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At least 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Comparison of Magnetospheric Multiscale Ion Jet Signatures with Predicted Reconnection Site Locations at the Magnetopause

Magnetic reconnection at the Earths magnetopause is the primary process by which solar wind plasma and energy gains access to the magnetosphere. One indication that magnetic reconnection is occurring is the observation of accelerated plasma as a jet tangential to the magnetopause. The direction of ion jets along the magnetopause surface as observed by the Fast Plasma Instrument (FPI) and the Hot Plasma Composition Analyzer (HPCA) instrument on board the recently launched Magnetospheric Multiscale (MMS) set of spacecraft is examined. For those cases where ion jets are clearly discerned, the direction of origin compares well statistically with the predicted location of magnetic reconnection using convected solar wind observations in conjunction with the Maximum Magnetic Shear model.

Petrinec, S. M.↗
DOE OSTI2015

A DETERMINATION OF THE NORTH–SOUTH HELIOSPHERIC MAGNETIC FIELD COMPONENT FROM INNER CORONA CLOSED-LOOP PROPAGATION

A component of the magnetic field measured in situ near the Earth in the solar wind is present from north–south fields from the low solar corona. Using the Current-sheet Source Surface model, these fields can be extrapolated upward from near the solar surface to 1 AU. Global velocities inferred from a combination of interplanetary scintillation observations matched to in situ velocities and densities provide the extrapolation to 1 AU assuming mass and mass flux conservation. The north–south field component is compared with the same ACE in situ magnetic field component—the Normal (Radial Tangential Normal) Bn coordinate—for three years throughout the solar minimum of the current solar cycle. We find a significant positive correlation throughout this period between this method of determining the Bn field compared with in situ measurements. Given this result from a study during the latest solar minimum, this indicates that a small fraction of the low-coronal Bn component flux regularly escapes from closed field regions. The prospects for Space Weather, where the knowledge of a Bz field at Earth is important for its geomagnetic field effects, is also now enhanced. This is because the Bn field provides the major portion of the Geocentric Solar Magnetospheric Bz field coordinate that couples most closely to the Earth’s geomagnetic field.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

Energetic ions upstream of planetary bow shocks: Fermi acceleration or leakage

Spacecraft observations of Jupiter, Saturn, and Earth planetary bow shocks are assessed. For Jupiter, the unique composition of magnetospheric plasma, where oxygen and sulfur ions are major components, and the simultaneous presence of MeV electrons enable identification of the upstream particles as originating from within the magnetosphere. The observations at Saturn are phenomonologically similar, but no unique tracer element exists which can identify the origin. Earth observations show that substantial energetic particle activity occurs within the Earth's plasma sheet when upstream ions and electrons are observed in the interplanetary medium. Observations of the three planets are discussed to compare in-situ acceleration in the foreshock region vs. leakage of already accelerated ions from the parent magnetosphere. It is concluded that the evidence favors magnetospheric leakage.

Krimigis, S. M.↗
DOE OSTI2017

SHIELDS Predicting Hazards that Results from Solar Storms

Extreme weather happens worldwide and it takes place in the magnetosphere. The magnetosphere is the place where the majority of earth’s satellites reside. These satellites provide weather forecasting and serve as national defense. When solar storms take place, they can damage satellites.

58 GEOSCIENCES↗
NASA NTRS1976

Substorm observations of magnetic perturbations and ULF waves at synchronous orbit by ATS-1 and ATS-6

In the empirical study of the geomagnetic cavity, the synchronous equatorial orbit has been shown to be a most advantageous site for scientific measurements. Satellites in this orbit are fixed in the earth's main magnetic field so that the records are not dominated by changes due to satellite motion through this field. Also, the satellites traverse the same geometric region of space daily, thus facilitating statistical studies of magnetospheric phenomena. Thirdly, the magnetic field lines leaving the earth's surface near the auroral zone cross the equatorial plane close to this orbit, thus subjecting the region to a number of such phenomena. Previous observations at synchronous orbit with the UCLA fluxgate magnetometers on ATS-1 and ATS-6 have revealed a variety of substorm-associated field variations. These effects may be divided tentatively into two classes, those resulting from instabilities (ULF waves) and those produced by changes in macroscopic current systems. The data and their interpretations will be reviewed in order to illustrate the potential importance of observations in the synchronous orbit during the International Magnetospheric Study.

