Laboratory Experiments on Astrophysical Dust Analogs at NASA/MSFC
No abstract available
dust interstellar space↗
Engineering topics
Gallagher, Dennis L.
Publications and source records attributed to Gallagher, Dennis L..
Space Weather
This video provides a narrated exploration of the history and affects of space weather. It includes information the earth's magnetic field, solar radiation, magnetic storms, and how solar winds affect electronics on earth, with specific information on how space weather affects space exploration in the future.
Gallagher, Dennis L.↗
Space Weather
This slide presentation reviews the hazards and effects of space weather on earth and in space to humans and manmade systems.
Gallagher, Dennis L.↗
Analyzing Electric Field Morphology Through Data-Model Comparisons of the GEM IM/S Assessment Challenge Events
The storm-time inner magnetospheric electric field morphology and dynamics are assessed by comparing numerical modeling results of the plasmasphere and ring current with many in situ and remote sensing data sets. Two magnetic storms are analyzed, April 22,2001 and October 21-23,2001, which are the events selected for the Geospace Environment Modeling (GEM) Inner Magnetosphere/Storms (IM/S) Assessment Challenge (IMSAC). The IMSAC seeks to quantify the accuracy of inner magnetospheric models as well as synthesize our understanding of this region. For each storm, the ring current-atmosphere interaction model (RAM) and the dynamic global core plasma model (DGCPM) were run together with various settings for the large-scale convection electric field and the nightside ionospheric conductance. DGCPM plasmaspheric parameters were compared with IMAGE-EUV plasmapause extractions and LANL-MPA plume locations and velocities. RAM parameters were compared with Dst*, LANL-MPA fluxes and moments, IMAGE-MENA images, and IMAGE-HENA images. Both qualitative and quantitative comparisons were made to determine the electric field morphology that allows the model results to best fit the plasma data at various times during these events. The simulations with self-consistent electric fields were, in general, better than those with prescribed field choices. This indicates that the time-dependent modulation of the inner magnetospheric electric fields by the nightside ionosphere is quite significant for accurate determination of these fields (and their effects). It was determined that a shielded Volland-Stern field description driven by the 3-hour Kp index yields accurate results much of the time, but can be quite inconsistent. The modified Mcllwain field description clearly lagged in overall accuracy compared to the other fields, but matched some data sets (like Dst*) quite well. The rankings between the simulations varied depending on the storm and the individual data sets, indicating that each field description did well for some place, time, and energy range during the events, as well as doing less well in other places, times, and energies. Several unresolved issues regarding the storm-time inner magnetospheric electric field are discussed.
Liemohn, Michael W.↗
Plasmaspheric Drainage Plumes: Inner-Magnetospheric Coupling from the IMAGE/EUV Perspective
Plasmaspheric drainage plumes appear in the aftermath of periods of enhanced convection/erosion and are interpreted as a near-equatorial signature of the redistribution of thermal plasma along streamlines. Analysis of IMAGE/EUV observations from "FirstLight" through the end of calendar year 2002 reveals that for Kp greater than or equal to 3, there is an 84% probability of observing a plasmaspheric plume in EUV data. We present a statistical analysis of the geomagnetic conditions [Kp, Dst, and solar wind-induced electric field] associated with EUV plume observations. This analysis yields a peak in observational probability when Kp = 4 and Dst = -50 nT. Additionally, EUV pllume observations are associated with a solar wind-induced convection electric field at Earth [Ev, SM] characterized by bi-modal behavior with a positive mode peaked at approximately 4 m V(raised dot) m(sup -1) and a negative model that peaks at -2 mV (raised dot) m(sup -1). Analysis of the time rate of change of the plume-associated Ev, SM indicated that once the mechanism for plume formation is initiated, a slowly changing convection environment is required to allow for sufficient plume development prior to EUV detection.
Adrian, Mark L.↗
Is the Linear Mode Conversion Theory Viable for Generating Kilometric Continuum?
