after which the level of high latitude magnetic activity declined to a low level. Evidence is presented indicating that the driven system auroral electrojets begin to decay at the time of the northward turning of the IMF, even as the substorm expansive phase activity is initiated in the midnight sector. The collapse of the substorm current wedge during the final decay of high latitude activity is described in some detail, and it is shown that this collapse occurs progressively from east to west in a series of impulsive episodes.

Rostoker, G.↗
NASA NTRS1984

Ion cyclotron waves as a possible source of resonant auroral radar echoes

Some auroral radar Doppler data which show the presence of spectra not previously discussed are described. The data were obtained during highly distributed magnetic conditions with a relatively small 50 MHz radar pointed northeast of Ithaca, New York. The data are characterized by strong discrete echoes and display spectral peaks which are even narrower than type 1 and are centered at a considerably smaller Doppler shift. These echoes were present simultaneously with and adjacent in range to the commonly observed auroral spectra, and were probably obtained from a height of about 140 km or higher, well above the center of the auroral electrojet. The results are compared with existing electrojet instability theories, and other plasma instabilities which might be important are discussed. The Doppler shift suggests that the narrow spectra might be caused by ion cyclotron waves generated by field-aligned currents, but the observations cannot be fully explained by any of the theories.

Fejer, B. G.↗
NASA NTRS1985

Active experiments from ground

Recent ground-based stimulation and observations of ionospheric and magnetospheric phenomena are reported. The studies included amplification and emission generation by coherent ducted whistler mode signals in the magnetosphere, recipitation of radiation belt particles by the injection of VLF waves from ground-based sources, spectral broadening of the VLF signals during ionospheric propagation and the generation of ELF/VLF signals by HF heating of the auroral electrojet. The capabilities of controlled stimulation of the local terrestrial magnetic field environment provides the means for further investigations into the processes of energy exchange between waves and radiation belt particles and the interrelationships of the exchange with the energy coupling between the magnetosphere and ionosphere.

Inan, U. S.↗
NASA NTRS1986

Observations of field-aligned currents, waves, and electric fields at substorm onset

Substorm onsets, identified Pi 2 pulsations observed on the Air Force Geophysics Laboratory Magnetometer Network, are studied using magnetometer and electric field data from ISEE 1 as well as magnetometer data from the geosynchronous satellites GOES 2 and 3. The mid-latitude magnetometer data provides the means of both timing and locating the substorm onset so that the spacecraft locations with respect to the substorm current systems are known. During two intervals, each containing several onsets or intensifications, ISEE 1 observed field-aligned current signatures beginning simultaneously with the mid-latitude Pi 2 pulsation. Close to the earth broadband bursts of wave noise were observed in the electric field data whenever field-aligned currents were detected. One onset occurred when ISEE 1 and GOES 2 were on the same field line but in opposite hemispheres. During this onset ISEE 1 and GOES 2 saw magnetic signatures which appear to be due to conjugate field-aligned currents flowing out of the western end of the westward auroral electrojets. The ISEE 1 signature is of a line current moving westward past the spacecraft. During the other interval, ISEE 1 was in the near-tail region near the midnight meridian. Plasma data confirms that the plasma sheet thinned and subsequently expanded at onset. Electric field data shows that the plasma moved in the opposite direction to the plasma sheet boundary as the boundary expanded which implies that there must have been an abundant source of hot plasma present. The plasma motion was towards the center of the plasma sheet and earthwards and consisted of a series of pulses rather than a steady flow.

Smits, D. P.↗
NASA NTRS1988

Global Geospace Science Programme

The Global Geospace Science (GGS) Program, an element of the international Solar Terrestrial Physics Program dedicated to the study of the global plasma dynamics of the solar-terrestrial environment, is discussed. Past research on the injection of solar wind ions into the magnetosphere and on the detection of ions in the terrestrial ring current of both solar wind and ionospheric origins is reviewed, showing its relevance for the GGS program. Research on the interplanetary magnetic field, the auroral electrojet, the outer magnetosphere, the geomagnetic tail, the ionospheric electric field and the related electron precipitation is also addressed. The results demonstrate that the solar wind and the ionsophere both contribute to the magnetospheric particle population. Unanswered questions regarding hot plasma sources, transport processes, energy storage in the magnetic field, and energization of plasmas are discussed. The relevant mission strategy, instrumentation, theory and modeling, and data collection are addressed.

Parks, George↗
NASA NTRS1987

Plasma and magnetic field variations in the distant magnetotail associated with near-earth substorm effects

Examination of many individual event periods in the ISEE 3 deep-tail data set has suggested that magnetospheric substorms produce a characteristic pattern of effects in the distant magnetotail. During the growth, or tail-energy-storage phase of substorms, the magnetotail appears to grow diametrically in size, often by many earth radii. Subsequently, after the substorm expansive phase onset at earth, the distant tail undergoes a sequence of plasma, field, and energetic-particle variations as large-scale plasmoids move rapidly down the tail following their disconnection from the near-earth plasma sheet. ISEE 3 data are appropriate for the study of these effects since the spacecraft remained fixed within the nominal tail location for long periods. Using newly available auroral electrojet indices (AE and AL) and Geo particle data to time substorm onsets at earth, superposed epoch analyses of ISEE 3 and near-earth data prior to, and following, substorm expansive phase onsets have been performed. These analyses quantify and extend substantially the understanding of the deep-tail pattern of response to global substorm-induced dynamical effects.

