.png) |
| Our stars connection to the galactic current sheet is most evident during an eclipse |
NB* Professor Scott's mathematical model of a Birkeland Current.
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The fact that there could be a mix-up between spectrum lines for elements/molecular and lines in air with chemistry vs vacuum vs in denser plasmas with micro fields changes everything. Astrophysicists have no idea what is going on in the sun. They use purely physics, no chemistry, and their model treats the sun as an ideal gas not dense enough for chemistry despite acknowledging the magnetic fields everywhere, they treat it as a mysteriously magnetized gas.The Chromosphere & Second Solar Spectrum: Monitoring the Chemical Playground of the Sun!Is the Sun a Gas? The Standard Solar Model Explained!Is the Corona at MILLIONS of degrees?J.S. Ames, The Spectrum Researches of Professor J.M. Eder and E. Vallenta, Astrophys. J. 1895, 1, 443-446.M. Saha, Ionization of the Solar Chromosphere, Phil. Mag. 1920, 40, 479-488.J.A. Anderson, The Vacuum Spark Spectrum of Calcium, Astrophys. J. 1924, 59, 76-96. https://adsabs.harvard.edu/full/1924A...
C.M. Olmstead, Sun-Spot Bands Which Appear in the Spectrum of a Calcium Arc Burning in the Presence of Hydrogen, Astrophys. J., 1908, 27, 66-69. https://adsabs.harvard.edu/full/1908A...A.V. Demura, Physical Models of Plasma Microfield, Int. J. Spectros. 2010, 671073, pp42. https://www.hindawi.com/journals/ijs/...
H. Zirin, The mystery of the chromosphere. Solar Phys., 1996, v. 169,
G. Tsiropoula G., et al. Solar fine-scale structures I. Spicules and other small-scale, jet-like events at the chromospheric level: Observations and physical parameters. Space Sci. Rev. 2012, 169, 181–244.
P.M. Robitaille, The Liquid Metallic Hydrogen Model of the Sun and the Solar Atmosphere IV. On the Nature of the Chromosphere, Progress Phys. 2013, 3, L15-L21. http://www.ptep-online.com/2013/PP-34...
D. Nield, How Paint and a Speaker Could Explain The Physics of The Sun's Plasma Jets, March 13, 2022.
Spicules in H-AlphaCredit: Big Bear Solar Observatoryλ
J.O. Stenflo and C.U. Keller, New Window for Spectroscopy, Nature 1996, 382(6592), 588.
J.O. Stenflo and C.U. Keller, The Second Solar Spectrum. A new window for diagnostics of the Sun, Astro. Astrophysics 1997, 321, 927-934.
J.O. Stenflo et al., Anomalous polarization effects due to coherent scattering on the Sun. Astron. Astrophys. 2000, 355 789-803.
J.O. Stenflo, Polarization of the Sun’s continuous spectrum, A & A, 2005, 429, 713-730. https://www.aanda.org/articles/aa/pdf...
P.M. Robitaille, Polarized Light from the Sun: Unification of the Corona and Analysis of the Second Solar Spectrum – Further implications of a Liquid Metallic Hydrogen Solar Model, Progr. Phys. 2015, 11(3), 236-245.
Second Solar SpectrumA.M. Gandorfer, High Resolution Atlas of the Second Solar Spectrum, Istituto ricerche solari Aldo e Cele Daccò, Locarno.
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NIST lines dataSolar Fraunhofer Spectrum with assignmentsDigital Fraunhofer SpectrumSolar abundance data
2022 Geology/ cratersRobert Hawthorne Jr.
Professor Scott's mathematical model of a Birkeland Current.
NASA (Birkeland Currents)
Fujii, R.; Iijima, T.; Potemra, T. A.; Sugiura, M.
1981-01-01
Seasonal variations of large-scale Birkeland currents are examined in a study of the source mechanisms and the closure of the three-dimensional current systems in the ionosphere. Vector magnetic field data acquired by the TRIAD satellite in the Northern Hemisphere were analyzed for the statistics of single sheet and double sheet Birkeland currents during 555 passes during the summer and 408 passes during the winter. The single sheet currents are observed more frequently in the dayside of the auroral zone, and more often in summer than in winter. The intensities of both the single and double dayside currents are found to be greater in the summer than in the winter by a factor of two, while the intensities of the double sheet Birkeland currents on the nightside do not show a significant difference from summer to winter. Both the single and double sheet currents are found at higher latitudes in the summer than in the winter on the dayside. Results suggest that the Birkeland current intensities are controlled by the ionospheric conductivity in the polar region, and that the currents close via the polar cap when the conductivity there is sufficiently high. It is also concluded that an important source of these currents must be a voltage generator in the magnetosphere.
