Engineering topics

Spann, J. F.

Publications and source records attributed to Spann, J. F..

53 records · Page 3

NASA NTRS1999

Magnetospheric Response to the Arrival of the Shock Wave in Front of the Magnetic Cloud of January 10, 1997

We are Studying the magnetic cloud event of January 6 - 11, 1997. Specifically, we have investigated the response of the magnetosphere to the shock wave in front of the magnetic cloud on January 10, 1997 using data from WIND, GEOTAIL and POLAR spacecraft as well as ground magnetometer data. The WIND spacecraft, which was located as about 104 Re upstream from the Earth (85.1, -55.2, -22.1) Re(sub GSM), observed the arrival of the shock wave front at 0050 UT. Geotail was located at the equatorial magnetopause (approx. 8.7 Re, 10.7 MLT, -7.46 MLAT), while POLAR was located in the northern dawn sector above the auroral zone at 8.4 Re, 6.1 MLT and 61.1 MLAT. A magnetic signature was nearly simultaneously observed at about 0104 UT at the POLAR and Geotail spacecraft. The Geotail spacecraft entered from the magnetosphere into the magnetosheath. Particle density increases were observed on WIND and Geotail, but not on POLAR. Two instruments on the Polar spacecraft (TIDE and TIMAS) actually observed a slight reduction in energy, density and temperature. The UV aurora shows a dawnside intensification. The shock wave did not cause an auroral substorm and therefore was not geoeffective.

Wuest, M.↗

NASA NTRS1999

Global Observations of Poleward Moving Aurora on the Dayside

Auroral arcs found at high latitude that move poleward from the nominal dayside oval, also known as poleward moving auroral forms been extensively studied from ground-based all-sky camera and meridian scanning photometric measurements. These auroral forms are thought to be he ionospheric signature of dayside reconnection processes at the magnetopause and therefore important for determining the relationship between the solar wind interplanetary magnetic field (IMF) and the location and size of the reconnection region. The large-scale picture of these dayside phenomenon derived from satellite imagery, however, has not been fully developed. Observations from the Polar Ultraviolet Imager (UVI) have sufficient time and spatial resolution to examine the longitudinal extent and motion of high-latitude arcs that extend across several hours of magnetic local time in the dayside aurora. We discuss the size and evolution of moving dayside aurorae in relation to the solar wind IMF orientation. We show also that the intensity of these auroral features is related to both solar wind pressure pulses and nightside auroral intensifications.

Brittnacher, M. J.↗

NASA NTRS1999

Magnetotail Plasma Signatures of Pseudobreakups and Substorms

Using Polar/UVI global images, we have identified a period of successive minor auroral activations during which WIND was making a perigee pass through the near-Earth magnetotail. On the basis of images, these auroral brightenings are interpreted to be pseudobreakups due to the lack of significant global expansion. Large magnetic by the WIND spacecraft show a nearly one-to-one correspondence auroral intensifications. During intervals of large field auroral brightenings, energized ions have an Earthward velocity energized electrons generally remain isotropic. Closer inspection ion distribution functions indicate that the high velocity moments are not due to convective flows. Rather, the plasma is composed of a component and a stagnate cold component. We also trace the observed by WIND backwards in time to determine the source regions for the particles. Based upon these observations, we find that to zeroth order there is no difference in the behavior of the plasma during as compared to substorm expansive phase events.

Fillingim, M. O.↗

NASA NTRS1999

A Laboratory Study of the Charging/Discharging Mechanisms of a Dust Particle Exposed to an Electron Beam

The interaction of micron sized particles or "dust particles" with different space and planetary environments has become an important area of research. One particular area of interest is how dust particles interact with plasmas. Studies have shown that charged dust particles immersed in plasmas can alter plasma characteristics, while ions and electrons in plasmas can affect a particle's potential and thereby, its interaction with other particles. The basis for understanding these phenomena is the charging mechanisms of the dust particle, specifically, how the particle's charge and characteristics are affected when exposed to ions and electrons. At NASA Marshall Space Flight Center, a laboratory experiment has been developed to study the interaction of dust particles with electrons. Using a unique laboratory technique known as electrodynamic suspension, a single charged particle is suspended in a modified quadrupole trap. Once suspended, the particle is then exposed to an electron beam to study the charging/discharging mechanisms due to collisions of energetic electrons. The change in the particle's charge, approximations of the charging/discharging currents, and the charging/discharging yield are calculated.

