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NASA NTRS1986

Electron-cyclotron maser and solar microwave millisecond spike emission

An intense solar microwave millisecond spike emission (SMMSE) event was observed on May 16, 1981 by Zhao and Jin at Beijing Observatory. The peak flux density of the spikes is high to 5 x 100,000 s.f.u. and the corresponding brightness temperature (BT) reaches approx. 10 to the 15th K. In order to explain the observed properties of SMMSE, it is proposed that a beam of electrons with energy of tens KeV injected from the acceleration region downwards into an emerging magnetic arch forms so-called hollow beam distribution and causes electron-cyclotron maser (ECM) instability. The growth rate of second harmonic X-mode is calculated and its change with time is deduced. It is shown that the saturation time of ECM is t sub s approx. equals 0.42 ms and only at last short stage (delta t less than 0.2 t sub s) the growth rate decreases to zero rather rapidly. So a SMMSE with very high BT will be produced if the ratio of number density of nonthermal electrons to that of background electrons, n sub s/n sub e, is larger than 4 x .00001.

Li, Hong-Wei↗

NASA NTRS1987

Mechanisms for the circular polarization of astrophysical OH masers in star-forming regions and the inferred magnetic fields

Results of further calculations to explore the cause for the circular polarization of astrophysical OH masers in regions of star formation are presented. Calculations are given for both the nonlinear, Zeeman overlap mechanishm, and the Cook mechanism. The previous result that magnetic field strengths of a few milligauss or greater are required, still survives.

Deguchi, Shuji↗

NASA NTRS1986

Observed form and action of the magnetic energy release in flares

The observable spatio-temporal characteristics of the energy release in flares and their association with the magnetic environment and tracers of field dynamics are reviewed. The observations indicate that impulsive phase manifestations, like particle acceleration, may be related to the formation of neutral sheets at the interface between interacting bipoles, but that the site for the bulk of the energy release is within closed loops rather than at the interaction site.

Machado, Marcos E.↗

NASA NTRS1988

An eruptive prominence and associated cm-mm emission outside the solar limb

Radio maps at 22 and 44 GHz are presented which show the emission before and after the eruption of a quiescent prominence located at the west limb. The observed radiation followng the eruption is not consistent with thermal bremsstrahlung mechanism. It can be interpreted as due to gyrosynchrotron emission of nonthermal electrons. The observations appear to be similar to the microwave radiation observed in post-flare loops. This radiation is due to nonthermal electrons trapped in the closed magnetic structures formed after the prominence eruption.

Zodi, A. M.↗

NASA NTRS1989

A theoretical interpretation of upstreaming electrons and elevated conics on auroral field lines

Recent VIKING satellite observations in the auroral zone have shown the association of elevated ion conics (conics with a low energy cutoff above zero) with upward streaming electrons in the presence of low frequency electric field fluctuations. A self-consistent particle simulation was developed which assumed the presence of a steady state electric field on auroral zone field lines capable of accelerating ions up the magnetic field lines. Results from this study show that a low frequency ion-ion two stream instability can be excited. This low frequency instability creates a fluctuating electric field which heats the ions oblique to the magnetic field forming distributions similar to the elevated ion conics. The ion-ion waves also interact resonantly with electrons and accelerates them in the direction of the ion beam.

Ashour-Abdalla, Maha↗

NASA NTRS1990

A study of marine stratocumulus using lidar and other FIRE aircraft observations

The National Center for Atmospheric Research (NCAR) airborne infrared lidar system (NAILS) used in the 1987 First ISCCP Regional Experiment (FIRE) off the coast of California is a 10.6 microns wavelength carbon dioxide lidar system constructed by Ron Schwiesow and co-workers at NCAR. The lidar is particularly well suited for detailed observations of cloud shapes; i.e., height of cloud top (when flying above cloud and looking down) and cloud base (when flying below cloud and looking up) along the flight path. A brief summary of the lidar design characteristics is given. The lidar height resolution of plus or minus 3 m allows for the distance between the aircraft and cloud edge to be determined with this accuracy; however, the duration of the emitted pulse is approximately 3 microseconds, which corresponds to a 500 m pulse length. Therefore, variations in backscatter intensities within the clouds can normally not be resolved. Hence the main parameter obtainable from the lidar is distance to cloud; in some cases the cloud depth can also be determined. During FIRE the lidar was operational on 7 of the 10 Electra flights, and data were taken when the distance between cloud and aircraft (minimum range) was at least 500 m. The lidar was usually operated at 8 Hz, which at a flight speed of 100 m s(-1) translates into a horizontal resolution of about 12 m. The backscatter as function of time (equivalent to distance) for each laser pulse is stored in digital form on magnetic tape. Currently, three independent variables are available to the investigators on the FIRE Electra data tapes: lidar range to cloud, strength of return (relative power), and pulse width of return, which is related to penetration depth.