High altitude observations of Birkeland currents
NASA Technical Reports Server (NTRS)
Russell, C. T.
1977-01-01
Several models of field-aligned currents (Birkeland currents) in the magnetosphere are discussed, and high altitude observations of these currents, carried out with the aid of highly eccentric earth-orbiting spacecraft of the OGO and IMP series, are reviewed. The essential roles of Birkeland currents are identified: they relieve charge imbalances, transmit stresses, and lead to particle acceleration anomalous resistivity.
The effect of Birkeland currents on magnetic field topology
NASA Technical Reports Server (NTRS)
Peroomian, Vahe; Lyons, Larry R.; Schulz, Michael
1996-01-01
A technique was developed for the inclusion of large scale magnetospheric current systems in magnetic field models. The region 1 and 2 Birkeland current systems are included in the source surface model of the terrestrial magnetosphere. The region 1 and 2 Birkeland currents are placed in the model using a series of field aligned, infinitely thin wire segments. The normal component of the magnetic field from these currents is calculated on the surface of the magnetopause and shielded using image current carrying wires placed outside of the magnetosphere. It is found that the inclusion of the Birkeland currents in the model results in a northward magnetic field in the near-midnight tail, leading to the closure of previously open flux in the tail, and a southward magnetic field in the flanks. A sunward shift in the separatrix is observed.
Ionospheric and Birkeland current distributions inferred from the MAGSAT magnetometer data
NASA Technical Reports Server (NTRS)
Zanetti, L. J.; Potemra, T. A.; Baumjohann, W.
1983-01-01
Ionospheric and field-aligned sheet current density distributions are presently inferred by means of MAGSAT vector magnetometer data, together with an accurate magnetic field model. By comparing Hall current densities inferred from the MAGSAT data and those inferred from simultaneously recorded ground based data acquired by the Scandinavian magnetometer array, it is determined that the former have previously been underestimated due to high damping of magnetic variations with high spatial wave numbers between the ionosphere and the MAGSAT orbit. Among important results of this study is noted the fact that the Birkeland and electrojet current systems are colocated. The analyses have shown a tendency for triangular rather than constant electrojet current distributions as a function of latitude, consistent with the statistical, uniform regions 1 and 2 Birkeland current patterns.
Anderson, B. J.; Korth, H.; Waters, C. L.; ...
2014-05-07
The Active Magnetosphere and Planetary Electrodynamics Response Experiment uses magnetic field data from the Iridium constellation to derive the global Birkeland current distribution every 10 min. We examine cases in which the interplanetary magnetic field (IMF) rotated from northward to southward resulting in onsets of the Birkeland currents. Dayside Region 1/2 currents, totaling ~25% of the final current, appear within 20 min of the IMF southward turning and remain steady. In the onset of nightside currents occurs 40 to 70 min after the dayside currents appear. Afterwards, the currents intensify at dawn, dusk, and on the dayside, yielding a fullymore » formed Region 1/2 system ~30 min after the nightside onset. Our results imply that the dayside Birkeland currents are driven by magnetopause reconnection, and the remainder of the system forms as magnetospheric return flows start and progress sunward, ultimately closing the Dungey convection cycle.« less
The relationship of total Birkeland currents to the merging electric field
NASA Technical Reports Server (NTRS)
Bythrow, P. F.; Potemra, T. A.
1983-01-01
Magsat data were used to examine the behavior of Birkeland currents during 1100-2000 UT in consecutive orbits passing near the dawn-dusk meridian. The field was measured with a three-axis fluxgate instrument with a resolution of within 0.5 nT, with the sampling occurring every 1/16th sec. A total of 32 crossings of the Northern Hemisphere auroral zone were available for analysis. The changes in the magnetic readings were correlated more closely with variation in the IMF parameters than to the latitudinal width of the changes. Evidence was found for a relationship between the reconnection electric field and the intensity of the large-scale Birkeland current system. The total conductance of the auroral zone was calculated to be about 18.7 mhos.
Ionospheric convection inferred from interplanetary magnetic field-dependent Birkeland currents
NASA Technical Reports Server (NTRS)
Rasmussen, C. E.; Schunk, R. W.
