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97 results on '"Simnett, G.M."'

1. Observations of CMEs from SOHO/LASCO

Author

Howard, R.A., primary, Brueckner, G.E., additional, St. Cyr, O.C., additional, Biesecker, D.A., additional, Dere, K.P., additional, Koomen, M.J., additional, Korendyke, C.M., additional, Lamy, P.L., additional, Llebaria, A., additional, Bout, M.V., additional, Michels, D.J., additional, Moses, J.D., additional, Paswaters, S.E., additional, Plunkett, S.P., additional, Schwenn, R., additional, Simnett, G.M., additional, Socker, D.G., additional, Tappin, S.J., additional, and Wang, D., additional

Published
2013
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11. Corotating Interaction Regions at High Latitudes

Author

Kunow, H., Lee, M.A., Fisk, L.A., Forsyth, R.J., Heber, B., Horbury, T.S., Keppler, E., Kóta, J., Lou, Y.-Q., McKibben, R.B., Paizis, C., Potgieter, M.S., Roelof, E.C., Sanderson, T.R., Simnett, G.M., Von Steiger, R., Tsurutani, B.T., Wimmer-Schweingruber, R.F., and Jokipii, J.R.

Published
1999
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14. Over the southern solar pole: low-energy interplanetary charged particles

Author

Lanzerotti, L.J., Armstrong, T.P., Gold, R.E., Maclennan, C.G., Roelof, E.C., Simnett, G.M., Thomson, D.J., Anderson, K.A., Hawkins, III, S.E., Krimigis, S.M., Lin, R.P., Pick, M., Sarris, E.T., and Tappin, S.J.

Subjects
Ulysses (Space probe) -- Observations, Sun -- Observations, Particles (Nuclear physics) -- Observations, Science and technology, Observations
Abstract

The heliosphere instrument for spectrum, composition, and anisotropy (HISCALE) recorded the fluxes of low-energy ions and electrons (>50 kiloelectron volts) when Ulysses crossed the southern solar polar region and revealed that the large-scale structure of the heliosphere to at least -75° was significantly influenced by the near-equatorial heliospheric current sheet. Electrons in particular were accelerated byte current sheet-produced and poleward-propagating interplanetary reverse shock at helioradii far from the Ulysses location. At heliolatitudes higher than -75° on the Ulysses ascent to the pole and -50° on the descent, small, less regular enhancements of the lowest energy electron fluxes were measured whose relations to the current sheet were less clear. The anomalous component of low-energy -2 to 5 megaelectron volts per nucleon) oxygen flux at the highest heliolatitudes was found to be [10.sup.-8] [per square centimeter per second per steradian (per kiloelectronvolt per nucleon)]; the anomalous Ne/O ratio was -0.25., The HISCALE investigation (1) on the Ulysses spacecraft provided three-dimensional measurements of the distributions of low-energy charged particles (electrons and ions with energies between 50 keV and 5 MeV) in [...]

Published
1995

15. The hot plasma environment at Jupiter: Ulysses results

Author

Lanzerotti, L.J., Armstrong, T.P., Gold, R.E., Anderson, K.A., Krimigis, S.M., Lin, R.P., Pick, M., Roelof, E.C., Sarris, E.T., Simnett, G.M., Maclennan, C.G., Choo, H.T., Tappin, S.J., and Zarka, P.

Subjects
Ulysses (Space probe) -- Observations, Plasma astrophysics -- Research, Jupiter (Planet) -- Observations -- Research, Magnetosphere -- Observations -- Research, Science and technology, Observations, Research
Abstract

Measurements of the hot plasma environment during the Ulysses flyby of Jupiter have revealed several new discoveries related to this large rotating astrophysical system. The Jovian magnetosphere was found by Ulysses to be very extended, with the day-side magnetopause located at [unkeyable] 105 Jupiter radii. The heavy ion (sulfur, oxygen, and sodium) population in the day-side magnetosphere increased sharply at [unkeyable] 86 Jupiter radii. This is somewhat more extended than the 'inner' magnetosphere boundary region identified by the Voyager hot plasma measurements. In the day-side magnetosphere, the ion fluxes have the anisotrophy direction expected for corotation with the planet, with the magnitude of the anisotrophy increasing when the spacecraft becomes more immersed in the hot plasma sheet. The relative abundances of sulfur, oxygen, and sodium to helium decreased somewhat with decreasing radial distance from the planet on the day-side, which suggests that the abundances of the Jupiter-derived species are dependent on latitude. In the dusk-side, high-latitude region, intense fluxes of counter-streaming ions and electrons were discovered from the edge of the plasma sheet to the dusk-side magnetopause. These beams of electrons and ions were found to be very tightly aligned with the magnetic field and to be superimposed on a time-and space-variable isotropic hot plasma background. The currents carried by the measured hot plasma particles are typically [unkeyable] 1.6 x [10.sup. -4] microamperes per square meter or [unkeyable] 8 x [10.sup.5] amperes per squared Jupiter radius throughout the high-latitude magnetosphere volume. It is likely that the intense particle beams discovered at high Jovian latitudes produce auroras in the polar caps of the planet., This report discusses the initial results obtained from measurements made by the HI-SCALE (heliosphere instrument for spectra, composition, and anisotropy at low energies) experiment as the Ulysses spacecraft traversed the [...]

