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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Protons as the prime contributors to storm time ring current

Following a large sudden commencement on June 17, 1972, a large magnetic storm evolved, with a well-developed main phase and recovery phase. Explorer 45 (S3-A), with its apogee near 16 hours local time in June, measured the equatorial particle populations and magnetic field throughout this period. By use of data obtained during the symmetric recovery phase it is shown that through a series of self-consistent calculations, the measured protons, with energies from 1 to 872 keV, can account for almost all of the observed ring current magnetic effects within the limits of experimental uncertainties. This enables us to set an upper limit to the heavy ion contribution to the storm time ring current of a few percent of the proton contribution.

Berko, F. W.↗
NASA NTRS2023

The Faraday Effect Tracker of Coronal and Heliospheric Structure (FETCH) Instrument

There continue to be open questions regarding the solar wind and coronal mass ejections (CMEs). For example: how do magnetic fields within CMEs and corotating/stream interaction regions (CIRs/SIRs) evolve in the inner heliosphere? What is the radially distributed magnetic profile of shock-driving CMEs? What is the internal magnetic structure of CMEs that cause magnetic storms? It is clear that these questions involve the magnetic configurations of solar wind and transient interplanetary plasma structures, for which we have limited knowledge. In order to better understand the origin of the magnetic field variability in steady-state structures and transient events, it is necessary to probe the magnetic field in Earth-directed structures/disturbances. This is the goal of the Multiview Observatory for Solar Terrestrial Science (MOST) mission (Gopalswamy et al., 2022). For MOST to answer the aforementioned questions, we propose the instrument concept of the Faraday Effect Tracker of Coronal and Heliospheric structures (FETCH), a simultaneous quad-line-of-sight polarization radio remote-sensing instrument. With FETCH, spacecraft radio beams passing through the Sun–Earth line offer the possibility of obtaining information of plasma conditions via analysis of radio propagation effects such as Faraday rotation and wave dispersion, which provide information of the magnetic field and total electron content (TEC). This is the goal of the FETCH instrument, one of ten instruments proposed to be hosted on the MOST mission. The MOST mission will provide an unprecedented opportunity to achieve NASA’s heliophysics science goal to “explore and characterize the physical processes in the space environment from the Sun” (Gopalswamy et al., 2022).

Solar corona↗
NASA NTRS1982

A comparison of the 0.1-17 keV/e ion composition in the near equatorial magnetosphere between quiet and disturbed conditions

Data from the near-equatorial magnetosphere are analyzed by comparing the plasma composition during storm conditions with the composition during extended periods of low magnetic activity. It is found that at L less than or equal to 5, the O(+) is typically comparable to the H(+) in density and is often the dominant species, particularly during quiet times and at the inner edge of the region of significant fluxes. The He(+) in most cases contributes a significant fraction of the density and is sometimes the second most abundant species, following the O(+). Another finding is that both the He(+)/H(+) and the O(+)/H(+) ratios peak at the lowest L values and are, on the average, higher during quiet times than they are during the early main phase of major magnetic storms; this is seen as suggesting that charge exchange may be a significant loss process at low L. It is pointed out that the mean energies of the H(+), He(+), and O(+) ions often decrease gradually with decreasing L toward the inner edge of the energetic particle population.

Lennartsson, W.↗
NASA NTRS1985

Dynamics of the earth's ring current - Theory and observation

The development of currents within an arbitrary distribution of particles trapped in the geomagnetic field is described. These currents combine to form the earth's ring current and thus are responsible for the worldwide depressions of surface magnetic field strength during periods of magnetic activity known as magnetic storms. Following a brief review of trapped particle motion in magnetic fields, ring current development is described and presented in terms of basic field and particle distribution parameters. Experimental observations then are presented and discussed within the theoretical framework developed earlier. New results are presented which, in the area of composition and charge state observations, hold high promise in solving many long standing ring current problems. Finally, available experimental results will be used to assess the present understanding as to ring current sources, generation, and dissipation.