1988-01-01
Computer simulations of ionospheric convection have been performed, combining empirical models of Birkeland currents with a model of ionospheric conductivity in order to investigate IMF-dependent convection characteristics. Birkeland currents representing conditions in the northern polar cap of the negative IMF By component are used. Two possibilities are considered: (1) the morning cell shifting into the polar cap as the IMF turns northward, and this cell and a distorted evening cell providing for sunward flow in the polar cap; and (2) the existence of a three-cell pattern when the IMF is strongly northward.
NASA Astrophysics Data System (ADS)
Coxon, John C.; Rae, I. Jonathan; Forsyth, Colin; Jackman, Caitriona M.; Fear, Robert C.; Anderson, Brian J.
2017-06-01
We conduct a superposed epoch analysis of Birkeland current densities from AMPERE (Active Magnetosphere and Planetary Electrodynamics Response Experiment) using isolated substorm expansion phase onsets identified by an independently derived data set. In order to evaluate whether R1 and R2 currents contribute to the substorm current wedge, we rotate global maps of Birkeland currents into a common coordinate system centered on the magnetic local time of substorm onset. When the latitude of substorm is taken into account, it is clear that both R1 and R2 current systems play a role in substorm onset, contrary to previous studies which found that R2 current did not contribute. The latitude of substorm onset is colocated with the interface between R1 and R2 currents, allowing us to infer that R1 current closes just tailward and R2 current closes just earthward of the associated current disruption in the tail. AMPERE is the first data set to give near-instantaneous measurements of Birkeland current across the whole polar cap, and this study addresses apparent discrepancies in previous studies which have used AMPERE to examine the morphology of the substorm current wedge. Finally, we present evidence for an extremely localized reduction in current density immediately prior to substorm onset, and we interpret this as the first statistical signature of auroral dimming in Birkeland current.
Relationship between Birkeland current regions, particle precipitation, and electric fields
NASA Technical Reports Server (NTRS)
De La Beaujardiere, O.; Watermann, J.; Newell, P.; Rich, F.
1993-01-01
The relationship of the large-scale dayside Birkeland currents to large-scale particle precipitation patterns, currents, and convection is examined using DMSP and Sondrestrom radar observations. It is found that the local time of the mantle currents is not limited to the longitude of the cusp proper, but covers a larger local time extent. The mantle currents flow entirely on open field lines. About half of region 1 currents flow on open field lines, consistent with the assumption that the region 1 currents are generated by the solar wind dynamo and flow within the surface that separates open and closed field lines. More than 80 percent of the Birkeland current boundaries do not correspond to particle precipitation boundaries. Region 2 currents extend beyond the plasma sheet poleward boundary; region 1 currents flow in part on open field lines; mantle currents and mantle particles are not coincident. On most passes when a triple current sheet is observed, the convection reversal is located on closed field lines.
Upward electron beams measured by DE-1 - A primary source of dayside region-1 Birkeland currents
NASA Technical Reports Server (NTRS)
Burch, J. L.; Reiff, P. H.; Sugiura, M.
1983-01-01
Measurements made by the High Altitude Plasma Instrument on DE-1 have shown that intense upward electron beams with energies from about 20 eV to about 200 eV are a common feature of the region just equatorward of the morning-side polar cusp. Computations of the currents carried by these beams and by the precipitating cusp electrons show excellent agreement with the simultaneous DE-1 magnetometer measurements for both upward and downward Birkeland currents. The data indicate that cold ionospheric electrons, which carry the downward region-1 Birkeland currents on the morning side, are accelerated upward by potential drops of a few tens of eV at altitudes of several thousand kilometers. This acceleration process allows spacecraft above those altitudes to measure routinely the charge carriers of both downward and upward current systems.
NASA Astrophysics Data System (ADS)
Anderson, Brian J.; Korth, Haje; Welling, Daniel T.; Merkin, Viacheslav G.; Wiltberger, Michael J.; Raeder, Joachim; Barnes, Robin J.; Waters, Colin L.; Pulkkinen, Antti A.; Rastaetter, Lutz
2017-02-01
Two of the geomagnetic storms for the Space Weather Prediction Center Geospace Environment Modeling challenge occurred after data were first acquired by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). We compare Birkeland currents from AMPERE with predictions from four models for the 4-5 April 2010 and 5-6 August 2011 storms. The four models are the Weimer (2005b) field-aligned current statistical model, the Lyon-Fedder-Mobarry magnetohydrodynamic (MHD) simulation, the Open Global Geospace Circulation Model MHD simulation, and the Space Weather Modeling Framework MHD simulation. The MHD simulations were run as described in Pulkkinen et al. (2013) and the results obtained from the Community Coordinated Modeling Center. The total radial Birkeland current, ITotal, and the distribution of radial current density, Jr, for all models are compared with AMPERE results. While the total currents are well correlated, the quantitative agreement varies considerably. The Jr distributions reveal discrepancies between the models and observations related to the latitude distribution, morphologies, and lack of nightside current systems in the models. The results motivate enhancing the simulations first by increasing the simulation resolution and then by examining the relative merits of implementing more sophisticated ionospheric conductance models, including ionospheric outflows or other omitted physical processes. Some aspects of the system, including substorm timing and location, may remain challenging to simulate, implying a continuing need for real-time specification.
