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Description: BS>The theories of the origin of the aurora are discussed from two points of view. The two basic structural types of auroras are described. A discussion is included of radio whistlers. (W.L.H.)
Date: April 1, 1959
Creator: Chamberlain, J.W.
Partner: UNT Libraries Government Documents Department

New perspectives on substorm injections

Description: There has been significant progress in understanding substorm injections since the Third International Conference on Substorms in 1996. Progress has come from a combination of new theories, quantitative modeling, and observations--particularly multi-satellite observations. There is now mounting evidence that fast convective flows are the mechanism that directly couples substorm processes in the mid tail, where reconnection occurs, with substorm processes the inner magnetosphere where Pi2 pulsations, auroral breakups, and substorm injections occur. This paper presents evidence that those flows combined with an earthward-propagating compressional wave are responsible for substorm injections and discusses how that model can account for various substorm injection signatures.
Date: December 1, 1998
Creator: Reeves, G.D.
Partner: UNT Libraries Government Documents Department

Experimental studies of auroral arc generators

Description: This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). An all-sky video camera system was deployed in Eagle, Alaska at the foot of the magnetic field line that threads geosynchronous satellite 1989-046 as part of a campaign to study correlations of ground-based auroral activity with satellite-based plasma and energetic particle measurements. The overall intent of the project was to study magnetosphere-ionosphere coupling as it relates to the aurora, and, in particular, to look for signatures that may help to identify various auroral generator mechanism(s). During this study, our efforts were primarily directed towards identifying the generator mechanism(s) for pulsating aurora. Our data, though not conclusive, are found to support theories that propose a cyclotron resonance mechanism for the generation of auroral pulsations.
Date: August 1, 1997
Creator: Suszcynsky, D.M.; Borovsky, J.E. & Thomsen, M.F.
Partner: UNT Libraries Government Documents Department

Stable auroral red arcs

Description: Sar-arcs are diffuse, persistent, practically monochromatic ( lambda lambda 6300 to 64A) auroral forms peculiar to mid-latitude regions of Earth. Measurements of such parameters as spectral composition, geomagnetic location, range of intensity, and frequency of occurrence lead to the conclusion that the phenomenon is due to the excitation of atomic oxygen by hot electrons in the plasmapause region. However, on the basis of the the data available, it is not clear whether fresh electrons are precipitating into the region of the arc or whether ambient electrons are being heated in place. There is strong evidence that the source of energy in either case is the ring current. Suggested mechanisms by which energy is transferred from the ring current to the electrons in the SAR-arc region are: 1) heat flow, that is, transfer of kinetic energy to the SAR-arc region by Coulomb collisions, 2) transfer of ring current proton kinetic energy to hydromagnetic waves which are in turn damped by the electrons in the SAR-arc region, 3) direct influx of energetic electrons into the SAR-arc region. Which of these mechanisms predominates is still not resolved at this time. There are other open questions as well including ones dealing with the motion of the arcs and the spectral composition. (auth)
Date: January 1, 1973
Creator: Hoch, R.J.
Partner: UNT Libraries Government Documents Department

Measuring the magnetic connectivity of the geosynchronous region of the magnetosphere

Description: This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The purpose of this project was to determine the magnetic connectivity of the geosynchronous region of the magnetosphere to the auroral zone in the polar ionosphere in order to test and refine current magnetospheric magnetic field models. The authors used plasma data from LANL instruments on three geosynchronous satellites and from USAF instruments on three low-altitude, polar-orbiting, DMSP satellites. Magnetic connectivity is tested by comparing plasma energy spectra at DMSP and geosynchronous satellites when they are in near conjunction. The times of closest conjugacy are used to evaluate the field models. They developed the tools for each step of the process and applied them to the study of a one-week test set of conjunctions. They automated the analysis tools and applied them to four months of two-satellite observations. This produced a database of about 130 definitive magnetic conjunctions. They compared this database with the predictions of the widely-used Tsyganenko magnetic field model and showed that in most cases one of the various parameterizations of the model could reproduce the observed field line connection. Further, they explored various measurables (e.g., magnetospheric activity indices or the geosynchronous field orientation) that might point to the appropriate parameterization of the model for these conjunctions, and ultimately, for arbitrary times.
Date: March 1, 1996
Creator: Thomsen, M.; Hones, E.; McComas, D.; Reeves, G. & Weiss, L.
Partner: UNT Libraries Government Documents Department