Venturini, C. C.↗

NASA NTRS1999

On the Relationship of Interplanetary Pressure Pulses and Subsequent Auroral Activity

The relation between interplanetary pressure pulses and subsequent auroral breakup is examined using over 70 cases from 1997 to 1999. A solar wind-magnetosphere coupling parameter (based on Bargatze et al., Solar Wind-Magnetosphere Coupling, Terra Scientific Publishing Co., p. 101- 109, 1986) is used to correlate the amount of energy stored in the magnetospheric to the time delay for auroral activity relative to the SW pressure enhancement.

Spann, J. F.↗

NASA NTRS1998

Relationship of Topside Ionospheric Ion Outflows to Auroral Forms and Precipitation, Plasma Waves, and Convection Observed by Polar

The POLAR satellite often observes upflowing ionospheric ions (UFIs) in and near the aurora] oval on southern perigee (approx. 5000 km altitude) passes. We present the UFI features observed by the thermal ion dynamics experiment (TIDE) and the toroidal imaging mass angle spectrograph (TIMAS) in the dusk-dawn sector under two different geomagnetic activity conditions in order to elicit their relationships with auroral forms, wave emissions, and convection pattern from additional POLAR instruments. During the active interval, the ultraviolet imager (UVI) observed a bright discrete aurora on the duskside after the substorm onset and then observed a small isolated aurora form and diffuse auroras on the dawnside during the recovery phase. The UFIs showed clear conic distributions when the plasma wave instrument (PWI) detected strong broadband wave emissions below approx. 10 kHz, while no significant auroral activities were observed by UVI. At higher latitudes, the low-energy UFI conics gradually changed to the polar wind component with decreasing intensity of the broadband emissions. V-shaped auroral kilometric radiation (AKR) signatures observed above -200 kHz by PWI coincided with the region where the discrete aurora and the UFI beams were detected. The latitude of these features was lower than that of the UFI conics. During the observations of the UFI beams and conics, the lower-frequency fluctuations observed by the electric field instrument were also enhanced, and the convection directions exhibited large fluctuations. It is evident that large electrostatic potential drops produced the precipitating electrons and discrete auroras, the UFI beams, and the AKR, which is also supported by the energetic plasma data from HYDRA. Since the intense broadband emissions were also observed with the UFIs, the ionospheric ions could be energized transversely before or during the parallel acceleration due to the potential drops.

Hirahara, M.↗

NASA NTRS1998

Initial Response and Complex Polar Cap Structures of the Aurora in Response to the January 10, 1997 Magnetic Cloud

On January 10, 1997, a magnetic cloud originating at the Sun was incident on the Earth. The initial disturbance to the magnetosphere, as reflected in the activities of the aurora, was measured by the Ultraviolet Imager on the Polar Spacecraft. During this event we have observed the development of several unusual unique auroral forms that to our knowledge are unexplained in current models and theories. The observations were made on a global scale with unprecedented spatial and temporal resolution. The first activation of the aurora at local noon occurred within minutes of the arrival of the shock at 0107 UT. The substorm onset was observed at 0334 UT. During the intervening time significant polar cap precipitation occurred.

Spann, J. F.↗

NASA NTRS1998

Auroral Observations from the POLAR Ultraviolet Imager (UVI)

Because of the importance of the auroral regions as a remote diagnostic of near-Earth plasma processes and magnetospheric structure, spacebased instrumentation for imaging the auroral regions have been designed and operated for the last twenty-five years. The latest generation of imagers, including those flown on the POLAR satellite, extends this quest for multispectral resolution by providing three separate imagers for the visible, ultraviolet, and X ray images of the aurora. The ability to observe extended regions allows imaging missions to significantly extend the observations available from in situ or groundbased instrumentation. The complementary nature of imaging and other observations is illustrated below using results from tile GGS Ultraviolet Imager (UVI). Details of the requisite energy and intensity analysis are also presented.

Germany, G. A.↗

NASA NTRS1998

The Nightside Auroral Gap: Implications for Magnetosphere-Ionosphere Coupling in the Midnight Auroral Zone

We present observations of a new synoptic scale feature of the nightside aurora identified by the Polar Ultraviolet Imager (UVI) in which a well defined segment of the pre-midnight auroral oval exhibits significantly reduced auroral luminosity in the atomic oxygen and Lyman-Birge-Hopfield (LBH) emission bands in comparison to adjacent auroral activity. This gap in the nightside aurora is typically observed in the 2200-2400 MLT sector and spans 1.0-1.5 hours in local time (710-1100 km). The energy flux ($\rm erg$ $\rm cm'{-2}$ $\rm s'{-1}$) is shown to be lower by as much as a factor of four in the nightside gap region in comparison to the adjacent auroral activity. The appearance of the nightside gap does not depend on substorm phase. However, substorm intensifications are often observed on either side of the nightside gap which remains relatively inactive. Moreover, auroral breakups sometimes develop within the nightside gap, indicating that this feature may have dynamical implications for substorm onset location.