Dominant modes of variability in large-scale Birkeland currents
NASA Astrophysics Data System (ADS)
Cousins, E. D. P.; Matsuo, Tomoko; Richmond, A. D.; Anderson, B. J.
2015-08-01
Properties of variability in large-scale Birkeland currents are investigated through empirical orthogonal function (EOF) analysis of 1 week of data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). Mean distributions and dominant modes of variability are identified for both the Northern and Southern Hemispheres. Differences in the results from the two hemispheres are observed, which are attributed to seasonal differences in conductivity (the study period occurred near solstice). A universal mean and set of dominant modes of variability are obtained through combining the hemispheric results, and it is found that the mean and first three modes of variability (EOFs) account for 38% of the total observed squared magnetic perturbations (δB2) from both hemispheres. The mean distribution represents a standard Region 1/Region 2 (R1/R2) morphology of currents and EOF 1 captures the strengthening/weakening of the average distribution and is well correlated with the north-south component of the interplanetary magnetic field (IMF). EOF 2 captures a mixture of effects including the expansion/contraction and rotation of the (R1/R2) currents; this mode correlates only weakly with possible external driving parameters. EOF 3 captures changes in the morphology of the currents in the dayside cusp region and is well correlated with the dawn-dusk component of the IMF. The higher-order EOFs capture more complex, smaller-scale variations in the Birkeland currents and appear generally uncorrelated with external driving parameters. The results of the EOF analysis described here are used for describing error covariance in a data assimilation procedure utilizing AMPERE data, as described in a companion paper.
Kristian Birkeland - The man and the scientist
NASA Technical Reports Server (NTRS)
Egeland, A.
1984-01-01
A review is presented of Birkeland's outstanding contributions to auroral theory and, in particular, to the foundation of modern magnetospheric physics. Birkeland's first years in research, after a study of mathematics and theoretical physics at the university, were concerned with Maxwell's theory, the investigation of electromagnetic waves in conductors, wave propagation in space, an energy transfer by means of electromagnetic waves, and a general expression for the Poynting vector. Experiments with cathode rays near a magnet in 1895, led Birkeland to the development of an auroral theory. This theory represented the first detailed, realistic explanation of the creation of an aurora. Attention is given to experiments conducted to verify the theory, the discovery of the polar elementary storm, and the deduction of auroral electric currents. Birkeland's background and education is also considered along with his personality.
NASA Astrophysics Data System (ADS)
Gustafsson, G.; Potemra, T. A.; Favin, S.; Saflekos, N. A.
1981-10-01
Principal oscillations of the TRIAD satellite are studied in 150 passes and are identified as the librations of a gravity-stabilized satellite. The libration periods are T(O)/2 and T(O)/(3) exp 1/2, where T(O) is the orbit period of about 100 min. The amplitude and phase change over periods of a few days, sometimes vanishing altogether, and these attitude changes are numerically evaluated and removed. Data from three consecutive passes spanning over three hours show a magnetic profile which extends as far as 10 deg in latitude from a single region 1 Birkeland current sheet, confirming the permanent and global nature of large-scale Birkeland currents.
Birkeland, Kristian (1868-1917)
NASA Astrophysics Data System (ADS)
Murdin, P.
2001-07-01
Birkeland was a Norwegian physicist, born in Oslo. In 1900, he identified and then simulated the charged electron-magnetic flux tube connection between the Sun and Earth that produces the aurora. He studied the zodiacal light during expeditions to the Sudan and Egypt. Birkeland committed suicide in a depression associated with the rejection of his auroral theories by his contemporary established...
Kristian Birkeland, The First Space Scientist
NASA Astrophysics Data System (ADS)
Egeland, A.; Burke, W. J.
