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Sandel, B. R.

Publications and source records attributed to Sandel, B. R..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Imaging Thermal He(+)in Geospace from the Lunar Surface

By mass, thermal plasma dominates near-earth space and strongly influences the transport of energy and mass into the earth's atmosphere. It is proposed to play an important role in modifying the strength of space weather storms by its presence in regions of magnetic reconnection in the dayside magnetopause and in the near to mid-magnetotail. Ionospheric-origin thermal plasma also represents the most significant potential loss of atmospheric mass from our planet over geological time. Knowledge of the loss of convected thermal plasma into the solar wind versus its recirculation across high latitudes and through the magnetospheric flanks into the magnetospheric tail will enable determination of the mass balance for this mass-dominant component of the Geospace system and of its influence on global magnetospheric processes that are critical to space weather prediction and hence to the impact of space processes on human technology in space and on Earth. Our proposed concept addresses this basic issue of Geospace dynamics by imaging thermal He(+) ions in extreme ultraviolet light with an instrument on the lunar surface. The concept is derived from the highly successful Extreme Ultraviolet imager (EUV) flown on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft. From the lunar surface an advanced EUV imager is anticipated to have much higher sensitivity, lower background noise, and higher communication bandwidth back to Earth. From the near-magnetic equatorial location on the lunar surface, such an imager would be ideally located to follow thermal He(+) ions to high latitudes, into the magnetospheric flanks, and into the magnetotail.

Gallagher, D. L.↗
NASA NTRS2006

Imaging Thermal He(+) from the Lunar Surface

Extreme ultraviolet observations of He(+) ions by the EUV instrument on the IMAGE spacecraft have dramatically improved our ability to observe plasmasphere dynamics in the inner magnetosphere. These primarily high latitude observations have revealed the phenomenology of thermal density structures and continue to lead us toward a more complete understanding of inner magnetospheric electric fields and plasmaspheric refilling. Recent analyses have brought attention to the disposition of thermal plasma eroded from the plasmasphere and convected into the outer dayside magnetosphere. The extent to which this plasma is lost into the solar wind or recirculated across the polar cap or through the magnetospheric flanks is an important outstanding question that relates to the influence this plasma has on space weather processes in Geospace. A concept for implementation of enhanced EUV observations from the lunar surface to resolve questions about the global circulation of He(+) plasma in the magnetosphere will be presented. The instrument and science package subsystem elements, including anticipated component capabilities and limitations will be discussed. Attention will also be given to the potential impact of dust contamination.

Gallagher, D. L.↗
NASA NTRS2003

Plasmaspheric Mass Loss and Refilling as a Result of a Magnetic Storm

Using the sounding measurements from the radio plasma imager on IMAGE, and a plasma density inversion algorithm, we derive the plasma density profiles along the magnetic field in a few L-shells every 14 hours at magnetic local noon before, during, and after the March 31,2001 magnetic storm. An empirical model of the plasmaspheric plasma density distribution is derived as a reference using the measurements before the storm. During the storm, the equatorial plasma was substantially depleted in a range of L-shells. The flux tubes were refilled after the storm. The filling ratio, the equatorial plasma density normalized by its quiet-time value before the storm, is introduced to assess the time evolution of the depletion and refilling processes. The depletion, more than two thirds of the quiet time content, appeared to occur rather quickly after the storm onset, as determined by the limited temporal resolution of the measurements. The refilling proceeded, although more slowly than the depletion process, significantly faster than the theoretical prediction of a 3-day time scale. Dynamic structures are observed in situ and confirmed by the extreme ultraviolet imager (EUV) measurements.

Reinisch, B. W.↗
NASA NTRS2003

IMAGE Observations of Plasmasphere/Ring Current Interactions

Evidence has been found in IMAGE observations that overlap of the plasmasphere and the ring current may lead to enhanced loss of plasma into the ionosphere. It has long been anticipated that this mixing of plasma leads to coupling and resulting consequences on both populations. Wave generation, pitch angle scattering, and heating are some of the consequences that are anticipated. IMAGE plasmasphere ring current, and auroral observations will be presented and used to explore these interactions and their effects.

Gallagher, D. L.↗
NASA NTRS2002

The Geology of Comet 19/P Borrelly

The Deep Space One spacecraft flew by Comet 19P/Borrelly on September 22, 2001 and returned a rich array of imagery with resolutions of up to 48 m/pixel. These images provide a window into the surface structure, processes, and geological history of a comet. Additional information is contained in the original extended abstract.