Jensen, Jorgen B.↗

NASA NTRS1991

Robo-line storage: Low latency, high capacity storage systems over geographically distributed networks

Rapid advances in high performance computing are making possible more complete and accurate computer-based modeling of complex physical phenomena, such as weather front interactions, dynamics of chemical reactions, numerical aerodynamic analysis of airframes, and ocean-land-atmosphere interactions. Many of these 'grand challenge' applications are as demanding of the underlying storage system, in terms of their capacity and bandwidth requirements, as they are on the computational power of the processor. A global view of the Earth's ocean chlorophyll and land vegetation requires over 2 terabytes of raw satellite image data. In this paper, we describe our planned research program in high capacity, high bandwidth storage systems. The project has four overall goals. First, we will examine new methods for high capacity storage systems, made possible by low cost, small form factor magnetic and optical tape systems. Second, access to the storage system will be low latency and high bandwidth. To achieve this, we must interleave data transfer at all levels of the storage system, including devices, controllers, servers, and communications links. Latency will be reduced by extensive caching throughout the storage hierarchy. Third, we will provide effective management of a storage hierarchy, extending the techniques already developed for the Log Structured File System. Finally, we will construct a protototype high capacity file server, suitable for use on the National Research and Education Network (NREN). Such research must be a Cornerstone of any coherent program in high performance computing and communications.

Katz, Randy H.↗

NASA NTRS1992

Low-temperature formation of magnetic iron oxides

Elemental analysis and magnetic measurements of the surface of Mars have indicated the presence of an iron oxide with a considerable magnetic moment. Identification of the oxide phase(s) is an important subject as this may be used to identify the process of weathering on the martian surface as well as the composition of the Mars regolith itself. Consequently, interest was in evidence of new formation of strongly magnetic phases (e.g., magnetite, maghemite, feroxyhyte) in terrestrially derived Mars sample analogs. Within the group of Mars sample analogs derived from low-temperature weathering of basalts in Arctic regions, evidence of magnetic oxides formed at the outermost weathering rind was never observed. However, in one instance where the weathering products accumulating in a crack of a basaltic stone were investigated, evidence of magnetite was found. The experimental details are presented.

Koch, Chr. Bender↗

NASA NTRS1994

The effect of coronal mass ejections on the structure of the heliospheric current sheet

The existence of a stable heliospheric current sheet (HCS) structure near solar cycle maximum was questioned since the recognition that coronal mass ejections (CME's) occur in coronal helmet streamers. Evidence is presented suggesting that pre-existing helmet streamers disrupted or blown out by CME's reform in a time interval much shorter than the life time of the HCS, and that the concept of the HCS has a meaning at any time of thesolar cycle. It appears that the HCS, the current layer that separates adjacent interplanetary magnetic field regions with opposite magnetic polarity, exists throughout the solar cycle, though not always as a thin disk-like sheet. The sheet may be thickened by embedded magnetic ropes formed by CME's, especially near sunspot maximum. The HCS may be used as timing mark in identifying or predicting CME's in the interplanetary medium.

Zhao, Xuepu↗

NASA NTRS1994

Magnetically driven relativistic jets and winds: Exact solutions

We present self-consistent solutions of the full set of ideal MHD equations which describe steady-state relativistic cold outflows from thin accretion disks. The magnetic field forms a spiral which is anchored in the disk, rotates with it, and accelerates the flow out of the disk plane. The collimation at large distances depends on the total amount of electric current that flows along the jet. We considered various distributions of electric current and derived the result that in straight jets which extend to infinite distances, a strong electric current flows along their axis of symmetry. The asymptotic flow velocities are of the order of the initial rotational velocity at the base of the flow (a few tenths of the speed of light). The solutions are applied to both galactic (small-scale) and extragalactic (large-scale) jets.