2005-05-01
At the beginning of the 20th century Kristian Birkeland (1867-1917), a Norwegian scientist of insatiable curiosity, addressed questions that had vexed European scientists for centuries. Why do the northern lights appear overhead when the Earth's magnetic field is disturbed? How are magnetic storms connected to disturbances on the Sun? To answer these questions Birkeland interpreted his advance laboratory simulations and daring campaigns in the Arctic wilderness in the light of Maxwell's newly discovered laws of electricity and magnetism. Birkeland's ideas were dismissed for decades, only to be vindicated when satellites could fly above the Earth's atmosphere. Faced with the depleting stocks of Chilean saltpeter and the consequent prospect of mass starvation, Birkeland showed his practical side, inventing the first industrial scale method to extract nitrogen-based fertilizers from the air. Norsk Hydro, one of modern Norway's largest industries, stands as a living tribute to his genius. Hoping to demonstrate what we now call the solar wind, Birkeland moved to Egypt in 1913. Isolated from his friends by the Great War, Birkeland yearned to celebrate his 50th birthday in Norway. The only safe passage home, via the Far East, brought him to Tokyo where in the late spring of 1917 he passed away. Link: http://www.springeronline.com/sgw/cda/frontpage/0,11855,5-10100-22-39144987-0,00.html?changeHeader=true
.
Nordic cosmogonies: Birkeland, Arrhenius and fin-de-siècle cosmical physics
NASA Astrophysics Data System (ADS)
Kragh, Helge
2013-09-01
During the two decades before World War I, many physicists, astronomers and earth scientists engaged in interdisciplinary research projects with the aim of integrating terrestrial, solar and astronomical phenomena. Under the umbrella label "cosmical physics" they studied, for example, geomagnetic storms, atmospheric electricity, cometary tails and the aurora borealis. According to a few of the cosmical physicists, insights in solar-terrestrial and related phenomena might be extrapolated to the entire solar system or beyond it. Inspired by their research in the origin and
Fujii, R.; Iijima, T.; Potemra, T. A.; Sugiura, M.
1981-01-01
Seasonal variations of large-scale Birkeland currents are examined in a study of the source mechanisms and the closure of the three-dimensional current systems in the ionosphere. Vector magnetic field data acquired by the TRIAD satellite in the Northern Hemisphere were analyzed for the statistics of single sheet and double sheet Birkeland currents during 555 passes during the summer and 408 passes during the winter. The single sheet currents are observed more frequently in the dayside of the auroral zone, and more often in summer than in winter. The intensities of both the single and double dayside currents are found to be greater in the summer than in the winter by a factor of two, while the intensities of the double sheet Birkeland currents on the nightside do not show a significant difference from summer to winter. Both the single and double sheet currents are found at higher latitudes in the summer than in the winter on the dayside. Results suggest that the Birkeland current intensities are controlled by the ionospheric conductivity in the polar region, and that the currents close via the polar cap when the conductivity there is sufficiently high. It is also concluded that an important source of these currents must be a voltage generator in the magnetosphere.
High altitude observations of Birkeland currents
NASA Technical Reports Server (NTRS)
Russell, C. T.
1977-01-01
Several models of field-aligned currents (Birkeland currents) in the magnetosphere are discussed, and high altitude observations of these currents, carried out with the aid of highly eccentric earth-orbiting spacecraft of the OGO and IMP series, are reviewed. The essential roles of Birkeland currents are identified: they relieve charge imbalances, transmit stresses, and lead to particle acceleration anomalous resistivity.
The effect of Birkeland currents on magnetic field topology
NASA Technical Reports Server (NTRS)
Peroomian, Vahe; Lyons, Larry R.; Schulz, Michael
1996-01-01
A technique was developed for the inclusion of large scale magnetospheric current systems in magnetic field models. The region 1 and 2 Birkeland current systems are included in the source surface model of the terrestrial magnetosphere. The region 1 and 2 Birkeland currents are placed in the model using a series of field aligned, infinitely thin wire segments. The normal component of the magnetic field from these currents is calculated on the surface of the magnetopause and shielded using image current carrying wires placed outside of the magnetosphere. It is found that the inclusion of the Birkeland currents in the model results in a northward magnetic field in the near-midnight tail, leading to the closure of previously open flux in the tail, and a southward magnetic field in the flanks. A sunward shift in the separatrix is observed.
Ionospheric and Birkeland current distributions inferred from the MAGSAT magnetometer data
NASA Technical Reports Server (NTRS)
Zanetti, L. J.; Potemra, T. A.; Baumjohann, W.