Britt, D. T.↗
NASA NTRS2002

Plasmaspheric Density Troughs: Global IMAGE EUV Observations and Analysis via Global Core Plasma Modeling

To date, the IMAGE EUV camera has observed several plasmaspheric density trough features inside the plasmapause under a wide range of geomagnetic activity. From the perspective of EUV, a density trough feature appears as a channel of diminished pixel counts which spans a width of L-shell (DELTA L) and magnetic local time (MLT) inside the plasmapause. Plasmaspheric density troughs are found to be morphologically complex possessing considerable spatial and temporal variability. We present an analysis of the evolution of trough DELTA L and MLT extent as functions of associated D (sub ST) and K (sub p) history. Trough features range in size from 0.16 less than or equal to DELTA L less than or equal to 1.2 with azimuthal extent from 1500 less than or equal to MLT less than or equal to 1200. All cases of plasmaspheric density troughs studied to date appear to have evolved as a result of the inner edge of the afternoon/evening plasma drainage plume being wrapped around through the nightside plasmasphere. The structure of plasmaspheric density trough features is further probed by analyzing simulated EUV images produced by forward modeling artificially introduced regions of depleted density into both static and dynamic global core plasmaspheric models. Forward modeling suggests that (1) L-shell refilling of density troughs during storm recovery can be modeled as filling from the ionosphere toward the equator (i.e., bottom-up refilling), and (2) that an erosion process is operating within flux tubes beyond the outer L-shell wall of the observed density troughs.

Adrian, M. L.↗
NASA NTRS2002

Empty Flux Tubes and Plasmasphere Refilling as Seen by IMAGE

When a plasmaspheric flux tube is empty, what plasma is actually missing? When a flux tube refills, where does the plasma accumulate first? How long does it take to refill a flux tube to a level that is essentially saturated? Owing to the observational difficulties of measuring the distribution of plasmaspheric plasma along a flux tube, these questions have remained unanswered over many decades of study since discovery of the plasmasphere. They are important questions, because of the role that plasmaspheric plasma plays in collisional losses of higher energy populations, in modifying instabilities for wave-particle interactions, and in influencing the transport of energy through plasma waves. The Extreme Ultraviolet Imager and the Radio Plasma Imager on the IMAGE Mission are providing new, critical observations of the dynamic outer plasmasphere where convective erosion and refilling dominate. Latitudinal density profiles along a single L-shell from BPI confirm earlier indications of a mid-latitude transition between the altitude organized structure of the ionosphere and L-shell organized plasmasphere. Emptied flux tubes often mean empty only above about 1 Re in altitude or below plus or minus 40 degrees in magnetic latitude. Refilling to nearly saturated levels is found to take much less than that previously found necessary to complete the process. The observations behind these conclusions and the new light brought to plasmaspheric refilling will be discussed.

Adrian, M. L.↗
NASA NTRS2002

Plasmaspheric Erosion via Plasmasphere Coupling to Ring Current Plasmas: EUV Observations and Modeling

During a geomagnetic storm on 24 May 2000, the IMAGE Extreme Ultraviolet (EUV) camera observed a plasmaspheric density trough in the evening sector at L-values inside the plasmapause. Forward modeling of this feature has indicated that plasmaspheric densities beyond the outer wall of the trough are well below model expectations. This diminished plasma condition suggests the presence of an erosion process due to the interaction of the plasmasphere with ring current plasmas. We present an overview of EUV, energetic neutral atom (ENA), and Far Ultraviolet (FUV) camera observations associated with the plasmaspheric density trough of 24 May 2000, as well as forward modeling evidence of the lie existence of a plasmaspheric erosion process during this period. FUV proton aurora image analysis, convolution of ENA observations, and ring current modeling are then presented in an effort to associate the observed erosion with coupling between the plasmasphere and ring-current plasmas.

Adrian, M. L.↗
NASA NTRS2002

IMAGE-EUV Observation of Large Scale Standing Wave Pattern in the Nightside Plasmasphere

We present analyses of a nightside plasmaspheric pattern of bifurcated, filamentary He(+) 30.4-nm emission enhancements observed by IMAGE EUV between approximately 19:40-22:13 UT on 28 June 2000 that indicate the presence of a large-scale, global ULF standing wave pattern. Analysis of coincident IMAGE magnetometer chain data reveals that these ULF waves extend across the magnetic latitude-longitude range of the chain and possess multiple spectral features between 0.6-5-mHz (3-30 minute period). Additionally, analysis of ACE SWE data reveals similarly structured spectral components in the solar wind. Collectively, these analyses lead to the conclusion that the observed large-scale ULF wave pattern is the result of solar wind pressure pulses 'ringing' the inner-magnetosphere.