Coleman, P. J., Jr.↗
NASA NTRS2010

Dst Index in the 2008 GEM Modeling Challenge - Model Performance for Moderate and Strong Magnetic Storms

The GEM 2008 modeling challenge efforts are expanding beyond comparing in-situ measurements in the magnetosphere and ionosphere to include the computation of indices to be compared. The Dst index measures the largest deviations of the horizontal magnetic field at 4 equatorial magnetometers from the quiet-time background field and is commonly used to track the strength of the magnetic disturbance of the magnetosphere during storms. Models can calculate a proxy Dst index in various ways, including using the Dessler-Parker Sckopke relation and the energy of the ring current and Biot-Savart integration of electric currents in the magnetosphere. The GEM modeling challenge investigates 4 space weather events and we compare models available at CCMC against each other and the observed values of Ost. Models used include SWMF/BATSRUS, OpenGGCM, LFM, GUMICS (3D magnetosphere MHD models), Fok-RC, CRCM, RAM-SCB (kinetic drift models of the ring current), WINDMI (magnetosphere-ionosphere electric circuit model), and predictions based on an impulse response function (IRF) model and analytic coupling functions with inputs of solar wind data. In addition to the analysis of model-observation comparisons we look at the way Dst is computed in global magnetosphere models. The default value of Dst computed by the SWMF model is for Bz the Earth's center. In addition to this, we present results obtained at different locations on the Earth's surface. We choose equatorial locations at local noon, dusk (18:00 hours), midnight and dawn (6:00 hours). The different virtual observatory locations reveal the variation around the earth-centered Dst value resulting from the distribution of electric currents in the magnetosphere during different phases of a storm.

Rastaetter, Lutz↗
NASA NTRS2002

Timekeeping for the Space Technology 5 (ST-5) Mission

Space Technology 5, or better known as ST-5, is a space technology development mission in the New Millennium Program (NMP) and NASA s first experiment in the design of miniaturized satellite constellations. The mission will design, integrate and launch multiple spacecraft into an orbit high above the Earth s protective magnetic field known as the magnetosphere. Each spacecraft incorporates innovative technology and constellation concepts which will be instrumental in future space science missions. A total of three ST-5 spacecraft will be launched as secondary payloads into a highly elliptical geo-synchronous transfer orbit, and will operate as a 3-element constellation for a minimum duration of 90 days. In order to correlate the time of science measurements with orbit position relative to the Earth, orbit position in space (with respect to other objects in space) and/or with events measured on Earth or other spacecraft, accurate knowledge of spacecraft and ground time is needed. Ground time as used in the USA (known as Universal Time Coordinated or UTC) is maintained by the U.S. Naval Observatory. Spacecraft time is maintained onboard within the Command and Data Handling (C&DH) system. The science requirements for ST-5 are that spacecraft time and ground time be correlatable to each other, with some degree of accuracy. Accurate knowledge of UTC time on a spacecraft is required so that science measurements can be correlated with orbit position relative to the Earth, orbit position in space and with events measured on Earth or other spacecraft. The most crucial parameter is not the clock oscillator frequency, but more importantly, how the clock oscillator frequency varies with time or temperature (clock oscillator drift). Even with an incorrect clock oscillator frequency, if there were no drift, the frequency could be assessed by comparing the spacecraft clock to a ground clock during a few correlation events. Once the frequency is accurately known, it is easy enough to make a regular adjustment to the spacecraft clock or to calculate the correct ground time for a given spacecraft clock time. The oscillator frequency, however, is temperature dependent, drifts with age and is affected by radiation; hence, repeated correlation measurements are required.

Raphael, Dave↗
NASA NTRS1983

Magnetospheric currents

After outlining the constituent parts of the magnetospheric system, a historical review is presented of studies of the earth's magnetic field. It is noted that a connection between the aurora and variations in the magnetic field was first suggested by Halley in 1716. In discussing the magnetosphere, it is pointed out that the geomagnetic field can be thought of as being produced by a huge bar magnet embedded in the earth, with the axis of the magnet tilted away slightly from the earth's rotational axis. Attention is also given to the interplanetary magnetic field, to the relationship between the interplanetary magnetic field and the geomagnetic field, to convective flow, to field-aligned currents, and to Birkeland currents and auroral emissions. Various questions concerning the Birkeland currents are summarized.