1983-01-01
Ionospheric and field-aligned sheet current density distributions are presently inferred by means of MAGSAT vector magnetometer data, together with an accurate magnetic field model. By comparing Hall current densities inferred from the MAGSAT data and those inferred from simultaneously recorded ground based data acquired by the Scandinavian magnetometer array, it is determined that the former have previously been underestimated due to high damping of magnetic variations with high spatial wave numbers between the ionosphere and the MAGSAT orbit. Among important results of this study is noted the fact that the Birkeland and electrojet current systems are colocated. The analyses have shown a tendency for triangular rather than constant electrojet current distributions as a function of latitude, consistent with the statistical, uniform regions 1 and 2 Birkeland current patterns.
Anderson, B. J.; Korth, H.; Waters, C. L.; ...
2014-05-07
The Active Magnetosphere and Planetary Electrodynamics Response Experiment uses magnetic field data from the Iridium constellation to derive the global Birkeland current distribution every 10 min. We examine cases in which the interplanetary magnetic field (IMF) rotated from northward to southward resulting in onsets of the Birkeland currents. Dayside Region 1/2 currents, totaling ~25% of the final current, appear within 20 min of the IMF southward turning and remain steady. In the onset of nightside currents occurs 40 to 70 min after the dayside currents appear. Afterwards, the currents intensify at dawn, dusk, and on the dayside, yielding a fullymore » formed Region 1/2 system ~30 min after the nightside onset. Our results imply that the dayside Birkeland currents are driven by magnetopause reconnection, and the remainder of the system forms as magnetospheric return flows start and progress sunward, ultimately closing the Dungey convection cycle.« less
The relationship of total Birkeland currents to the merging electric field
NASA Technical Reports Server (NTRS)
Bythrow, P. F.; Potemra, T. A.
1983-01-01
Magsat data were used to examine the behavior of Birkeland currents during 1100-2000 UT in consecutive orbits passing near the dawn-dusk meridian. The field was measured with a three-axis fluxgate instrument with a resolution of within 0.5 nT, with the sampling occurring every 1/16th sec. A total of 32 crossings of the Northern Hemisphere auroral zone were available for analysis. The changes in the magnetic readings were correlated more closely with variation in the IMF parameters than to the latitudinal width of the changes. Evidence was found for a relationship between the reconnection electric field and the intensity of the large-scale Birkeland current system. The total conductance of the auroral zone was calculated to be about 18.7 mhos.
Ionospheric convection inferred from interplanetary magnetic field-dependent Birkeland currents
NASA Technical Reports Server (NTRS)
Rasmussen, C. E.; Schunk, R. W.
1988-01-01
Computer simulations of ionospheric convection have been performed, combining empirical models of Birkeland currents with a model of ionospheric conductivity in order to investigate IMF-dependent convection characteristics. Birkeland currents representing conditions in the northern polar cap of the negative IMF By component are used. Two possibilities are considered: (1) the morning cell shifting into the polar cap as the IMF turns northward, and this cell and a distorted evening cell providing for sunward flow in the polar cap; and (2) the existence of a three-cell pattern when the IMF is strongly northward.
NASA Astrophysics Data System (ADS)
Coxon, John C.; Rae, I. Jonathan; Forsyth, Colin; Jackman, Caitriona M.; Fear, Robert C.; Anderson, Brian J.
2017-06-01
We conduct a superposed epoch analysis of Birkeland current densities from AMPERE (Active Magnetosphere and Planetary Electrodynamics Response Experiment) using isolated substorm expansion phase onsets identified by an independently derived data set. In order to evaluate whether R1 and R2 currents contribute to the substorm current wedge, we rotate global maps of Birkeland currents into a common coordinate system centered on the magnetic local time of substorm onset. When the latitude of substorm is taken into account, it is clear that both R1 and R2 current systems play a role in substorm onset, contrary to previous studies which found that R2 current did not contribute. The latitude of substorm onset is colocated with the interface between R1 and R2 currents, allowing us to infer that R1 current closes just tailward and R2 current closes just earthward of the associated current disruption in the tail. AMPERE is the first data set to give near-instantaneous measurements of Birkeland current across the whole polar cap, and this study addresses apparent discrepancies in previous studies which have used AMPERE to examine the morphology of the substorm current wedge. Finally, we present evidence for an extremely localized reduction in current density immediately prior to substorm onset, and we interpret this as the first statistical signature of auroral dimming in Birkeland current.
Relationship between Birkeland current regions, particle precipitation, and electric fields
NASA Technical Reports Server (NTRS)
De La Beaujardiere, O.; Watermann, J.; Newell, P.; Rich, F.