Six, N. Frank↗
NASA NTRS2001

Multiple Radially Aligned Plasmaspheric Structures as Evidence of Standing Hydromagnetic Waves: IMAGE EUV Observations and Forward Modeling

The IMAGE EUV imager has observed several instances where the outer plasmasphere is populated by multiple radially aligned structures resembling "plasmaspheric fingers". The observation of these plasmaspheric structures suggests the presence of an azimuthal standing hydromagnetic wave mode. Eiganmodes appear to explain finger-like. nearly radial density structures that sometimes divide into two structures with increasing radial distance. The implication is of boundaries at fixed local times, which results in a widening "box" in which standing waves are developed. The structures also suggest a single driving frequency for the source of the waves. We present EUV observations of plasmaspheric fingers observed on August 2000 as well as plasmaspheric modeling of azimuthal wave modes in an effort to quantify the origin of these observed structures

Gallagher, D. L.↗
NASA NTRS2001

The Large-Scale Plasmaspheric Density Trough Associated With the 24 May 2000 Geomagnetic Storm: IMAGE EUV Observations and Global Core Plasma Modeling

The IMAGE EUV imager observed a plasmaspheric density, trough in association with a geomagnetically active period on 24 May 2000. In EUV, this density, trough appears as an Archimedes spiral extending from Earth's shadow to approximately 1900 MLT. We present an analysis of this density trough using simulated EUV images, Observational EUV images are subjected to edge analysis to establish the plasmapause L-shell and the location of the density trough in terms of L-shell, MLT extent, and radial width. The plasmaspheric density distribution is modeled using both static and dynamic models for the plasmasphere. The background plasmasphere is then numerically simulated using the 4-parameter plasmaspheric density model contained within the Global Core Plasma Model (GCPM) and the Dynamic Global Core Plasma Model (DGCPM). Simulated EUV images of the model plasmasphere are produced once an artificial density, depletion, matching the observed MLT extent and width, has been removed. Once the azimuthal extent and width of the trough have been simulated, the depth of the artificial density depletion is iteratively adjusted to produce simulated EUV images that approximate observation. The results of this analysis and discussion of possible origins for this density trough will be presented.

Adrian, M. L.↗
NASA NTRS2000

IMAGE EUV Observations and Modeling of the Plasmaspheric Density Trough Associated with the 24 May 2000 Geomagnetic Storm

The IMAGE EUV imager observed a plasmaspheric density trough in association with a geomagnetically active period on 24 May 2000. At EUV wavelengths, this density trough appeared as an Archimedes spiral extending from Earth's shadow to approximately 1800 MLT. We present an analysis of this density trough using simulated EUV images. Observational EUV images are subjected to edge analysis to establish the plasmapause L-shell and the location of the density trough in terms of L-shell, MLT extent, and radial width. The plasmaspheric density distribution is modeled using both static and dynamic models for the plasmasphere. The background plasmasphere is then numerically simulated using the 4-parameter plasmaspheric density model contained within the Global Core Plasma Model (GCPM) [Gallagher et al., 20001 and the Dynamic Global Core Plasma Model (DGCPM). Simulated EUV images of the model plasmasphere are produced once an artificial density depletion, matching the observed MLT extent and width, has been removed. Once the azimuthal extent and width of the trough have been simulated, the depth of the artificial density depletion is iteratively adjusted to produce simulated EUV images that approximate observation. The results of this analysis and discussion of possible origins for this density trough will be presented.