Kilometric Continuum (KC) usually exhibits a complicated banded radiation pattern observed in frequency time spectrograms. Can the number of bands, the frequency range over which the bands are observed, and their time variation be explained with Linear Mode Conversion Theory (LMCT) using realistic plasmapause models and Extreme Ultraviolet (EUV) plasmaspheric observations? In this paper we compare KC observations with simulated frequency emission bands based on LMCT for a number of cases. In LMCT the allowed frequency range across the equatorial plasmapause is restricted to frequencies much greater than the electron cyclotron frequency (fce) and less than the maximum plasma frequency in this region. Fce also determines the number of allowed bands in this range. Is the observed frequency range and number of bands consistent with the predications of LMCT? Can irregularities in the shape of plasmaspheric structures like notches be observed in the time variations of KC emissions? We will investigate these and other questions. Simulated radiation patterns will be generated by ray tracing calculations in the L-O mode from the radio window at the near equatorial plasmapause. The KC observations used in this study are from the Plasma Wave Instrument on the Geotail spacecraft and from the Radio Plasma Imager on the IMAGE spacecraft. The plasmasphere and plasmapause will be derived either from plasmasphere simulations, from images by the EUV imager on the IMAGE spacecraft, and by using empirical models. In situ plasma density measurements from a number of spacecraft will also be used in order to reconstruct the plasmasphere for these case studies.
Boardsen, Scott A.↗
Comparison of Two IRI plasmasphere Extensions with GPS-TEC Observations
Comparisons of two model results with Global Positioning System GPS-TEC measurements have been carried out for different latitudinal, solar activity, magnetic activity, diurnal and seasonal conditions. The models evaluated are the Global Core Plasma Model (GCPM-2000) and the IRI extension with Russian plasmasphere model (IRI*).Data of 23 observatories providing GPS-TEC and ionosonde data have been used. It is shown that IRI* plasmasphere electron density is greater than GCPM results by an order of magnitude at 6370 km altitude (one Earth's radius) with this excess growing to 2-3 orders of magnitude towards the GPS satellite altitude of 20000 km. Another source of model and GPS-TEC differences is a way of selection of the F2 layer peak parameters driving the models either with ITU-R (former CCIR) maps or ionosonde observations. Plasmasphere amendment to IRI improves accuracy of TEC model predictions because the plasmasphere contribution to the total TEC varies from 10% by daytime under quiet magnetic conditions to more than 50% by night under stormy conditions.
Gulyaeva, T. L.↗
Correlation Between Low Frequency Auroral Kilometric Radiation (AKR) and Auroral Structures
Auroral Kilometric Radiation (AKR) is a radio wave emission that has long been associated with auroral activity. AKR is normally observed in the frequency range from -60 - 600 kHz. Low frequency AKR (or LF-AKR) events are characterized as a rapid extension of AKR related emissions to 30 kHz or lower in frequency for typically much less than 10 minutes. LF-AKR emissions predominantly occur within a frequency range of 20 kHz - 30 kHz, but there are LF-AKR related emissions that reach to a frequency of 5 kHz. This study correlates all instances of LF-AKR events during the first four years of observations from the IMAGE spacecraft's Radio Plasma Imager (WI) instrument with auroral observations from the wideband imaging camera (WIC) onboard IMAGE. The correlation between LF-AKR occurrence and WIC auroral observations shows that in the 295 confirmed cases of LF-AKR emissions, bifurcation of the aurora is seen in 74% of the cases. The bifurcation is seen in the dusk and midnight sectors of the auroral oval, where AKR is believed to be generated. The polarization of these LF-AKR emissions has yet to be identified. Although LF-AKR may not be the only phenomena correlated with bifurcated auroral structures, bifurcation will occur in most instances when LF-AKR is observed. The LF-AKR emissions may be an indicator of specific auroral processes sometimes occurring during storm-time conditions in which field-aligned density cavities extend a distance of perhaps 5-6 RE tailward from the Earth for a period of 10 minutes or less.