Description: It is suggested that corpuscular radiation is hydrodynamic expansion of the solar corona which is called solar wind. Arguments are presented for this expansion of the solar corona in terms of motion of the comet tail aurorae production, magnetic storms, and cosmic-ray effects on earth. The corona is taken to be isotherrnal out to an undefined distance (in multiples of the radius of the base of the corona) and from there it expands adiabatically until supersonic velocities are reached at infinity. The solar wind is considered to continue after five astronomical units on the spiralling solar magnetic field. Applications of the solar wind hypothesis to solar sailing are discussed. (C.J.G.)
Date: November 1, 1959
Creator: Parker, E.N.
Partner: UNT Libraries Government Documents Department

Association of an auroral surge with plasma sheet recovery and the retreat of the substorm neutral line

Description: One of the periods being studied in the PROMIS CDAW (CDAW-9) workshops is the interval 0000-1200 UT on May 3, 1986, designated Event 9C.'' A well-defined substorm, starting at 0919 UT, was imaged by both DE 1 over the southern hemisphere and Viking over the northern hemisphere. The images from Viking, at 80-second time resolution, showed a surge-like feature forming at about 0952 UT at the poleward edge of the late evening sector of the oval. The feature remained relatively stationary until about 1000 UT when it seemed to start advancing westward. ISEE 1 and 2 were closely conjugate to the surge as mapped from both the DMSP and Viking images. We conclude that the plasma sheet recovery was occasioned by the arrival at ISEE 1,2 of a westward traveling wave of plasma sheet thickening, the wave itself being formed by westward progression of the substorm neutral line's tailward retreat. The westward traveling surge was the auroral manifestation of this nonuniform retreat of the neutral line. We suggest that the upward field aligned current measured by DMSP F7 above the surge head was driven by plasma velocity shear in the plasma sheet at the duskward kink'' in the retreating neutral line. By analogy with this observation we propose that the westward traveling surges and the current wedge field aligned currents that characterize the expanding auroral bulge during substorm expansive phase are manifestations of (and are driven by) velocity shear in the plasma sheet near the ends of the extending substorm neutral line.
Date: January 1, 1990
Creator: Hones, E.W. (Mission Research Corp., Los Alamos, NM (USA)); Elphinstone, R.; Murphree, J.S. (Calgary Univ., AB (Canada). Dept. of Physics); Galvin, A.B. (Maryland Univ., College Park, MD (USA). Dept. of Space Physics); Heinemann, N.C. (Boston Coll., Chestnut Hill, MA (USA). Dept. of Physics); Parks, G.K. (Washington Univ., Seattle, WA (USA)) et al.
Partner: UNT Libraries Government Documents Department

Poleward leaping auroras, the substorm expansive and recovery phases and the recovery of the plasma sheet

Description: The auroral motions and geomagnetic changes the characterize the substorm's expansive phase, maximum epoch, and recovery phase are discussed in the context of their possible associations with the dropout and, especially, the recovery of the magnetotail plasma sheet. The evidence that there may be an inordinately sudden large poleward excursion or displacement (a poleward leap) of the electrojet and the auroras at the expansive phase-recovery phase transition is described. The close temporal association of these signatures with the recovery of the plasma sheet, observed on many occasions, suggests a causal relationship between substorm maximum epoch and recovery phase on the one hand and plasma sheet recovery on the other.
Date: January 1, 1992
Creator: Hones, E.W.
Partner: UNT Libraries Government Documents Department

Study of a substorm on May 4, 1986

Description: A substorm on May 4, 1986, midway through the PROMIS campaign of coordinated data acquisition, was uniquely well documented. Both in its aspects at earth and in its magnetotail aspects. The expansive phase onset was imaged by the Viking satellite at 20-second time resolution. Most of the expansive phase was also imaged by DE 1 at 6-minute time resolution. ISEE 1 and 2 were near the tail's axis 18.5 R/sub e/ from earth operating at high data rate and data were recorded by several geosynchronous satellites. This multi-satellite study provides evidence that the active substorm aurora occurs at the feet of field lines that map to a magnetic X-line in the near tail. The longitudinal extension of the aurora during a substorm is associated with cross-rail lengthening of the near-earth neutral line. The concept of the ''poleward leap'' of the auroral electrojet (and the auroras) as the culminating feature of the expansive phase finds further support in these data. 7 refs., 6 figs.
Date: January 1, 1988
Creator: Hones, E.W.; Craven, J.D.; Frank, L.A.; Galvin, A.B.; Murphree, J.S.; Elphinstone, R.D. et al.
Partner: UNT Libraries Government Documents Department

