ORIGIN OF BLACK SPHERULES FROM PACIFIC ISLANDS, DEEP SEA SEDIMENTS AND ANTARCTIC ICE
Origin of black spherules from pacific islands, deep sea sediments and antarctic ice
ANTARCTICA↗
SEARCH · Search NASA
Results for “magnetic islands”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Substorms At Jupiter: Galileo Observations of Transient Reconnection in The Near Tail
The magnetic flux content of the Jovian magnetosphere is set by the internal dynamo, but those magnetic field lines are constantly being loaded by heavy ions at the orbit of lo and dragged inexorably outward by the centrifugal force. Vasyliunas has proposed a steady state reconnecting magnetospheric model that sheds plasma islands of zero net magnetic flux and returns nearly empty flux tubes to the inner magnetosphere. The Galileo observations indicate that beyond 40 Rj the current sheet begins to tear and beyond 50 Rj on the nightside explosively reconnects as the tearing site reaches the low density lobe region above and below the current sheet. Small events occur irregularly but on average about every 4 hours and large events about once a day. The magnetic flux reconnected in such events amounts up to about 70,000 Webers/sec and is sufficient to return the outwardly convected magnetic flux to the inner magnetosphere. Since this process releases plasmoids into the jovian tail, as do terrestrial substorms; since this process involves explosive reconnection across the current sheet on the nightside of the planet, as do terrestrial substorms; and since the process is a key in closing the circulation pattern of the magnetic and plasma flux, as it is in terrestrial substorms; we refer to these events as jovian substorms.
Russell, C. T.↗
Multiple Spacecraft Study of the Impact of Turbulence on Reconnection Rates
Magnetic turbulence and secondary island formation have reemerged as possible explanations for fast reconnection. Recent three-dimensional simulations reveal the formation of secondary islands that serve to shorten the current sheet and increase the accelerating electric field, while both simulations and observations witness electron holes whose collapse energizes electrons. However, few data studies have explicitly investigated the effect of turbulence and islands on the reconnection rate. We present a more comprehensive analysis of the effect of turbulence and islands on reconnection rates observed in space. Our approach takes advantage of multiple spacecraft to find the location of the spacecraft relative to the inflow and the outflow, to estimate the reconnection electric field, to indicate the presence and size of islands, and to determine wave vectors indicating turbulence. A superposed epoch analysis provides independent estimates of spatial scales and a reconnection electric field. We apply k-filtering and a new method adopted from seismological analyses to identify the wavevectors. From several case studies of reconnection events, we obtain preliminary estimates of the spectral scaling law, identify wave modes, and present a method for finding the reconnection electric field associated with the wave modes.
Wendel, Deirdre↗
An Assessment of Magnetic Conditions for Strong Coronal Heating in Solar Active Regions by Comparing Observed Loops with Computed Potential Field Lines
We report further results on the magnetic origins of coronal heating found from registering coronal images with photospheric vector magnetograms. For two complementary active regions, we use computed potential field lines to examine the global non-potentiality of bright extended coronal loops and the three-dimensional structure of the magnetic field at their feet, and assess the role of these magnetic conditions in the strong coronal heating in these loops. The two active regions are complementary, in that one is globally potential and the other is globally nonpotential, while each is predominantly bipolar, and each has an island of included polarity in its trailing polarity domain. We find the following: (1) The brightest main-arch loops of the globally potential active region are brighter than the brightest main- arch loops of the globally strongly nonpotential active region. (2) In each active region, only a few of the mainarch magnetic loops are strongly heated, and these are all rooted near the island. (3) The end of each main-arch bright loop apparently bifurcates above the island, so that it embraces the island and the magnetic null above the island. (4) At any one time, there are other main-arch magnetic loops that embrace the island in the same manner as do the bright loops but that are not selected for strong coronal heating. (5) There is continual microflaring in sheared core fields around the island, but the main-arch bright loops show little response to these microflares. From these observational and modeling results we draw the following conclusions: (1) The heating of the main-arch bright loops arises mainly from conditions at the island end of these loops and not from their global non-potentiality. (2) There is, at most, only a loose coupling between the coronal heating in the bright loops of the main arch and the coronal heating in the sheared core fields at their feet, although in both the heating is driven by conditions/events in and around the island. (3) The main-arch bright loops are likely to be heated via reconnection driven at the magnetic null over the island. The details of how and where (along the null line) the reconnection is driven determine which of the split-end loops are selected for strong heating. (4) The null does not appear to be directly involved in the heating of the sheared core fields or in the heating of an extended loop rooted in the island. Rather, these all appear to be heated by microflares in the sheared core field.