Williams, D. J.↗
NASA NTRS1994

Accurate modeling of F-region electron densities

In the past year, we have made considerable progress in a number of areas including algorithm development, completion of two major case studies, and the development of a new EUV flux model. As a result, there has been a major improvement in our ability to model global emissions in support of NASA's imaging plans. Activity highlights include the following: developed a new algorithm to allow physical models to reproduce observed NmF2; investigated the relationship between NmF2 and F10.7 at Millstone Hill during 1990; developed a new solar EUV flux model; statistical survey of anomalously high nighttime electron T(sub e) at Millstone Hill; conducted a case study of the March 1990 magnetic storm; and conducted a comparison between theory and data of magnetically quiet behavior of the winter ionosphere at Millstone Hill.

Source record↗
NASA NTRS2012

The Magnetic and Shielding Effects of Ring Current on Radiation Belt Dynamics

The ring current plays many key roles in controlling magnetospheric dynamics. A well-known example is the magnetic depression produced by the ring current, which alters the drift paths of radiation belt electrons and may cause significant electron flux dropout. Little attention is paid to the ring current shielding effect on radiation belt dynamics. A recent simulation study that combines the Comprehensive Ring Current Model (CRCM) with the Radiation Belt Environment (RBE) model has revealed that the ring current-associated shielding field directly and/or indirectly weakens the relativistic electron flux increase during magnetic storms. In this talk, we will discuss how ring current magnetic field and electric shielding moderate the radiation belt enhancement.

Fok, Mei-Ching↗
NASA NTRS1981

Observations of energetic helium ions in the earth's radiation belts during a sequence of geomagnetic storms

Observations of energetic (MeV) helium ions made with Explorer 45 during a sequence of magnetic storms during June through December of 1972 are presented. It is noted that the first of these storms started on June 17 and had a Dst index excursion to -190 gamma and that the MeV helium ions were perturbed primarily beyond 3 earth radii in the equatorial radiation belts with a typical flux increase of an order of magnitude at L equal to 4. The second storm period was in August and was associated with very major solar flare activity. While the Dst extremum was at best 35 gamma less than the June storm, this period can be characterized as irregular (or multi-storm) with strong compression of the magnetosphere and very large (order of magnitude) MeV helium ion flux enhancements down to L approximately equal to 2. After this injection, the trapped helium ion fluxes showed positive spherical slope with the peak beyond 3.15 MeV at L equal to 2.5; at the lowest observable L shells, little flux decay was seen during the remainder of the year.

Spjeldvik, W. N.↗
NASA NTRS2016

Ionospheric Storm Effects and Equatorial Plasma Irregularities During the 17-18 March 2015 Event

The intense magnetic storm on 17-18 March 2015 caused large disturbances of the ionosphere. Based on the plasma density (Ni) observations performed by the Swarm fleet of satellites, the Gravity Recovery and Climate Experiment mission, and the Communications/Navigation Outage Forecasting System satellite, we characterize the storm-related perturbations at low latitudes. All these satellites sampled the ionosphere in morning and evening time sectors where large modifications occurred. Modifications of plasma density are closely related to changes of the solar wind merging electric field (E (sub m)). We consider two mechanisms, prompt penetration electric field (PPEF) and disturbance dynamo electric field (DDEF), as the main cause for the Ni redistribution, but effects of meridional wind are also taken into account. At the start of the storm main phase, the PPEF is enhancing plasma density on the dayside and reducing it on the nightside. Later, DDEF takes over and causes the opposite reaction. Unexpectedly, there appears during the recovery phase a strong density enhancement in the morning/pre-noon sector and a severe Ni reduction in the afternoon/evening sector, and we suggest a combined effect of vertical plasma drift, and meridional wind is responsible for these ionospheric storm effects. Different from earlier studies about this storm, we also investigate the influence of storm dynamics on the initiation of equatorial plasma irregularities (EPIs). Shortly after the start of the storm main phase, EPIs appear in the post-sunset sector. As a response to a short-lived decline of E (sub m), EPI activity appears in the early morning sector. Following the second start of the main phase, EPIs are generated for a few hours in the late evening sector. However, for the rest of the storm main phase, no more EPIs are initiated for more than 12 hours. Only after the onset of recovery phase does EPI activity start again in the post-midnight sector, lasting more than 7 hours.This comprehensive view of ionospheric storm effects and plasma irregularities adds to our understanding of conditions that lead to ionospheric instabilities.