Contopoulos, J.↗

NASA NTRS1995

Topological structure of the magnetotail as a function of interplanetary magnetic field direction

Magnetic reconnection between the interplanetary magnetic field (IMF) and the geomagnetic field is thought to play a major role in the transfer of solar wind momentum and energy to the magnetosphere. As the angle between the IMF and the geomagnetic field is changed at the bow of the magnetosphere, the topological record of the location of the reconnection region should be recorded in the magnetosheath and on the magnetopause along the flanks of the tail, because the super fast flow freezes strong magnetic gradients formed in the bow reconnection regions into the plasma downstream. In this report, we present results from a three-dimensional, magnetohydrodynamic (MHD), global numerical simulation code for the location of the separatrix between unconnected IMF magnetosheath field lines and reconnected field lines which penetrate the magnetopause and connect to the polar ionosphere. The angle between the IMF direction and the line where the separatrix crosses the magnetopause is shown to be a sensitive function of the IMF clock angle. We also explain how this behavior can be used to derive an approximate relation for the dependence of the cross-polar voltage on the IMF clock angle. We conclude with a note of caution concerning the importance of physical boundary conditions in magnetoplasma simulations.

Fedder, J. A.↗

NASA NTRS1995

The double oval UV auroral distribution. 2: The most poleward arc system and the dynamics of the magnetotail

The poleward arc system of a double oval distribution is shown to activate at the end of the optical expansion phase signifying the beginning of substorm recovery. The velocity dispersed ion signature (VDIS) can exist coincident with this discrete aurora developing on the most poleward oval. Although the VDIS is usually associated with ion beams in the plasma sheet boundary layer, it is demonstrated that the ionospheric signature is not beamlike but distributed in pitch angle. At the time when the double oval begins to form, the magnetic field in the magnetotail lobe becomes less flared and can show Pc 5 period oscillations. Similar pulsations also exist in the ionosphere associated with the most poleward oval and with stationary surge formation. Theoretical considerations link this phenomenon with a wave source tailward of x(sub GSE) = -30R(sub E) and fast mode evanescent waves propagating earthward in the tail lobe region. In this case the magnetotail appears to act like a waveguide and the plasma sheet boundary layer as a resonance region. This implies that the coupling of this fast mode waves is with the plasma sheet boundary layer and not with dipolar like field lines. The implications of this for the reconnection model of substorms are discussed.

Elphinstone, R. D.↗

NASA NTRS1995

Hybrid superconductor magnet bearings

Hybrid superconductor magnet bearings (HSMB's) utilize high temperature superconductors (HTS's) together with permanent magnets to form a frictionless interface between relatively rotating parts. They are low mass, stable, and do not incur expenditure of energy during normal operation. There is no direct physical contact between rotor and stator, and hence there is no wear and tear. However, just as any other applications of HTS's, it requires a very cold temperature to function. Whereas this might be perceived as a disadvantage on earth, it is of no great concern in space or on the moon. To astronomers, the moon is an excellent site for an observatory, but the cold and dusty vacuum environment on the moon precludes the use of mechanical bearings on the telescope mounts. Furthermore, drive mechanisms with very fine steps, and hence bearings with extremely low friction are needed to track a star from the moon, because the moon rotates very slowly. All aspects considered, the HSMB is about the only candidate that fits in naturally. Here, we present a design for one such bearing, capable of supporting a telescope that weighs about 3 lbs on Earth.

Chu, Wei-Kan↗

NASA NTRS2005

The Solar Ultraviolet Magnetograph Investigation: Polarization Properties

This paper will describe the objectives of the Marshall Space Flight Center (MSFC) Solar Ultraviolet Magnetograph Investigation (SUMI) and the optical components that have been developed to meet those objectives. A sounding rocket payload is being developed to test the feasibility of magnetic field measurements in the Sun s transition region. This paper will review the scientific measurements that will be made by the SUMI sounding rocket program, and the optics have been optimized for simultaneous measurements of two magnetic lines formed in the transition region (CIV at 1550 A and MgII at 2800 A). Finally, this paper will concentrate on the polarization properties of the SUM1 polarimeter and toroidal varied-line-space gratings.