Adrian, M.L.↗
NASA NTRS1999

The Plasmasphere as "Seen" by the IMAGE Mission

The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) is the first mission designed exclusively to remotely measure the magnetosphere. As such, it will reveal the ring current, plasmasphere, polar cusp, and magnetopause as whole extended, interacting systems. For the first time, our impressions of the global magnetosphere, synthesized through many years of whistler and in situ measurement, will be replaced by images. The overall morphology of each system of plasma and the correspondence of changes between them in response to the sun and solar wind will become available. The Extreme Ultraviolet Imager (EUV) and the Radio Plasma Imager (RPI) are the two IMAGE instruments which will remotely measure and image the plasmasphere. What we expect to "see" from these instruments and how it may be interpreted is the subject of this presentation. The EUV instrument includes three optical cameras, with an almost 90 degree field of view, transverse to the spin axis. EUV is designed to see He+ ions in resonantly scatter solar light at 30.4rim. The IMAGE spacecraft will spin with a period of about 2 minutes, with its spin axis parallel to the orbit normal. The IMAGE orbit will be highly inclined, with a high latitude apogee at a geocentric distance of 8RE and perigee of about 1.2RE. The normal observing integration time of 10 minutes will easily see to the outer edge of the plasmasphere. The RPI instrument makes use of three orthoganal dipole antennas: two in the spin plane with a tip-to-tip length of 500m and one along the spin axis with a length of 20 meters. Using coded pulse transmissions, the RPI instrument will broadcast from 3kHz to 3MHz. With one minute resolution, plasma densities from about 0.1 cm(exp -3) to 100,000 cm(exp -3), along with line-of-sight bulk velocities and locations, will be obtained from all returned radio wave signals. When transmitting from the high latitude magnetospheric cavity, RPI will measure density profiles for the major plasma structures in the magnetosphere, including the magnetopause, polar cusp, and plasmasphere. RPI should also see isolated density irregularities and possibly the plasma sheet. Observations The EUV instrument will return line-of-sight integrated images through the optically thin helium medium of the plasmasphere and magnetosphere. A variety of techniques have been suggested for the translation of the images into physically useful data, such as plasmapause location and three dimensional density distribution. The RPI instrument will return quantitative density values and line-of-sight velocity as a function of position along reflecting wave propagation paths. How they may be used individually and together to study plasmaspheric dynamics and global structure will be discussed. Attention will also be given to the data products and how access to IMAGE data will be provided by the IMAGE team and the NSSDC.

Gallagher, D. L.↗
NASA NTRS1995

Comparison between solar wind latitude distribution derived from Lyman-alpha observations and Ulysses measurements

The all-sky interplanetary Lyman-alpha pattern is sensitive to the latitude distribution of the solar wind because of destruction of neutral H by charge-exchange with solar wind protons. Lyman-alpha intensities recorded by Prognoz 5 and 6 in 1976 in a few parts of the sky were demonstrating a decrease of solar wind mass flux by about 30 % from equator to pole, when assuming a sinusoidal variation of this mass flux (harmonic distribution). A new analysis with a discrete variation with latitude has shown a decrease from 0 to 30 deg and then a plateau of constant mass flux up to the pole. This distribution bears a striking resemblance with Ulysses in-situ measurements, showing a clear similarity at 19 years interval. The Ulysses measurements were then used as a model input to calculate an all-sky Lyman-alpha pattern, either with a discrete model or with a harmonic solar wind variation with the same Ulysses equator-to-pole variation. There are conspicuous differences between the two Lyman-alpha patterns, in particular in the downwind region which are discussed in the context of future all-sky measurements with SWAN experiment on SOHO.

Quemarais, E.↗
NASA NTRS1995

Lyman alpha emissions in the outer heliosphere

Since 1993, the Ultraviolet Spectrometers aboard both Voyager 1 and 2, were used to study the Ly-alpha glow pattern backscattered by neutral hydrogen atoms at great distance from the sun. When compared to a radiative transfer calculation for an unperturbed interstellar hydrogen flow into the solar system, the data present an excess of intensity seen in the direction of the incoming interstellar wind. An absolute estimate of this Lyman alpha intensity yields 10 to 15 Rayleighs for each spacecraft. We discuss the possibility that this excess is caused by a gradient of hydrogen at large distance from the Sun due to the filtration of interstellar hydrogen when crossing the heliopause. Comparisons with results from the Baranov-Malama model of neutral-plasma coupling at the heliopause are presented. The data yield a range of possible values for the hydrogen gradient which may be used to infer the location of the heliopause.

Quemerais, E.↗
NASA NTRS1995

New analysis of the Voyager UVS H Lyman-alpha emission of Saturn

The limb to limb Lyman-alpha reflectivities observed with the Voyager ultraviolet spectrometer (UVS) instruments during the fly-by of Saturn are reanalyzed using a revised H Lyman-alpha sensitivity for the Voyager 1 instrument. The new sensitivity reconciles the measured intensities to those of Voyager 2 and gives a coherent set of data. To fit the UV airglow observations, four sources are considered: (1) H resonance and H2 Rayleigh scattering of solar Lyman-alpha radiation, (2) the interplanetary Lyman-alpha radiation, (3) a possible internal source of unknown origin, (4) the possibility of atmospheric turbulence recently proposed to explain the Lyman-alpha bulge of Jupiter. The analysis supports neither a dominant collisional excitation source for the UV emissions nor the presence of strong atmospheric turbulence. The best fit, in terms of brightness but also in terms of shape of the limb to limb profile (that is to say independent on the absolute calibrations), is obtained for pure resonance and Rayleigh scattering of solar and interstellar wind line in an atmosphere enriched in atomic hydrogen up to three times the standard model. Influx of water from the rings of Saturn may provide a means for producing such enhanced H densities in the upper atmosphere.

Jaffel, L. Ben↗