Chua, D. H.↗

NASA NTRS1998

Coincident UVI and Wind Observations of Pseudo-Breakups

Using images taken by the Ultraviolet Imager (UVI) onboard the Polar spacecraft, we identify periods of pseudo-breakup activity coincident with perigee passes of the WIND spacecraft through the magnetotail. Previous studies have shown that from both observations on the ground and in the magnetotail there is very little difference phenomenologically between substorm onset and pseudo-breakups except for the degree of localization and the absence of global expansion. This raises the question of what prevents a pseudo-breakup from expanding globally. For the time intervals studied, we find a high correlation between pseudo-breakups and short-lived particle flux enhancements in the magnetotail. The velocity distribution of the plasma during some of these flux enhancements are indicative of bursty bulk flows.

Fillingim, M. O.↗

NASA NTRS1998

Solar Wind-Magnetosphere Coupling Influences on Pseudo-Breakup Activity

Pseudo-breakups are brief, localized aurora[ arc brightening, which do not lead to a global expansion, are historically observed during the growth phase of substorms. Previous studies have demonstrated that phenomenologically there is very little difference between substorm onsets and pseudo-breakups except for the degree of localization and the absence of a global expansion phase. A key open question is what physical mechanism prevents a pseudo-breakup form expanding globally. Using Polar Ultraviolet Imager (UVI) images, we identify periods of pseudo-breakup activity. Foe the data analyzed we find that most pseudo-breakups occur near local midnight, between magnetic local times of 21 and 03, at magnetic latitudes near 70 degrees, through this value may change by several degrees. While often discussed in the context of substorm growth phase events, pseudo-breakups are also shown to occur during prolonged relatively inactive periods. These quiet time pseudo-breakups can occur over a period of several hours without the development of a significant substorm for at least an hour after pseudo-breakup activity stops. In an attempt to understand the cause of quiet time pseudo-breakups, we compute the epsilon parameter as a measure of the efficiency of solar wind-magnetosphere coupling. It is noted that quiet time pseudo-breakups occur typically when epsilon is low; less than about 50 GW. We suggest that quiet time pseudo-breakups are driven by relatively small amounts of energy transferred to the magnetosphere by the solar wind insufficient to initiate a substorm expansion onset.

Fillingim, M. O.↗

NASA NTRS1998

Magnetospheric Response to the Arrival of the Shock Wave in Front of the Magnetic Cloud Event of January 10,1997

We are studying the magnetic cloud event of January 6-11, 1997. Specifically, we have investigated the response of the magnetosphere to the shock wave in front of the magnetic cloud on January 10, 1997 using data from WIND, GEOTAIL and POLAR spacecraft as well as ground magnetometer data. The WIND spacecraft, which was located at about 100 Re upstream from the Earth, observed the arrival of the shock wave front at 005OUT. Geotail was located at the equatorial magnetopause (approx. 8.7 Re), while POLAR was located in the northern dawn sector at 8.4 Re, 6.1 MLT and 61.1 MLAT. A magnetic signature was nearly simultaneously observed at about 0104 UT at the POLAR and Geotail spacecraft. Particle density increases were observed on WIND and Geotail, but not on POLAR. The UV aurora shows an asymmetrical dawn-dusk intensification and presubstorm activity. The significance of these findings will be discussed.

Wuest, M.↗

NASA NTRS1998

Global Auroral Energy Deposition during Substorm Onset Compared with Local Time and Solar Wind IMF Conditions

The global images made by the Ultraviolet Imager (UVI) aboard the IASTP/Polar Satellite are used to derive the global auroral energy deposited in the ionosphere resulting from electron precipitation. During a substorm onset, the energy deposited and its location in local time are compared to the solar wind IMF conditions. Previously, insitu measurements of low orbiting satellites have made precipitating particle measurements along the spacecraft track and global images of the auroral zone, without the ability to quantify energy parameters, have been available. However, usage of the high temporal, spatial, and spectral resolution of consecutive UVI images enables quantitative measurement of the energy deposited in the ionosphere not previously available on a global scale. Data over an extended period beginning in January 1997 will be presented.