Published
1992

20. Origin, Injection, and Acceleration of CIR Particles: Theory Report of Working Group 7

Author

Dept. of Atmospheric and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA, Astrophysikalisches Institut Potsdam, Potsdam, Germany, Institute for Problems of Mechanics, Russian Academy of Sciences, Moscow, Russia, Dept. of Astronomy and IPST, University of Maryland, College Park, Maryland, USA, Depts. of Planetary Sciences and Astronomy, University of Arizona, Tucson, Arizona, USA, International Space Science Institute, Bern, Switzerland, Max-Planck-Institut für Aeronomie, Katlenburg-Lindau, Germany, Extraterrestrische Physik, Universität Kiel, Kiel, Germany, Space Science Center, University of New Hampshire, Durham, New Hampshire, USA, Space Science Dept. of ESA ESTEC, Noordwijk, The Netherlands, Physics and Astronomy Dept., University of Birmingham, Birmingham, United Kingdom, Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany, Ann Arbor, Simnett, G.M., Kóta, J., Kallenbach, R., Scholer, M., Mann, G., Chalov, S., Desai, M.I., Fisk, Len A., Jokipii, J.R., Keppler, E., Kunow, H., Lee, M.A., Sanderson, T.R., Dept. of Atmospheric and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA, Astrophysikalisches Institut Potsdam, Potsdam, Germany, Institute for Problems of Mechanics, Russian Academy of Sciences, Moscow, Russia, Dept. of Astronomy and IPST, University of Maryland, College Park, Maryland, USA, Depts. of Planetary Sciences and Astronomy, University of Arizona, Tucson, Arizona, USA, International Space Science Institute, Bern, Switzerland, Max-Planck-Institut für Aeronomie, Katlenburg-Lindau, Germany, Extraterrestrische Physik, Universität Kiel, Kiel, Germany, Space Science Center, University of New Hampshire, Durham, New Hampshire, USA, Space Science Dept. of ESA ESTEC, Noordwijk, The Netherlands, Physics and Astronomy Dept., University of Birmingham, Birmingham, United Kingdom, Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany, Ann Arbor, Simnett, G.M., Kóta, J., Kallenbach, R., Scholer, M., Mann, G., Chalov, S., Desai, M.I., Fisk, Len A., Jokipii, J.R., Keppler, E., Kunow, H., Lee, M.A., and Sanderson, T.R.

Abstract

On the basis of the observational picture established in the report of Mason, von Steiger et al. (1999) the status of theoretical models on origin, injection, and acceleration of particles associated with Corotating Interaction Regions (CIRs) is reviewed. This includes diffusive or first-order Fermi acceleration at oblique shocks, adiabatic deceleration in the solar wind, stochastic acceleration in Alfvén waves and oblique propagating magnetosonic waves, and shock surfing as possible injection mechanism to discriminate pickup ions from solar wind ions.