1993-01-01
The relationship of the large-scale dayside Birkeland currents to large-scale particle precipitation patterns, currents, and convection is examined using DMSP and Sondrestrom radar observations. It is found that the local time of the mantle currents is not limited to the longitude of the cusp proper, but covers a larger local time extent. The mantle currents flow entirely on open field lines. About half of region 1 currents flow on open field lines, consistent with the assumption that the region 1 currents are generated by the solar wind dynamo and flow within the surface that separates open and closed field lines. More than 80 percent of the Birkeland current boundaries do not correspond to particle precipitation boundaries. Region 2 currents extend beyond the plasma sheet poleward boundary; region 1 currents flow in part on open field lines; mantle currents and mantle particles are not coincident. On most passes when a triple current sheet is observed, the convection reversal is located on closed field lines.
Upward electron beams measured by DE-1 - A primary source of dayside region-1 Birkeland currents
NASA Technical Reports Server (NTRS)
Burch, J. L.; Reiff, P. H.; Sugiura, M.
1983-01-01
Measurements made by the High Altitude Plasma Instrument on DE-1 have shown that intense upward electron beams with energies from about 20 eV to about 200 eV are a common feature of the region just equatorward of the morning-side polar cusp. Computations of the currents carried by these beams and by the precipitating cusp electrons show excellent agreement with the simultaneous DE-1 magnetometer measurements for both upward and downward Birkeland currents. The data indicate that cold ionospheric electrons, which carry the downward region-1 Birkeland currents on the morning side, are accelerated upward by potential drops of a few tens of eV at altitudes of several thousand kilometers. This acceleration process allows spacecraft above those altitudes to measure routinely the charge carriers of both downward and upward current systems.
NASA Astrophysics Data System (ADS)
Anderson, Brian J.; Korth, Haje; Welling, Daniel T.; Merkin, Viacheslav G.; Wiltberger, Michael J.; Raeder, Joachim; Barnes, Robin J.; Waters, Colin L.; Pulkkinen, Antti A.; Rastaetter, Lutz
2017-02-01
Two of the geomagnetic storms for the Space Weather Prediction Center Geospace Environment Modeling challenge occurred after data were first acquired by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). We compare Birkeland currents from AMPERE with predictions from four models for the 4-5 April 2010 and 5-6 August 2011 storms. The four models are the Weimer (2005b) field-aligned current statistical model, the Lyon-Fedder-Mobarry magnetohydrodynamic (MHD) simulation, the Open Global Geospace Circulation Model MHD simulation, and the Space Weather Modeling Framework MHD simulation. The MHD simulations were run as described in Pulkkinen et al. (2013) and the results obtained from the Community Coordinated Modeling Center. The total radial Birkeland current, ITotal, and the distribution of radial current density, Jr, for all models are compared with AMPERE results. While the total currents are well correlated, the quantitative agreement varies considerably. The Jr distributions reveal discrepancies between the models and observations related to the latitude distribution, morphologies, and lack of nightside current systems in the models. The results motivate enhancing the simulations first by increasing the simulation resolution and then by examining the relative merits of implementing more sophisticated ionospheric conductance models, including ionospheric outflows or other omitted physical processes. Some aspects of the system, including substorm timing and location, may remain challenging to simulate, implying a continuing need for real-time specification.
Dominant modes of variability in large-scale Birkeland currents
NASA Astrophysics Data System (ADS)
Cousins, E. D. P.; Matsuo, Tomoko; Richmond, A. D.; Anderson, B. J.
2015-08-01
Properties of variability in large-scale Birkeland currents are investigated through empirical orthogonal function (EOF) analysis of 1 week of data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). Mean distributions and dominant modes of variability are identified for both the Northern and Southern Hemispheres. Differences in the results from the two hemispheres are observed, which are attributed to seasonal differences in conductivity (the study period occurred near solstice). A universal mean and set of dominant modes of variability are obtained through combining the hemispheric results, and it is found that the mean and first three modes of variability (EOFs) account for 38% of the total observed squared magnetic perturbations (δB2) from both hemispheres. The mean distribution represents a standard Region 1/Region 2 (R1/R2) morphology of currents and EOF 1 captures the strengthening/weakening of the average distribution and is well correlated with the north-south component of the interplanetary magnetic field (IMF). EOF 2 captures a mixture of effects including the expansion/contraction and rotation of the (R1/R2) currents; this mode correlates only weakly with possible external driving parameters. EOF 3 captures changes in the morphology of the currents in the dayside cusp region and is well correlated with the dawn-dusk component of the IMF. The higher-order EOFs capture more complex, smaller-scale variations in the Birkeland currents and appear generally uncorrelated with external driving parameters. The results of the EOF analysis described here are used for describing error covariance in a data assimilation procedure utilizing AMPERE data, as described in a companion paper.