Gary, G. A.↗
Investigation from Japanese MAGSAT Team. Part A. Crustal structure near Japan and in Antarctic station. Part B. Electric currents and hydromagnetic waves in the ionosphere and the magnetosphere
Preliminary results of MAGSAT data analysis are described. Regional anomaly maps (deviations from the MGST model field) for X,Y,Z, and F in the area of 115 to 155 deg E and 20 to 60 deg N were obtained. A similar map for the geomagnetic total force anomaly in the vicinity of Japan showed that the observed anomaly can be explained by the difference in crustal magnetization between the Japan Sea and the Japan Island, which reflects a difference of 25 km in the thickness of the magnetized layer. The MAGSAT record of a sudden commencement of a magnetic storm above the South Atlantic Ocean showed a reverse impulse particularly in the D-component. Results relating to toroidal currents in the ionosphere, transverse and parallel perturbations over the polar regions, the relationship between field aligned currents and precipitating electrons, and the calculation of the subsatellite electric field are also discussed.
Fukushima, N.↗
ISEE-1 and 2 observations of magnetic flux ropes in the magnetotail - FTE's in the plasma sheet?
Magnetic field observations on ISEE-1 and 2 in and near the neutral sheet about 20 Re down the near-earth magnetotail reveal the occurrence of structures resembling magnetic flux ropes. Both electric field and fast plasma data show that these structures convect across the spacecraft at speeds of 200 - 600 km/s, and that they have scale sizes of roughly 3 5 Re. The rope axis orientation is across the tail, approximately in the -Y GSM direction. Their magnetic structure is strikingly similar to magnetic flux ropes observed in the Venus ionosphere, and to flux transfer events observed at the dayside magnetopause. The total field-aligned current within these ropes may approach a million amps. These structures may arise because of patchy reconnection within the plasma sheet, or may be tearing islands formed when the plasma sheet magnetic field has a cross-tail component. Plasma sheet flux ropes are not a common feature at ISEE orbital altitudes; this suggests that near-earth neutral line formation within ISEE apogee (22 Re) may be equally rare.
Elphic, R. C.↗
Airborne Geomagnetic Investigations at the Haughton Impact Structure, Devon Island, Nunavut, Canada
This investigation created a broad magnetic map of the 23 Ma Haughton impact structure, in order to characterize its geomagnetic signature. Additional information is contained in the original extended abstract.
Glass, B. J.↗
Observations of Closed Structures at the Magnetopause: A Case for Multiple Reconnections
We further analyze a case of Interball LLBL crossing on the dusk flank of geomagnetosphere under southward magnetosheath magnetic field, previously categorized as an interval of highly structured LLBL. These conditions of highly structured LLBL include reconnection signatures. Observed ion velocity distributions with LLBL are quite variable. D-shaped distributions that are associated with the open reconnected flux tube are observed at the boundaries of LLBL transients and sometimes within the LLBL transients. In most cases the ion velocity distributions consist of two magnetosheath-type components with different velocities parallel to the magnetic field, or of three components one of which has nearly zero Vpar. The shapes of ion velocity distributions and their evolution with decreasing number density in LLBL indicate that most of LLBL is located on closed magnetic field lines. These observations strongly favor multiple reconnections between magnetosheath and magnetosphereric flux tubes, creating long spiral flux tube islands at the magnetopause. We report evidence for the simultaneous occurrence of magnetic reconnection at multiple points across the magnetopause, as has been proposed and found to occur in magnetopause simulations. The evidence is in the form of highly structured distributions of ions in velocity parallel to the local magnetic field direction, within the magnetopause and low latitude boundary layer region, from the Interball-Tall spacecraft. We interpret these distributions as a natural consequence of the formation of spiral magnetic flux tubes consisting of a mixture of alternating segments originating from the magnetosheath or interplanetary plasma and from the low latitude boundary layer or magnetospheric plasma. We further analyze a case of Interball LLBL crossing on the dusk flank of geomagnetosphere under southward magnetosheath magnetic field, previously categorized as an interval of highly structured LLBL. These conditions of highly structured LLBL include reconnection signatures. Observed ion velocity distributions with LLBL are quite variable. D-shaped distributions that are associated with the open reconnected flux tube are observed at the boundaries of LLBL transients and sometimes within the LLBL transients. In most cases the ion velocity distributions consist of two magnetosheath-type components with different velocities parallel to the magnetic field, or of three components one of which has nearly zero Vpar. The shapes of ion velocity distributions and their evolution with decreasing number density in LLBL indicate that most of LLBL is located on closed magnetic field lines. These observations strongly favor multiple reconnection between magnetosheath and magnetospheric