Potemra, T. A.↗
DOE OSTI2020

Neutral Atom Imaging of the Solar Wind-Magnetosphere-Exosphere Interaction Near the Subsolar Magnetopause

Energetic neutral atoms (ENAs) created by charge-exchange of ions with the Earth's hydrogen exosphere near the subsolar magnetopause yield information on the distribution of plasma in the outer magnetosphere and magnetosheath. ENA observations from the Interstellar Boundary Explorer (IBEX) are used to image magnetosheath plasma and, for the first time, low-energy magnetospheric plasma near the magnetopause. These images show that magnetosheath plasma is distributed fairly evenly near the subsolar magnetopause; however, low-energy magnetospheric plasma is not distributed evenly in the outer magnetosphere. Simultaneous images and in situ observations from the Magnetospheric Multiscale (MMS) spacecraft from November 2015 (during the solar cycle declining phase) are used to derive the exospheric density. The ~11–17 cm –3 density at 10 R E is similar to that obtained previously for solar minimum. Thus, these combined results indicate that the exospheric density 10 R E from the Earth may have a weak dependence on solar cycle.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1990

Energetic neutral atoms: Imaging the magnetospheric ring current

Magnetospheric imaging is a new discipline whose goal is to make pictures of the energetic particle populations trapped in the magnetic field of Earth (or any other planet). This project demonstrated the technical feasibility and scientific validity of magnetospheric imaging using energetic neutral atoms (ENA) with the publication and quantitative analysis of the first ENA images ever obtained from space. ENA's are produced when singly-charged energetic (approximately 100 keV) trapped ions make an atomic collision with the neutral hydrogen atoms which boil of the top of the Earth's atmosphere. These hydrogen atoms suffuse the entire trapping volume of the magnetosphere. The energetic ion steals the electron from the atmospheric hydrogen, so the energetic ion is transformed into an energetic neutral atom with a velocity of several thousands of kilometers/second. Moreover, the new-born ENA preserves the velocity that the trapped ion had at the time of the collision. Consequently, any population of energetic ions emits ENA's.

Roelof, Edmond C.↗
NASA NTRS1975

Geomagnetic responses to the solar wind and the solar activity

Following some historical notes, the formation of the magnetosphere and the magnetospheric tail is discussed. The importance of electric fields is stressed and the magnetospheric convection of plasma and magnetic field lines under the influence of large-scale magnetospheric electric fields is outlined. Ionospheric electric fields and currents are intimately related to electric fields and currents in the magnetosphere and the strong coupling between the two regions is discussed. The energy input of the solar wind to the magnetosphere and upper atmosphere is discussed in terms of the reconnection model where interplanetary magnetic field lines merge or connect with the terrestrial field on the sunward side of the magnetosphere. The merged field lines are then stretched behind earth to form the magnetotail so that kinetic energy from the solar wind is converted into magnetic energy in the field lines in the tail. Localized collapses of the crosstail current, which is driven by the large-scale dawn/dusk electric field in the magnetosphere, divert part of this current along geomagnetic field lines to the ionosphere, causing substorms with auroral activity and magnetic disturbances. The collapses also inject plasma into the radiation belts and build up a ring current. Frequent collapses in rapid succession constitute the geomagnetic storm.

Svalgaard, L.↗
NASA NTRS2023

Mesoscale Phenomena and Their Contribution to the Global Response: A Focus on the Magnetotail Transition Region and Magnetosphere-Ionosphere Coupling