Zhou, Yun-Liang↗
NASA NTRS2010

Simulation and 'TWINS Observations of the 22 July 2009 Storm

TWINS is the first mission to perform stereo imaging of the Earth's ring current. The magnetic storm on 22 July 2009 is the largest storm observed since TWINS began routine stereo imaging in June 2008. On 22 July 2009, the Dst dropped to nearly -80nT at 7:00 and 10:00 UT. During the main phase and at the peak of the storm, TWINS 1 and 2 were near apogee and moving from pre-dawn to post-dawn local time. The energetic neutral atom (ENA) imagers on the 2 spacecraft captured the storm intensification and the formation of the partial ring current. The peak of the ENA emissions was seen in the midnight-to-dawn local-time sector. The development of this storm has been simulated using the Comprehensive Ring Current Model (CRCM) to understand and interpret the observed signatures. We perform CRCM runs with constant and time-varying magnetic field. The model calculations are validated by comparing the simulated ENA and ion flux intensities with TWINS ENA images and in-situ ion data from THEMIS satellites. Simulation with static magnetic field produces a strong shielding electric field that skews the ion drift trajectories toward dawn. The model's corresponding peak ENA emissions are always eastward than those in the observed TWINS images. On the other hand, simulation with a dynamic magnetic field gives better spatial agreements with both ENA and insitu particle data, suggesting that temporal variations of the geomagnetic field exert a significant influence upon global ring current ion dynamics.

Fok, Mei-Ching↗
NASA NTRS2011

Simulation and Twins Observations of the 22 July 2009 Storm

TWINS is the first mission to perform stereo imaging of the Earth's ring current. The magnetic storm on 22 July 2009 was at the time the largest storm observed since TWINS began routine stereo imaging in June 2008. On 22 July 2009, the Dst dropped to nearly .80 nT at 0700 and 1000 UT. During the main phase, and at the peak of the storm, TWINS 1 and 2 were near apogee and moving between predawn and postdawn local time. The energetic neutral atom (ENA) imagers on the two spacecraft captured the storm intensification and the formation of the partial ring current. The peak of the high-altitude ENA emissions was seen in the midnight-to-dawn local time sector. The development of this storm has been simulated using the comprehensive ring current model (CRCM) to understand and interpret the observed signatures. We perform CRCM runs with constant and time-varying magnetic field. The model calculations are validated by comparing the simulated ENA and ion flux intensities with TWINS ENA images and in situ ion data from a THEMIS satellite. Simulation with a static magnetic field produces a strong shielding electric field that skews the ion drift trajectories toward dawn. The model's corresponding peak ENA emissions are always more eastward than those in the observed TWINS images. On the other hand, the simulation with a dynamic magnetic field gives better spatial agreement with both ENA and in situ particle data, suggesting that temporal variations of the geomagnetic field exert a significant influence upon global ring current ion dynamics.

Fok, M.-C.↗
NASA NTRS1972

Synthesis of Jicamarca data during the great storm of March 8, 1970.

Continuous measurement of electron temperature and electron concentration during the great magnetic storm of Mar. 8, 1970, when the F2 peak rose as high as 800 km. Continuous measurements of the vertical component of E x B drift were made from 1130 to 1730 LT. A synthesis of the observed electron concentrations was made using a model that solved the time-dependent electron-ion continuity equation for O(+) and the molecular ions; the latter chemistry was included to improve the solutions at lower heights. It was found, using the observed values of vertical drift, that most of the observed features of the F2-region ionosphere were synthesized by the model. An interpretation of the synthesis that emphasizes the importance of horizontal diffusion at the equator is given. Observations are presented for Mar. 7, 8, and 9, 1970, including the Huancayo magnetograms, which display a close correlation with the drift measurements.