Kristian Birkeland - The man and the scientist
NASA Technical Reports Server (NTRS)
Egeland, A.
1984-01-01
A review is presented of Birkeland's outstanding contributions to auroral theory and, in particular, to the foundation of modern magnetospheric physics. Birkeland's first years in research, after a study of mathematics and theoretical physics at the university, were concerned with Maxwell's theory, the investigation of electromagnetic waves in conductors, wave propagation in space, an energy transfer by means of electromagnetic waves, and a general expression for the Poynting vector. Experiments with cathode rays near a magnet in 1895, led Birkeland to the development of an auroral theory. This theory represented the first detailed, realistic explanation of the creation of an aurora. Attention is given to experiments conducted to verify the theory, the discovery of the polar elementary storm, and the deduction of auroral electric currents. Birkeland's background and education is also considered along with his personality.
NASA Astrophysics Data System (ADS)
Gustafsson, G.; Potemra, T. A.; Favin, S.; Saflekos, N. A.
1981-10-01
Principal oscillations of the TRIAD satellite are studied in 150 passes and are identified as the librations of a gravity-stabilized satellite. The libration periods are T(O)/2 and T(O)/(3) exp 1/2, where T(O) is the orbit period of about 100 min. The amplitude and phase change over periods of a few days, sometimes vanishing altogether, and these attitude changes are numerically evaluated and removed. Data from three consecutive passes spanning over three hours show a magnetic profile which extends as far as 10 deg in latitude from a single region 1 Birkeland current sheet, confirming the permanent and global nature of large-scale Birkeland currents.
Birkeland, Kristian (1868-1917)
NASA Astrophysics Data System (ADS)
Murdin, P.
2001-07-01
Birkeland was a Norwegian physicist, born in Oslo. In 1900, he identified and then simulated the charged electron-magnetic flux tube connection between the Sun and Earth that produces the aurora. He studied the zodiacal light during expeditions to the Sudan and Egypt. Birkeland committed suicide in a depression associated with the rejection of his auroral theories by his contemporary established...
Kristian Birkeland, The First Space Scientist
NASA Astrophysics Data System (ADS)
Egeland, A.; Burke, W. J.
2005-05-01
At the beginning of the 20th century Kristian Birkeland (1867-1917), a Norwegian scientist of insatiable curiosity, addressed questions that had vexed European scientists for centuries. Why do the northern lights appear overhead when the Earth's magnetic field is disturbed? How are magnetic storms connected to disturbances on the Sun? To answer these questions Birkeland interpreted his advance laboratory simulations and daring campaigns in the Arctic wilderness in the light of Maxwell's newly discovered laws of electricity and magnetism. Birkeland's ideas were dismissed for decades, only to be vindicated when satellites could fly above the Earth's atmosphere. Faced with the depleting stocks of Chilean saltpeter and the consequent prospect of mass starvation, Birkeland showed his practical side, inventing the first industrial scale method to extract nitrogen-based fertilizers from the air. Norsk Hydro, one of modern Norway's largest industries, stands as a living tribute to his genius. Hoping to demonstrate what we now call the solar wind, Birkeland moved to Egypt in 1913. Isolated from his friends by the Great War, Birkeland yearned to celebrate his 50th birthday in Norway. The only safe passage home, via the Far East, brought him to Tokyo where in the late spring of 1917 he passed away. Link: http://www.springeronline.com/sgw/cda/frontpage/0,11855,5-10100-22-39144987-0,00.html?changeHeader=true
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Nordic cosmogonies: Birkeland, Arrhenius and fin-de-siècle cosmical physics
NASA Astrophysics Data System (ADS)
Kragh, Helge
2013-09-01
During the two decades before World War I, many physicists, astronomers and earth scientists engaged in interdisciplinary research projects with the aim of integrating terrestrial, solar and astronomical phenomena. Under the umbrella label "cosmical physics" they studied, for example, geomagnetic storms, atmospheric electricity, cometary tails and the aurora borealis. According to a few of the cosmical physicists, insights in solar-terrestrial and related phenomena might be extrapolated to the entire solar system or beyond it. Inspired by their research in the origin and