Stable Auroral Red arc occurrences detected by the Pacific Northwest Laboratory photometer network: A decade of observations, 1978--1988

Description: Using data obtained from a network of all-sky scanning photometers designed to operate routinely for long periods of time, a comprehensive inspection of observations covering the time period 1978--1988 has revealed features that we interpret to be Stable Auroral Red (SAR) arcs during 250 nighttime observing periods. These arcs result from high temperature within the ionospheric electron gas that is maintained by slow leakage of energy from the earth's magnetosphere. A listing of these events, the most complete available for this time interval, is presented for the purpose of complementing observations reported for earlier dates. This listing is composed of location of the observing photometer, date, time, photometric intensity, and location (as defined by the earth's magnetic coordinate system). The intent is to make these observations available to a broad range of researchers and thereby initiate further investigations of these features. 22 refs., 3 figs., 2 tabs.
Date: November 1, 1989
Creator: Slater, D.W. & Kleckner, E.W.
Partner: UNT Libraries Government Documents Department

Evaluation of some geophysical events on 22 September 1979

Description: TIROS-N plasma data and related geophysical data measured on 22 September 1979 were analyzed to determine whether the electron precipitation event detected by TIROS-N at 00:54:49 universal time could have been related to a surface nuclear burst (SNB). The occurrence of such a burst was inferred from light signals detected by two Vela bhangmeters approx. 2 min before the TIROS-N event. The precipitation was found to be unusually large but not unique. It probably resulted from passage of TIROS-N through The precipitating electrons above a pre-existing auroral arc that may have brightened to an unusually high intensity from natural causes approx. 3 min before the Vela signals. On the othe hand, no data were found that were inconsistent with the SNB interpretation of the 22 September Vela observations. In fact, a patch of auroral light that suddenly appeared in the sky near Syowa Base, Antarctica a few seconds after the Vela event can be interpreted (though not uniquely) as a consequence of the electromagnetic pulse of an SNB.
Date: April 1, 1981
Creator: Hones, E.W. Jr.; Baker, D.N. & Feldman, W.C.
Partner: UNT Libraries Government Documents Department

Coordinated ground-based and geosynchronous satellite-based measurements of auroral pulsations

Description: We describe a technique that uses a ground-based all-sky video camera and geosynchronous satellite-based plasma and energetic particle detectors to study ionosphere-magnetosphere coupling as it relates to the aurora. The video camera system was deployed in Eagle, Alaska for a seven month period at the foot of the magnetic field line that threads geosynchronous satellite 1989-046. Since 1989-046 corotates with the earth, its footprint remains nearly fixed in the vicinity of Eagle, allowing for routine continuous monitoring of an auroral field line at its intersections with the ground and with geosynchronous orbit. As an example of the utility of this technique, we present coordinated ground-based and satellite based observations during periods of auroral pulsations and compare this data to the predictions of both the relaxation oscillator theory and flow cyclotron maser theory for the generation of pulsating aurorae. The observed plasma and energetic particle characteristics at geosynchronous orbit during pulsating aurorae displays are found to be in agreement with the predictions of both theories lending further support that a cyclotron resonance mechanism is responsible for auroral pulsations.
Date: September 1, 1996
Creator: Suszcynsky, David M.; Borovsky, Joseph E.; Thomsen, Michelle F.; McComas, David J. & Belian, Richard D.
Partner: UNT Libraries Government Documents Department

Impulsive ion acceleration in earth's outer magnetosphere

Description: Considerable observational evidence is found that ions are accelerated to high energies in the outer magnetosphere during geomagnetic disturbances. The acceleration often appears to be quite impulsive causing temporally brief (10's of seconds), very intense bursts of ions in the distant plasma sheet as well as in the near-tail region. These ion bursts extend in energy from 10's of keV to over 1 MeV and are closely associated with substorm expansive phase onsets. Although the very energetic ions are not of dominant importance for magnetotail plasma dynamics, they serve as an important tracer population. Their absolute intensity and brief temporal appearance bespeaks a strong and rapid acceleration process in the near-tail, very probably involving large induced electric fields substantially greater than those associated with cross-tail potential drops. Subsequent to their impulsive acceleration, these ions are injected into the outer trapping regions forming ion ''drift echo'' events, as well as streaming tailward away from their acceleration site in the near-earth plasma sheet. Most auroral ion acceleration processes occur (or are greatly enhanced) during the time that these global magnetospheric events are occurring in the magnetotail. A qualitative model relating energetic ion populations to near-tail magnetic reconnection at substorm onset followed by global redistribution is quite successful in explaining the primary observational features. Recent measurements of the elemental composition and charge-states have proven valuable for showing the source (solar wind or ionosphere) of the original plasma population from which the ions were accelerated.
Date: January 1, 1985
Creator: Baker, D.N. & Belian, R.D.
Partner: UNT Libraries Government Documents Department