flux tubes, creating long spiral flux tube islands at the magnetopause. We report evidence for the simultaneous occurrence of magnetic reconnection at multiple points across the magnetopause, as has been proposed and found to occur in magnetopause simulations. The evidence is in the form of highly structured distributions of ions in velocity parallel to the local magnetic field direction, within the magnetopause and low latitude boundary layer region, from the Interball-Tail spacecraft. We interpret these distributions as a natural consequence of the formation of spiral. We further analyze a case of Interball LLBL crossing on the dusk flank of geomagnetosphere under southward magnetosheath magnetic field, previously categorized as an interval of highly structured LLBL. These conditions of highly structured LLBL include reconnection signatures. Observed ion velocity distributions with LLBL are quite variable. D-shaped distributions that are associated with the open reconnected flux tube are observed at the boundaries of LLBL transients and sometimes within the LLBL transients. In most cases the ion velocity distributions consist of two magnetosheath-type components with different velocities parallel to the magnetic field, or of three components one of which has nearly zero Vpar.
Vaisberg, O. L.↗
Wide and Narrow CMEs and Their Source Explosions Observed at the Spring 2003 SOHO-Sun-Ulysses Quadrature
At the time of the spring 2003 Ulysses-SOHO-Sun quadrature, Ulysses was off the East limb of the Sun at 14.5 degrees north latitude and 4.91 AU. LASCO/C2 images show small transient events that originated from near the limb on May 25, 26 and 27 in the north-east quadrant, along with a large Coronal Mass Ejection (CME) that originated from an active region near disk center on May 26. Ulysses data bear clear signatures of the large CME, specifically including an enhanced abundance of highly ionized Fe. SOHO/UVCS spectra at 1.75 solar radii, near the radial direction to Ulysses, give no evidence of emission from high temperature lines, even for the large CME: instead, for the small events, occasional transient high emission in cool lines was observed, such as the CIII 977 Angstrom line usually absent at coronal levels. Each of these events lasted ca. 1 hour or less and never affected lines from ions forming above ca. 106K. Compact eruptions in Helium 304 Angstrom EIT images, related to the small UVCS transients, were observed at the limb of the Sun over the same period. At least one of these surge events produced a narrow CME observed in LASCO/C2. Most probably all these events are compact magnetic explosions (surges/jets, from around a small island of included polarity) which ejected cool material from lower levels. Ulysses data have been analyzed to find evidence of the cool, narrow CME events, but none or little was found. This puzzling scenario, where events seen by UVCS have no in situ counterparts and vice versa, can be partially explained once the region where the large CME originated is recognized as being at the center of the solar disk so that the CME material was actually much further from the Sun than the 1.7 Rsun height of the UVCS slit off the limb. Conversely, the narrow events may simply have missed Ulysses or been too brief for reliable signatures in composition and ionization state. A basic feature demonstrated by these observations is that large magnetic explosions produce wide-angle CMEs whereas compact magnetic explosions produce narrow CMEs. The results show that quadrature observations need some luck to be successfull: that is, events must be in the plane of the sky to allow SOHO/UVCS and Ulysses to sample the same plasma. This will most easily occur in winter 2007 and winter 2008, when the quadrature geometry will allow for prolonged observations.
Suess, Steven↗
Ion Velocity Distributions Within LLBL and Their Possible Implication to Multiple Reconnections
We analyze two LLBL crossings made by Interball Tail satellite under southward or variable magnetosheath magnetic field: one crossing on the flank of the magnetosphere, and another one closer to the subsolar point. Three different types of ion velocity distributions within LLBL are observed: (a) D-shaped distributions, (b) ion velocity distributions consisting of two counter-streaming components of magnetosheath-ty and (c) distributions with three components one of which has nearly zero parallel velocity and two counter-streaming components. Only the (a) type fits to the single magnetic flux tube formed by reconnection between magnetospheric and magnetosheath magnetic fields. We argue that two counter-streaming magnetosheath-like ion components observed by Interball within LLBL cannot be explained by the reflection of the ions from the magnetic mirror deeper within magnetosphere. Types (b) and (c) ion velocity distributions would form within spiral magnetic flux tube consisting of a mixture of alternating segments originating from the magnetosheath and from magnetospheric plasma. The shapes of ion velocity distributions and their evolution with decreasing number density in LLBL indicate that a significant part of LLBL is located on magnetic field lines of long spiral flux tube islands at the magnetopause, as has been proposed and found to occur in magnetopause simulations. We consider these observations as evidence for multiple reconnection X-ray lines between magnetosheath and magnetospheric flux tubes.