Published
2006

21. Corotating Interaction Regions at High Latitudes

Author

Dept. of Atmospheric and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA, Extraterrestrische Physik, Universit??t Kiel, Kiel, Germany, Space Science Center, University of New Hampshire, Durham, New Hampshire, USA, The Blackett Laboratory, Imperial College, London, United Kingdom, Max-Planck-Institut f??r Aeronomie, Katlenburg-Lindau, Germany, The Blackett Laboratory, Imperial College, London, United Kingdom; Queen Mary and Westfield College, London, United Kingdom, Depts. of Planetary Sciences and Astronomy, University of Arizona, Tucson, Arizona, USA, Dipartimento di Fisica, Universit?? di, Milano, Milano, Italy, Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA, Potchefstroom University for CHE, Potchefstroom, South Africa, Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA, Space Science Dept.,???ESA/ESTEC, Noordwijk, The Netherlands, Physics and Astronomy Dept., University of Birmingham, Birmingham, United Kingdom, International Space Science Institute, Bern, Switzerland, Jet Propulsion Laboratory, Pasadena, California, USA, Physikalisches Institut der Universit??t Bern, Bern, Switzerland, Ann Arbor, Potgieter, M.S., Von Steiger, R., Sanderson, T.R., Kunow, H., Lee, M.A., Fisk, Len A., Heber, B., Keppler, E., Lou, Y.-Q., McKibben, R.B., Paizis, C., Roelof, E.C., Simnett, G.M., Tsurutani, B.T., Wimmer-Schweingruber, R.F., Jokipii, J.R., Forsyth, R.J., Horbury, T.S., K??ta, J., Dept. of Atmospheric and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA, Extraterrestrische Physik, Universit??t Kiel, Kiel, Germany, Space Science Center, University of New Hampshire, Durham, New Hampshire, USA, The Blackett Laboratory, Imperial College, London, United Kingdom, Max-Planck-Institut f??r Aeronomie, Katlenburg-Lindau, Germany, The Blackett Laboratory, Imperial College, London, United Kingdom; Queen Mary and Westfield College, London, United Kingdom, Depts. of Planetary Sciences and Astronomy, University of Arizona, Tucson, Arizona, USA, Dipartimento di Fisica, Universit?? di, Milano, Milano, Italy, Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA, Potchefstroom University for CHE, Potchefstroom, South Africa, Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA, Space Science Dept.,???ESA/ESTEC, Noordwijk, The Netherlands, Physics and Astronomy Dept., University of Birmingham, Birmingham, United Kingdom, International Space Science Institute, Bern, Switzerland, Jet Propulsion Laboratory, Pasadena, California, USA, Physikalisches Institut der Universit??t Bern, Bern, Switzerland, Ann Arbor, Potgieter, M.S., Von Steiger, R., Sanderson, T.R., Kunow, H., Lee, M.A., Fisk, Len A., Heber, B., Keppler, E., Lou, Y.-Q., McKibben, R.B., Paizis, C., Roelof, E.C., Simnett, G.M., Tsurutani, B.T., Wimmer-Schweingruber, R.F., Jokipii, J.R., Forsyth, R.J., Horbury, T.S., and K??ta, J.

Abstract

Ulysses observed a stable strong CIR from early 1992 through 1994 during its first journey into the southern hemisphere. After the rapid latitude scan in early 1995, Ulysses observed a weaker CIR from early 1996 to mid-1997 in the northern hemisphere as it traveled back to the ecliptic at the orbit of Jupiter. These two CIRs are the observational basis of the investigation into the latitudinal structure of CIRs. The first CIR was caused by an extension of the northern coronal hole into the southern hemisphere during declining solar activity, whereas the second CIR near solar minimum activity was caused by small warps in the streamer belt. The latitudinal structure is described through the presentation of three 26-day periods during the southern CIR. The first at???24??S shows the full plasma interaction region including fast and slow wind streams, the compressed shocked flows with embedded stream interface and heliospheric current sheet (HCS), and the forward and reverse shocks with associated accelerated ions and electrons. The second at 40??S exhibits only the reverse shock, accelerated particles, and the 26-day modulation of cosmic rays. The third at 60??S shows only the accelerated particles and modulated cosmic rays. The possible mechanisms for the access of the accelerated particles and the CIR-modulated cosmic rays to high latitudes above the plasma interaction region are presented. They include direct magnetic field connection across latitude due to stochastic field line weaving or to systematic weaving caused by solar differential rotation combined with non-radial expansion of the fast wind. Another possible mechanism is particle diffusion across the average magnetic field, which includes stochastic field line weaving. A constraint on connection to a distant portion of the CIR is energy loss in the solar wind, which is substantial for the relatively slow-moving accelerated ions. Finally, the weaker northern CIR is compared with the southern CIR. It is weak

Published
2006

23. CME-driven Coronal Shock Acceleration Of Energetic Electrons.

Author

Simnett, G.M. and Roelof, E.C.