Spann, J. F.↗

NASA NTRS1998

Global Observation of Substorm Growth Phase Processes in the Polar Caps

Global images of the polar cap region during the substorm growth phase by the Polar Ultraviolet Imager reveals evidence of the processes which are not completely explained by current models. In particular, it was found that size of the polar cap region increases during the growth phase even if the interplanetary magnetic field has no southward component. Three phenomena were observed to produce an increase in the size of the polar cap: (1) motion of the auroral oval to lower latitude, (2) thinning of the auroral oval, and (3) reduction of intense aurora[ precipitation in the polar region. Correlation of image intensities with in situ particle measurements from the FAST satellite are being conducted to study the three growth phase phenomena; and to help identify the source regions of the particles, the mechanisms involved in producing the auroral structures and what may be reducing the polar cap precipitation during the substorm growth phase.

Brittnacher, M.↗

NASA NTRS1998

A New Synoptic Scale Feature of the Auroral Oval: The Nightside Gap

Th Polar Ultraviolet Imager (UVI) has recently identified a new morphological feature of the nightside aurora in which a well defined segment of the pre-midnight auroral oval, typically spanning 1.0- 1.5 hours in local time (710-1100 km), exhibits a significant reduction in luminosity relative to the active regions surrounding it. This feature appears in roughly 7% of the substorm period observed during our initial study spanning December 1996 through February, 1997. The energy flux (erg/sq cm/s) is shown to be lower by as much as a factor of four in this nightside gaps in comparison to the adjacent auroral activity. Substorm intensifications are often observed on either side of the nightside gap, which remains relatively inactive during these substorm periods. We demonstrate that the nightside gap is sometimes terminated by the onset of a substorm directly within the same local time boundaries. The nightside gap has strong implications for the dynamics of magnetosphere-ionosphere coupling and current closure in the midnight sector auroral oval. Specifically, we conjecture that the nightside gap occurs when transverse ionospheric currents do not feed into upward field-aligned currents in the midnight sector, perhaps due to the Harang discontinuity.

Cliua, D.↗

NASA NTRS1997

Relationship of Topside Ionospheric Ion Outflows to Auroral Forms and Precipitations, Plasma Waves, and Convection Observed by POLAR

The POLAR satellite often observes upflowing ionospheric ions (UFls) in and near the auroral oval on southern perigee (approximately 5000 km altitude) passes. We present the UFI features observed by the thermal ion dynamics experiment (TIDE) and the toroidal imaging mass-angle spectrograph (TIMAS) in the dusk-dawn sector under two different geomagnetic activity conditions in order to elicit their relationships with auroral forms, wave emissions, and convection pattern from additional POLAR instruments. During the active interval, the ultraviolet imager (UVI) observed a bright discrete aurora on the dusk side after the substorm onset and then observed a small isolated aurora form and diffuse auroras on the dawn side during the recovery phase. The UFls showed clear conic distributions when the plasma wave instrument (PWI) detected strong broadband wave emissions below approximately 10 kHz, while no significant auroral activities were observed by UVI. At higher latitudes, the low-energy UFI conics gradually changed to the polar wind component with decreasing intensity of the broadband emissions. V-shaped auroral kilometric radiation (AKR) signatures observed above approximately 200 kHz by PWI coincided with the region where the discrete aurora and the UFI beams were detected. The latitude of these features was lower than that of the UFI conics. During the observations of the UFI beams and conics, the lower-frequency fluctuations observed by the electric field instrument (EFI) were also enhanced, and the convection directions exhibited large fluctuations. It is evident that large electrostatic potential drops produced the precipitating electrons and discrete auroras, the UFI beams, and the AKR, which is also supported by the energetic plasma data from HYDRA. Since the intense broadband emissions were also observed with the UFIs. the ionospheric ions could be energized transversely before or during the parallel acceleration due to the potential drops.

Hirahara, M.↗

NASA NTRS1988

A Study of Space Station Contamination Effects

A workshop was held with the specific objective of reviewing the state-of-knowledge regarding Space Station contamination, the extent to which the various categories of contamination can be predicted, and the extent to which the predicted levels would interfere with onboard scientific investigations or space station functions. The papers presented at the workshop are compiled and address the following topics: natural environment, plasma electromagnetic environment, optical environment, particulate environment, spacecraft contamination, surface physics processes, laboratory experiments and vented chemicals/contaminants.

Torr, M. R.↗