Vaisberg, O. L.↗
Searching for Turbulent Spectra in Mutliple Spacecraft Observations
The subject of magnetohydrodynamic simulations in the 1980's, magnetic turbulence has reemerged as a favored explanation for the production of fast magnetic reconnection. Recent three-dimensional simulations reveal the formation of secondary islands that serve to shorten the current sheet and increase the accelerating electric field, while both simulations and observations witness electron holes whose collapse energizes electrons. However, little work has been done to investigate the presence of turbulent magnetic and electric field spectra in association with in situ reconnection observations in space. In this study we address this deficiency by analyzing the wavelength spectra of two reconnection events established by multiple spacecraft observations in previous publications. We apply a k-filtering analysis to determine the wave vectors. To optimize the quality of the k-filtering analysis and minimize aliasing, we select multi-spacecraft observations having optimal spacecraft tetrahedral geometry and dimensions that resolve wavelengths within the ion diffusion region. We have chosen one dayside and one nightside reconnection event each observed by the Cluster spacecraft. Spatial correlation between the reconnecting current sheet and a turbulent magnetic spectrum supports an association between turbulence and reconnection in space. The k-filtering method, a wavelet time-frequency spectrum, and a polarization analysis serve to identify wave modes associated with the turbulence. A calculation of the reconnection electric field based on the normal component of the reconnecting magnetic field provides an estimate of the reconnection rate.
Wendel, Deirdre E.↗
Comparison of Magnetic Anomalies of Lithospheric Origin Measured by Satellite and Airborne Magnetometers over Western Canada
Crustal magnetic anomaly data from the OGO 2, 4 and 6 (Pogo) satellites are compared with upward-continued aeromagnetic data between 50 deg -85 deg N latitude and 220 deg - 260 deg E longitude. Agreement is good both in anomaly location and in amplitude, giving confidence that it is possible to proceed with the derivation and interpretation of satellite anomaly maps in all parts of the globe. The data contain a magnetic high over the Alpha ridge suggesting continental composition and a magnetic low over the southern Canada basin and northern Canadian Arctic islands (Sverdrup basin). The low in the Sverdrup basin corresponds to a region of high heat flow, suggesting a shallow Curie isotherm. A ridge of high field, with two distinct peaks in amplitude, is found over the northern portion of the platform deposits and a relative high is located in the central portion of the Churchill province. No features are present to indicate a magnetic boundary between Slave and Bear provinces, but a trend change is evident between Slave and Churchill provinces. South of 60 deg latitude a broad magnetic low is located over very thick (40-50 km) crust, interpreted to be a region of low magnetization.
Langel, R. A.↗
Investigation of solar active regions at high resolution by balloon flights of the solar optical universal polarimeter, definition phase
The definition phase of a scientific study of active regions on the sun by balloon flight of a former Spacelab instrument, the Solar Optical Universal Polarimeter (SOUP) is described. SOUP is an optical telescope with image stabilization, tunable filter and various cameras. After the flight phase of the program was cancelled due to budgetary problems, scientific and engineering studies relevant to future balloon experiments of this type were completed. High resolution observations of the sun were obtained using SOUP components at the Swedish Solar Observatory in the Canary Islands. These were analyzed and published in studies of solar magnetic fields and active regions. In addition, testing of low-voltage piezoelectric transducers was performed, which showed they were appropriate for use in image stabilization on a balloon.
Tarbell, Theodore D.↗
Comparisons of Long-Term Schumann Resonance Records in Europe and North America
Two stations at a distance comparable with the wavelength in the Schumann resonance (SR) frequency range, one in Europe (Nagycenk, Hungary) and one in North America (West Greenwich, Rhode Island) have simultaneously monitored the natural vertical electric and horizontal magnetic field components in the frequency range of 3-25 Hz. This is a unique opportunity, as Schumann resonance stations are scarce and even fewer station have records with 5-6 year durations. The main purpose of this paper is to make comparisons in the SR time series measured simultaneously at the two field site, thereby providing access to global behavior on the seasonal and interannual time scales. The comparative measurements described here point out distinct differences in the nature of convection in South America and in Africa and reveal new aspects about the behavior of tropical continental convection on the ENSO time scale.