Woodman, R. F.↗
NASA NTRS1988

Ring current development during the great geomagnetic storm of February 1986

The variations of the ring current energy density and composition during the great magnetic storm of February 1986 were investigated using particle measurements obtained by the charge-energy-mass instrument on the AMPTE Charge Composition Explorer spacecraft. The ring current composition of this storm, which had a complicated main phase and a minimum Dst of -312 nT on February 9, was followed for five days from the prestorm quiet time to the early recovery phase. Results suggested that the very rapid initial Dst recovery (tau of about 9.3 hrs) in this storm resulted largely from the rapid loss of 75- to 100-keV O(+) via charge exchange in the inner portion of the ring current. It is proposed that a major O(+) + N(+) ring current component generally exists near the maximum phase of great storms.

Hamilton, D. C.↗
NASA NTRS1975

Analysis of satellite data on energetic particles of ionospheric origin

The morphology was studied of precipitating O(+) and H(+) ions in the energy range 0.7 equal to or less than E equal to or less than 12 keV during the storm-time period from December 16-18, 1971, which encompassed two principal magnetic storms. The results are described with emphasis on the temporal variations of parameters characterizing the intensity, average energy, and spatial location of the zones of precipitation of the two ionic species. One of the principal results was the finding that the intensity of the precipitating O(+) ions was well correlated with the geomagnetic indices which measure the strength of magnetospheric substorm activity and the strength of the storm-time ring current. Since the O(+) ions are almost certainly of ionospheric origin the correlations indicate that a previously unknown strong coupling mechanism existed between the magnetosphere and the ionosphere during the storm period.

Sharp, R. D.↗
NASA NTRS1990

Simplified model for solar cosmic ray exposure in manned Earth orbital flights

A simple calculational model is derived for use in estimating solar cosmic ray exposure to critical body organs in low-Earth orbit at the center of a large spherical shield of fixed thickness. The effects of the Earth's geomagnetic field, including storm conditions and the astronauts' self-shielding, are evaluated explicitly. The magnetic storm model is keyed to the planetary index K(sub p).

Wilson, John W.↗
NASA NTRS1987

Solar activity, magnetic clouds, and geomagnetic storms

Associational aspects of magnetic clouds and solar activity, and of magnetic clouds and geomagentic storms are described. For example, recent research has shown associations to exist between the launch of magnetic clouds directed Earthward from the Sun and, in particular, two forms of solar activity: flare-related, type II metric radio bursts and disappearing filaments (prominences). Furthermore, recent research has shown an association to exist between the onset of magnetic clouds on Earth and the initiation of geomagnetic storms. Based on these findings, STIP Intervals XV-XIX are examined for possible occurrences of Earthward-directed magnetic clouds.

Wilson, Robert M.↗
NASA NTRS1981

The electrical conductivity of the Earth's upper mantle as estimated from satellite measured magnetic field variations

Low latitude magnetic field variations (magnetic storms) caused by large fluctuations in the equatorial ring current were derived from magnetic field magnitude data obtained by OGO 2, 4, and 6 satellites over an almost 5 year period. Analysis procedures consisted of (1) separating the disturbance field into internal and external parts relative to the surface of the Earth; (2) estimating the response function which related to the internally generated magnetic field variations to the external variations due to the ring current; and (3) interpreting the estimated response function using theoretical response functions for known conductivity profiles. Special consideration is given to possible ocean effects. A temperature profile is proposed using conductivity temperature data for single crystal olivine. The resulting temperature profile is reasonable for depths below 150-200 km, but is too high for shallower depths. Apparently, conductivity is not controlled solely by olivine at shallow depths.

Didwall, E. M.↗