Heating of heavy ions on auroral field lines

Description: Heating of heavy ions is studied in the presence of large amplitude hydrogen cyclotron waves. A three wave decay process, in which a large amplitude pump hydrogen cyclotron wave decays into a daughter hydrogen cyclotron wave and a low frequency oxygen cyclotron wave, is studied theoretically and by numerical simulations. The numerical simulations show a decay instability resulting in strong heating of both the oxygen ions and the hydrogen ions. In particular, the high energy tail of the oxygen ions is observed in the perpendicular distribution.
Date: January 1, 1983
Creator: Nishikawa, K.I. & Okuda, H., Hasegawa, A.
Partner: UNT Libraries Government Documents Department

Acceleration of hydrogen ions and conic formation along auroral field lines

Description: Electrostatic ion cyclotron turbulence and the formation of ion conics at low altitudes (approx. = 1500 km) along auroral field lines have been investigated analytically and by plasma numerical simulations. Ion cyclotron waves are assumed to be driven unstable by the up-going cold ionospheric electrons associated with the downward auroral current. When the electron drift speed is comparable to the electron thermal speed, it is found that the large amplitude, e phi/T/sub e/ approx. = 1, coherent, ..omega.. = ..cap omega../sub i/, ion cyclotron waves shoudl exist along auroral field lines at low altitudes extending approx. = 500 to 1000 km. Ion conics are associated with the cyclotron turbulence and the ion bulk temperature is found to increase a factor of 10 of the initial ionospheric temperature, while the temperature of the high energy tail can be as much as a factor of 100 of the ionospheric temperature. Theory and simulations agree well.
Date: May 1, 1982
Creator: Okuda, H. & Ashour-Abdalla, M.
Partner: UNT Libraries Government Documents Department


Description: Discussion of theories on particle motion in electric and magnetic fields precedes examination of theories on the source of the inner and outer Van Allen belts. Theories for the inner belt propose solar cosmic ray injection and galactic cosmic ray injection as the source of the protons. Neutron albedo is particularly examined but seems to be unaccountable for the proton belt. Neutron albedo and injection from the sun are also considered as possible sources of the electrons in the outer belt. Fluctuations, intensities, and distributions of the belts are also discussed, and the connection between the belts and aurora displays is examined. Fluxes, spectra, and particle intensities are displayed, and the effects of magnetic storms on the belts are analyzed. 150 references. (D.C.W.)
Date: February 15, 1963
Creator: Kistler, V. E.
Partner: UNT Libraries Government Documents Department

Quasilinear simulation of auroral kilometric radiation by a relativistic Fokker-Planck code

Description: An intense terrestrial radiation called the auroral kilometric radiation (AKR) is believed to be generated by cyclotron maser instability. We study a quasilinear evolution of this instability by means of a two-dimensional relativistic Fokker-Planck code which treats waves and distributions self-consistently, including radiation loss and electron source and sink. We compare the distributions and wave amplitude with spacecraft observations to elucidate physical processes involved. 3 refs., 1 fig.
Date: January 1, 1991
Creator: Matsuda, Y.
Partner: UNT Libraries Government Documents Department

Plasma sheet behavior during substorms

Description: Auroral or magnetic substorms are periods of enhanced auroral and geomagnetic activity lasting one to a few hours that signify increased dissipation of energy from the magnetosphere to the earth. Data acquired during the past decade from satellites in the near-earth sector of the magnetotail have suggested that during a substorm part of the plasma sheet is severed from earth by magnetic reconnection, forming a plasmoid, i.e., a body of plasma and closed magnetic loops, that flows out of the tail into the solar wind, thus returning plasma and energy that have earlier been accumulated from the solar wind. Very recently this picture has been dramatically confirmed by observations, with the ISEE 3 spacecraft in the magnetotail 220 R/sub E/ from earth, of plasmoids passing that location in clear delayed response to substorms. It now appears that plasmoid release is a fundamental process whereby the magnetosphere gives up excess stored energy and plasma, much like comets are seen to do, and that the phenomena of the substorm seen at earth are a by-product of that fundamental process.
Date: January 1, 1983
Creator: Hones, E.W. Jr.
Partner: UNT Libraries Government Documents Department