Satori, G.↗
Mineral compositions of plutonic rocks from the Lewis Hills massif, Bay of Islands ophiolite
Mineral compositions of residual and cumulate rocks from the Lewis Hills massif of the Bay of Islands ophiolite complex are reported and interpreted in the context of magnetic processes involved in the geochemical evolution of spatially associated diabase dikes. The mineral compositions reflect greater degrees of partial melting than most abyssal peridotites do and appear to represent the most depleted end of abyssal peridotite compositions. Subsolidus equilibration between Cr-Al spinal and olivine generally has occurred at temperatures of 700 to 900 C. The spinel variations agree with the overall fractionation of basaltic magmas producing spinels with progressively lower Cr numbers. The compositions of clinopyroxenes suggest that the fractionation of two different magma series produced the various cumulate rocks.
Smith, Susan E.↗
High resolution studies of sunspots and flux tubes
This contract is for a three-year research study of sunspots and magnetic flux tubes in the solar atmosphere, using tunable filter images collected with a CCD camera during observing runs at the Canary Islands observatories in Spain. The best observations are analyzed and compared with theoretical models, to study the structure and dynamics of sunspots, their connections with surrounding magnetic fields, and the properties and evolution of smaller flux tubes in plage and quiet sun. Scientific results are reported at conferences and published in the appropriate journals. The contract is being performed by the Solar and Astrophysics Laboratory, part of the Lockheed Palo Alto Research Laboratory (LPARL) of the Research and Development Division (RDD) of Lockheed Missiles and Space Co., Inc. (LMSC). The principal investigator is Dr. Alan Title, and the research is done by him and other scientific staff at LPARL and Solar Physics Research Corporation (SPRC), often in collaboration with visiting scientists and students from other institutions. Highlights during this reporting period include completing the final version of a paper on the Evershed effect, writing a paper on magnetic diffusion, continuing work on contrast of small flux tubes, and work on the development of new models to interpret our sunspots observations.
Title, Alan↗
Longitudinal differences in electron precipitation near L = 4
The origin of the significant differences revealed in data on electron precipitation characteristics obtained above Siple Station, Antarctica, and Kerguelen Islands was investigated. The two stations are both in the Southern Hemisphere at nearly the same magnetic latitude (L=4) and at longitudes that place them roughly at equal distances east and west of the center of the South Atlantic magnetic anomaly. The primary data used in the study were counting rates from rocket-borne parachute-deployed scintillation counters and VLF data from ground-based and rocket-borne receivers. The two locations were found to differ in two major respects: (1) the precipitation background at Kerguelen Islands is very low, with high levels of wave activity being required to produce any detectable precipitation, and (2) X-ray microbursts, very common at Siple, were found to be essentially absent at Kerguelen. This observation supports models of the microburst generation process which predict maximum pitch angle scatterings of only a few tenths of a degree.
Bering, E. A., III↗
Radiative tearing - Magnetic reconnection on a fast thermal-instability time scale
Two energy modification mechanisms which are known to occur in sheared magnetic fields are the tearing and thermal instabilities. These processes can be studied separately with formalisms incorporating just the effective driving mechanism of interest (finite resistivity for the tearing mode and unstable radiation for the thermal mode). A model which includes both effects, and a temperature-dependent resistivity, indicates that modified forms of these two instabilities may coexist for identical physical conditions. When they are isolated computationally, one can show that their limiting growth rates are approximately those of the uncoupled instabilities. The spatial structure and energy content of these two new hybrid processes are then individually examined and are found to differ considerably from those obtained from separate treatments of the driving mechanisms. The faster radiative instability, which has a hydromagnetically scaled growth rate like the condensation mode of the thermal instability, is shown to involve a substantial amount of magnetic field reconnection. This can be partially explained by a large temperature drop (or resistivity rise) at the X-point. The island width of the Coulomb-coupled radiative mode is 30 percent of that produced by a comparable level of the slower tearing instability. In addition, the perturbed magnetic energy in the radiative instability is 5 times that of the perturbed thermal energy, indicating an appreciable modification of the initial magnetic structure.
Steinolfson, R. S.↗