Paxamickas, Katherine A.↗
When Earth Songs Filled the Void of Space
Before the late 50's we had the planets, our Sun, the stars, galaxies, spectacular clouds of dust and very little else in our universe. There was evidence for a highly tenuous "sea" of dust in interstellar space, but little else. Space was empty above the ionized gases of our upper atmosphere, a little like there was no color in the world before the 40's. The clues were there to think otherwise, however, and in the late 50's and early 60's a few researchers dared to challenge the conventional ideas about space. It was a time of discovery and, with our new ability to fly in space, a time that launched a new science. Today that science makes it possible to literally see some of the plasmas that populate near-Earth space, which are now known to exist everywhere.
Gallagher, Dennis L.↗
Jupiter: The Solar System's Giant
At more than 10 times the size of the Earth, Jupiter is the largest planet in the solar system. Although not quite large enough to be a sun, it still has its own system of moons and rings. It's huge magnetic field and fast rotation make Jupiter both the most interesting planet and the most dangerous. From the sulfur volcanoes of Io to the frozen water ice ocean of Europa, Jupiter "rocks". Come experience what NASA has learned about the giant planet
Gallagher, Dennis L.↗
Integration of the Empirical Exospheric GCPM Plasma Model into IRI
The Global Core Plasma Model (GCPM) is an empirical description of typical thermal magnetospheric plasma densities in the plasmasphere, plasma trough, and polar cap. The GCPM makes use of the International Reference Ionosphere (IRI) for low altitudes. Densities are continuous and smooth. Plasmaspheric ion composition is also included in the GCPM. For the purpose of supporting the ionospheric community, the densities derived in the GCPM for high altitudes will be expressed as an extension of the IRI. The GCPM exospheric extension of IRI improves the topside densities and provides typical thermal plasma densities for the plasmasphere, trough, and polar cap. The GCPM is modular, having been designed for continued improvement as statistical density and composition measurements become available.
Gallagher, Dennis L.↗
The Storm-Time Plasmasphere as Seen by the Extreme Ultraviolet (EUV) Imager on the IMAGE Spacecraft
Many years of ground and space observations of the plasmasphere have established a basic understanding of the physics of these plasmas in the inner magnetosphere. However, many questions remain. The EUV Instrument on the IMAGE spacecraft is now providing the first ever global pictures of thermal helium in the plasmasphere. Detached plasma, the sunward extending convection tail, a night-time interior plasmaspheric density cavity, and strong azimuthal plasmaspheric structures are all being revealed. What are the properties of these structures? How do they evolve? What is their relationship to magnetic storms and other plasma populations? These are some of the questions that define the state of plasmaspheric physics, to which IMAGE is now contributing answers. The graphic evidence and preliminary analysis of these features will be presented and discussed.
Gallagher, Dennis L.↗
IMAGE Software Suite
The IMAGE Mission is generating a truely unique set of magnetospheric measurement through a first-of-its-kind complement of remote, global observations. These data are being distributed in the Universal Data Format (UDF), which consists of data, calibration, and documentation. This is an open dataset, available to all by request to the National Space Science Data Center (NSSDC) at NASA Goddard Space Flight Center. Browse data, which consists of summary observations, is also available through the NSSDC in the Common Data Format (CDF) and graphic representations of the browse data. Access to the browse data can be achieved through the NSSDC CDAWeb services or by use of NSSDC provided software tools. This presentation documents the software tools, being provided by the IMAGE team, for use in viewing and analyzing the UDF telemetry data. Like the IMAGE data, these tools are openly available. What these tools can do, how they can be obtained, and how they are expected to evolve will be discussed.
Gallagher, Dennis L.↗
Global Core Plasma Model
Abstract. The Global Core Plasma Model (GCPM) provides, empirically derived, core plasma density as a function of geomagnetic and solar conditions throughout the inner magnetosphere. It is continuous in value and gradient and is composed of separate models for the ionosphere, the plasmasphere, the plasmapause, the trough, and the polar cap. The relative composition of plasmaspheric H+, He+, and O+ is included in the GCPM. A blunt plasmaspheric bulge and rotation of the bulge with changing geomagnetic conditions is included. The GCPM is an amalgam of density models, intended to serve as a framework for continued improvement as new measurements become available and are used to characterize core plasma density, composition, and temperature.
Gallagher, Dennis L.↗