West, E. A.↗

NASA NTRS1977

Bubble domain circuit organization

An on-chip bubble domain circuit organization. One or more storage registers are connected to a propagation path whereby data in the form of magnetic bubble domains (bubbles) may be transferred into and out of the storage registers. The propagation path includes a generator for producing the initial bubbles which are expanded into any desired number of new bubbles by a unique multiple output replicator. A unique input decoder is utilized to determine to which storage register the bubbles from the replicator will be directed along the propagation path. Those bubbles not selected may be annihilated. An output decoder utilizing essentially the same decoding scheme as the input decoder, selectively receives bubbles from the storage register. A transfer and replicate switch is utilized between the storage register and output decoder to selectively transfer bubbles to the output decoder. The output decoder may collapse all of the bubbles from certain storage registers so that only the information from the selected storage register reaches the detector. The detectors in turn produce the chip output signal. External control electronics are utilized to control the selective operation of the various devices utilized in the propagation path.

Chen, Thomas T.↗

NASA NTRS2010

Heliophysics 2009 Roadmap and Global Change: Possibilities for Improved Understanding of the Connection

Heliophysics is the science that includes all aspects of the research needed to understand the Sun and its effects on the Earth and the solar system. Six science targets: 1. Origins of Near-Earth Plasma - to understand the origin and transport of terrestrial plasma from its source to the magnetosphere and solar wind. 2. Solar Energetic Particle Acceleration and Transport - to understand how and where solar eruptions accelerate energetic particles that reach Earth. 3. Ion-Neutral Coupling in the Atmosphere - to understand how neutral winds control ionospheric variability. 4. Climate Impacts of Space Radiation - to understand our atmosphere s response to auroral, radiation belt, and solar energetic particles, and the associated effects on nitric oxide (NO) and ozone. 5. Dynamic Geospace Coupling - to understand how magnetospheric dynamics provides energy into the coupled ionosphere-magnetosphere system. 6. Heliospheric Magnetics - to understand the flow and dynamics of transient magnetic structures form the solar interior to Earth.

Spann, Jim↗

NASA NTRS2010

CME Initiation and Reconnection

Coronal mass ejections (CMEs) are the most massive explosions in the heliosphere, and the primary drivers of geoeffective space weather. This talk will be focused on fast CMEs, which travel at Alfvenic speeds as high as 2500 km/s. These ejections are associated with solar flares, prominence eruptions, and energetic particles accelerated near the Sun and in interplanetary space. CMEs require sufficient energy storage, in the form of magnetic stress, and rapid release of this energy. Although it is generally agreed that magnetic reconnection is the key to fast CME initiation, different models incorporate reconnection in different ways. One promising model --- the breakout scenario --- involves reconnection in two distinct yet interconnected locations: breakout reconnection ahead of the CME, and flare reconnect ion behind it. This model has been validated through 2D and 3D MHD simulations and favorable comparison with the observed properties of many fast CMEs. I will discuss what we have learned about the onset and evolution of breakout and flare reconnect ion from recent high-resolution 2D simulations of CME initiation with adaptive mesh refinement and numerical resistivity.

Karpen, Judy T.↗

NASA NTRS2012

Solar Eruptions: Coronal Mass Ejections and Flares

This lecture introduces the topic of Coronal mass ejections (CMEs) and solar flares, collectively known as solar eruptions. During solar eruptions, the released energy flows out from the Sun in the form of magnetized plasma and electromagnetic radiation. The electromagnetic radiation suddenly increases the ionization content of the ionosphere, thus impacting communication and navigation systems. Flares can be eruptive or confined. Eruptive flares accompany CMEs, while confined flares hav~ only electromagnetic signature. CMEs can drive MHD shocks that accelerate charged particles to very high energies in the interplanetary space, which pose radiation hazard to astronauts and space systems. CMEs heading in the direction of Earth arrive in about two days and impact Earth's magnetosphere, producing geomagnetic storms. The magnetic storms result in a number of effects including induced curr~nts that can disrupt power grids, railroads, and underground pipelines

Gopalswamy, Nat↗