Baker, D. N.↗
NASA NTRS1990

Low-dimensional chaos in magnetospheric activity from AE time series

The magnetospheric response to the solar-wind input, as represented by the time-series measurements of the auroral electrojet (AE) index, has been examined using phase-space reconstruction techniques. The system was found to behave as a low-dimensional chaotic system with a fractal dimension of 3.6 and has Kolmogorov entropy less than 0.2/min. These indicate that the dynamics of the system can be adequately described by four independent variables, and that the corresponding intrinsic time scale is of the order of 5 min. The relevance of the results to magnetospheric modeling is discussed.

Vassiliadis, D. V.↗
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 NTRS1992

The E-region Rocket/Radar Instability Study (ERRRIS) - Scientific objectives and campaign overview

The plasma instabilities in the low-attitude auroral ionosphere and the sources of free energy that drive these waves have been examined in detail in the framework of the ERRRIS project. Independent sets of experiments were carried out on board three NASA sounding rockets which were flown in conjunction with radar backscatter measurements from Esrange, Sweden, in 1988 and 1989. The backscatter measurements were taken by the 50 MHz CUPRI system for determining the launch conditions. The Eiscat incoherent scatter radar was used to take plasma drift, density, and temperature measurements on board two of the flown rockets. STARE observations of 1 m backscatter echoes were also made. The STARE velocity fields were in agreement with the Eiscat and in situ measured electric fields. Both CUPRI and STARE observed a very dynamic and changing auroral ionosphere over Esrange. It is concluded that the ERRRIS experiments provided valuable data on plasma instabilities in the auroral electrojet, including detailed in situ measurements of the two-stream wave spectrum and phase velocities.

Pfaff, R. F.↗
NASA NTRS1993

CDAW 9 analysis of magnetospheric events on May 3, 1986 - Event C

An intense geomagnetic substorm event on May 3, 1986, occurring toward the end of a strong storm period, is studied. The auroral electrojet indices and global imaging data from both the Northern and Southern Hemispheres clearly revealed the growth phase and expansion phase development for a substorm with an onset at 0111 UT. An ideally located constellation of four spacecraft allowed detailed observation of the substorm growth phase in the near-tail region. A realistic time-evolving magnetic field model provided a global representation of the field configuration throughout the growth and early expansion phase of the substorm. Evidence of a narrowly localized substorm onset region in the near-earth tail is found. This region spread rapidly eastward and poleward after the 0111 UT onset. The results are consistent with a model of late growth phase formation of a magnetic neutral line. This reconnection region caused plasma sheet current diversion before the substorm onset and eventually led to cross-tail current disruption at the time of the substorm onset.

Baker, D. N.↗
NASA NTRS1993

Reconstruction of low-dimensional magnetospheric dynamics by singular spectrum analysis

Singular spectrum analysis was used to study global magnetospheric dynamics using time series auroral electrojet (AE) data. The calculated correlation dimension of approximately 2.5 confirms the low dimensionality of earlier results. This technique indicated that global magnetospheric dynamics can be described by three variables whose dynamical features were obtained from the AE data.

Sharma, A. S.↗
NASA NTRS1993

Prediction of geomagnetic activity

A simple analytic model for the directly driven, adiabatic solar wind-magnetosphere-ionosphere coupling is derived on the basis of frontside reconnection and force balance in the tail. Magnetosphere-ionosphere coupling occurs through Alfven waves which are driven by changes of electric fields in the magnetosphere. The model provides an algorithm which calculates the directly driven part of the auroral electrojets from an observed solar wind variation. For two days in May 1979 the cross correlation between the prediction and observation of AE is greater than 0.9. This suggests that most of the geomagnetic activity during these two days was directly driven by the solar wind.

Goertz, C. K.↗
NASA NTRS1993

Factors influencing the intensity of magnetospheric substorms

A definition of the substorm is presented, and it is shown that the typical isolated substorm is produced by the superposition of effects of processes directly driven by the solar wind through dayside reconnection and those driven by unloading through nighttime reconnection. The single factor that determines whether a substorm will occur or not is the clock angle of the interplanetary magnetic field (IMF) around the earth-sun line. Only when this field points south of the GSM equatorial plane do the auroral electrojet indices depart from their quiet values. For a given clock angle, the level of activity increases with the IMF strength and solar wind velocity.

Mcpherron, R. L.↗
NASA NTRS1995

A description of the solar wind-magnetosphere coupling based on nonlinear filters

A nonlinear filtering method is introduced for the study of the solar wind -- magnetosphere coupling and related to earlier linear techniques. The filters are derived from the magnetospheric state, a representation of the magnetospheric conditions in terms of a few global variables, here the auroral electrojet indices. The filters also couple to the input, a representation of the solar wind variables, here the rectified electric field. Filter-based iterative prediction of the indices has been obtained for up to 20 hours. The prediction is stable with respect to perturbations in the initial magnetospheric state; these decrease exponentially at the rate of 30/min. The performance of the method is examined for a wide range of parameters and is superior to that of other linear and nonlinear techniques. In the magnetospheric state representation the coupling is modeled as a small number of nonlinear equations under a time-dependent input.

Vassiliadis, D.↗
NASA NTRS1996

Nonlinear dynamics of the magnetosphere and space weather

The solar wind-magnetosphere system exhibits coherence on the global scale and such behavior can arise from nonlinearity on the dynamics. The observational time series data were used together with phase space reconstruction techniques to analyze the magnetospheric dynamics. Analysis of the solar wind, auroral electrojet and Dst indices showed low dimensionality of the dynamics and accurate prediction can be made with an input/output model. The predictability of the magnetosphere in spite of the apparent complexity arises from its dynamical synchronism with the solar wind. The electrodynamic coupling between different regions of the magnetosphere yields its coherent, low dimensional behavior. The data from multiple satellites and ground stations can be used to develop a spatio-temporal model that identifies the coupling between different regions. These nonlinear dynamical models provide space weather forecasting capabilities.

Sharma, A. Surjalal↗