Subjects
*SOLAR energy, *ELECTRONS, *CORONAL mass ejections
Abstract

53 impulsive (38–315 keV) near-relativistic solar electron events with beam-like pitch-angle distributions were observed by the ACE/EPAM experiment while the SOHO/LASCO coronographs were observing coronal mass ejections (CME) between 2.5 and 30 R⊙. Simnett, Roelof and Haggerty [in companion papers to be published in Ap. J., 2002] report a close association among the impulsive electron beams, solar electromagnetic emissions, and western hemisphere CMEs, jets, etc. They find that the electron injections are delayed ∼10 minutes after the electromagnetic emissions and ∼20 minutes after the CME launches, so that the electron release occurs when the CME has travelled 1–2 R⊙ beyond the CME launch altitude. The median exciter speed of the associated solar type III radio bursts (deduced from WIND/WAVES decametric spectrograms) is 0.08c, implying that the characteristic electron energies in the exciter front are only a few keV. Since no prompt near-relativistic electrons are injected until ∼10 minutes after the type III burst, the energy spectrum of the type III associated electrons must be steep at these energies. Therefore the near-relativistic electrons that must be present to produce the microwave and hard X-ray bursts also do not escape promptly with intensities measurable by ACE/EPAM. Inverse correlation between the finite delays of near-relativistic electrons after the CME launch confirms that the electrons are injected when the CMEs are ∼1–2 R⊙ above the photosphere. The positive correlation between CME speed and electron intensity (as well as spectral hardness) is consistent with the process of shock acceleration. Therefore we conclude that the simplest explanation of the observational associations is that the electrons are accelerated by CME-driven shocks in the corona at altitudes ∼1–2 R⊙ above the photosphere. We see no reason why ions should not also be accelerated concurrently in the corona by this same process, although the final velocity of the ions may be less than that of the electrons. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2003
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26. The solar mass ejection imager

Author

Jackson, B.V., primary, Buffington, A., additional, Hick, P., additional, Kahler, S.W., additional, Keil, S.L., additional, Altrock, R.C., additional, Simnett, G.M., additional, and Webb, D.F., additional

Published
1997
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30. Measurements of hot plasmas in the magnetosphere of Jupiter

Author

Lanzerotti, L.J., primary, Armstrong, T.P., additional, Maclennan, C.G., additional, Simnett, G.M., additional, Cheng, A.F., additional, Gold, R.E., additional, Thomson, D.J., additional, Krimigis, S.M., additional, Anderson, K.A., additional, Hawkins, S.E., additional, Pick, M., additional, Roelof, E.C., additional, Sarris, E.T., additional, and Tappin, S.J., additional

Published
1993
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35. Bulk flow velocities in the solar corona.

Author

Lewis, D.J. and Simnett, G.M.

Subjects
*SPEED, *SOLAR corona
Abstract

We present velocity estimates of bulk motions in the solar corona using data from the Large Angle Spectrometric Coronagraph (LASCO) aboard the Solar and Heliospheric Observatory spacecraft (SOHO). We describe a new technique which automatically provides a mass-weighted mean velocity profile in an entirely objective fashion without the need for individual event identification. A weighted velocity profile of this kind reflects the motion of the energetically dominant component of the coronal mass ejection (CME) mass spectrum and is of particular interest in consideration of the overall energy budget of the CME process. We consider the mean motion within three latitudinal bands centred at 0°, 20° and 40° over a one-year period around the time of solar minimum. We find terminal velocities within the LASCO field of around 300 km s[sup -1] in all latitude bands but note a latitudinal dependence in CME evolution through the low corona prior to reaching these velocities. We find evidence that ejections in the equatorial zone undergo continuous acceleration whilst at higher latitudes a discrete burst of acceleration is seen to occur at around 4 R[sub ⊙] from the Sun's centre with relatively little acceleration thereafter. We also consider the energy deposition rates necessary to generate these profiles. [ABSTRACT FROM AUTHOR]

Published
2000
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42. Solar maximum mission experiment: Early results of the hard X-ray imaging experiment

Author

Boelee, A., primary, de Jager, C., additional, Duijveman, A., additional, Galama, M., additional, Hoekstra, R., additional, Hoyng, P., additional, Imhof, J.P., additional, Lafleur, H., additional, Maseland, H.V.A.M., additional, Mels, W.A., additional, Schadee, A., additional, Schrijver, J., additional, Svestka, Z., additional, van Beek, H.F., additional, van Rens, P., additional, van der Laan, J.J.M., additional, van Tend, W., additional, Werkhoven, F., additional, Wiersma, G., additional, Zandee, W., additional, Simnett, G.M., additional, Charlton, C.P., additional, Fryer, R., additional, Willmore, A.P., additional, Wilson, J.W.G., additional, and Machado, M.E., additional

Published
1981
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