An important question that is being increasingly studied across subdisciplines of Heliophysics is “how do mesoscale phenomena contribute to the global response of the system?” This review paper focuses on this question within two specific but interlinked regions in Near-Earth space: the magnetotail’s transition region to the inner magnetosphere and the ionosphere. There is a concerted effort within the Geospace Environment Modeling (GEM) community to understand the degree to which mesoscale transport in the magnetotail contributes to the global dynamics of magnetic flux transport and dipolarization, particle transport and injections contributing to the storm-time ring current development, and the substorm current wedge. Because the magnetosphere-ionosphere is a tightly coupled system, it is also important to understand how mesoscale transport in the magnetotail impacts auroral precipitation and the global ionospheric system response. Groups within the Coupling, Energetics and Dynamics of Atmospheric Regions Program (CEDAR) community have also been studying how the ionosphere-thermosphere responds to these mesoscale drivers. These specific open questions are part of a larger need to better characterize and quantify mesoscale “messengers” or “conduits” of information—magnetic flux, particle flux, current, and energy—which are key to understanding the global system. After reviewing recent progress and open questions, we suggest datasets that, if developed in the future, will help answer these questions.

transition region↗
NASA NTRS1973

Magnetospheric plasma motion during a sudden commencement.

A sudden commencement occurred at 2348 UT on Feb. 15, 1967, when the ATS-1 satellite was about 2 hr past local noon at a geocentric distance of 6.6 earth radii. Plasma was observed by the Suprathermal Ion Detector first to flow in the antisolar direction, as expected, but then to flow westward, for about 2 min, at about 50 km/sec. Analysis of ground magnetograms suggests that the surprising westward flow, which must have involved an electric field of about 10 mV/m at 6.6 earth radii, resulted from the ionosphere's reaction to the sudden commencement. Beginning about 2 min before the start of the westward flow at ATS-1, ground magnetometers near the foot of the ATS-1 field line typically recorded magnetic-field deflections of about 70 gamma, to the northeast. Taking the ground observations, assuming a height-integrated Hall conductivity of 1 mho, and a standoff distance of 7.2 earth radii inferred from Explorer 33 solar-wind data, a magnetospheric electric field is derived which agrees in magnitude and direction with that required to produce the observed flow at ATS-1.

Lin, C.-A.↗
NASA NTRS1990

A model of the magnetospheric tail with current-free lobes

A model of the earth's tail field with no current density in its high latitude lobes is obtained as a modification of Tsyganenko's tail model. This is achieved by replacing Tsyganenko's current element with one in which the current density ends abruptly at a distance D from the central axis.

Stern, David P.↗
NASA NTRS1992

Is the earth's magnetotail balloon unstable?

In the past, the onset of magnetospheric substorms has been attributed to the plasma tearing mode instabilities. This paper investigates the ideal MHD ballooning instability of the near-and middle-tail magnetosphere region, as a first step toward determining whether it could trigger the tearing mode, by using the energy principle to investigate whether standard 2D tail models with the 'hard' ionospheric boundary condition are unstable to ballooning instability. Numerical results are presented for compressible ballooning modes that are symmetric about the center of the current sheet. It is shown that, for such a hard boundary condition, no reasonable magnetotail configuration exists that would be unstable to compressible symmetric ballooning but stable against interchange.

Lee, D.-Y.↗
NASA NTRS2012

What Properties of CMEs are Most Important for Space Weather?

Severe space weather is characterized by intense particle radiation from the Sun and major geomagnetic storm caused by magnetized solar plasmas arriving at Earth. Coronal mass ejections (CMEs) are key players in both these aspects. CMEs traveling at super-Alfv nic speeds drive fast-mode MHD shocks that create the high levels of particle radiation. When a CME arrives at Earth, the CME-associated magnetic fields reconnect with Earth s magnetopause fields resulting in solar plasma entry into the magnetosphere and a geomagnetic storm depending on the magnetic structure of the CME. Particle radiation starts affecting geospace as soon as the CMEs leave the Sun and the geospace may be immersed in the radiation for several days. On the other hand, the geomagnetic storm happens only upon CME arrival at Earth. The requirements for the production of particles and magnetic storms by CMEs are different in a number of respects: solar source location, CME magnetic structure, conditions in the ambient solar wind, and shock-driving ability of CMEs. Intense shocks arriving at Earth have additional space weather effects such as sudden impulse that shrinks the magnetosphere often exposing satellites in geosynchronous orbit to the solar wind and energetic storm particle events. This paper highlights these space weather effects using CME observations space and ground based instruments during of solar cycles 23 and 24.

Gopalswamy, Nat↗