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Found 8 entries in the Bibliography.
Showing entries from 1 through 8
| 2018 |
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The stimulation of EMIC waves by a magnetospheric compression is perhaps the closest thing to a controlled experiment that is currently possible in magnetospheric physics, in that one prominent factor that can increase wave growth acts at a well-defined time. We present a detailed analysis of EMIC waves observed in the outer dayside magnetosphere by the four Magnetosphere Multiscale (MMS) spacecraft, Van Allen Probe A, and GOES 13, and by four very high latitude ground magnetometer stations in the western hemisphere before, during, and after a modest interplanetary shock on December 14, 2015. Analysis shows several features consistent with current theory, as well as some unexpected features. During the most intense MMS wave burst, which began ~ 1 min after the end of a brief magnetosheath incursion, independent transverse EMIC waves with orthogonal linear polarizations appeared simultaneously at all four spacecraft. He++ band EMIC waves were observed by MMS inside the magnetosphere, whereas almost all previous studies of He++ band EMIC waves observed them only in the magnetosheath and magnetopause boundary layers. Transverse EMIC waves also appeared at Van Allen Probe A and GOES 13 very near the times when the magnetic field compression reached their locations, indicating that the compression lowered the instability threshold to allow for EMIC wave generation throughout the outer dayside magnetosphere. The timing of the EMIC waves at both MMS and Van Allen Probe A was consistent with theoretical expectations for EMIC instabilities based on characteristics of the proton distributions observed by instruments on these spacecraft. Engebretson, M.; Posch, J.; Capman, N.; Campuzano, N.; elik, P.; Allen, R.; Vines, S.; Anderson, B.; Tian, S.; Cattell, C.; Wygant, J.; Fuselier, S.; Argall, M.; Lessard, M.; Torbert, R.; Moldwin, M.; Hartinger, M.; Kim, H.; Russell, C.; Kletzing, C.; Reeves, G.; Singer, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2018 YEAR: 2018 DOI: 10.1029/2018JA025984 |
| 2017 |
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Whistler-mode chorus waves are a naturally occurring electromagnetic emission observed in Earth\textquoterights magnetosphere. Here, for the first time, data from NASA\textquoterights Magnetospheric Multiscale (MMS) mission were used to analyze chorus waves in detail, including the calculation of chorus wave normal vectors, k. A case study was examined from a period of substorm activity around the time of a conjunction between the MMS constellation and NASA\textquoterights Van Allen Probes mission on 07 April 2016. Chorus wave activity was simultaneously observed by all six spacecraft over a broad range of L-shells (5.5 < L < 8.5), magnetic local time (06:00 < MLT < 09:00), and magnetic latitude (-32\textdegree < MLat < -15\textdegree), implying a large chorus active region. Eight chorus elements and their substructure were analyzed in detail with MMS. These chorus elements were all lower band and rising tone emissions, right-handed and nearly circularly polarized, and propagating away from the magnetic equator when they were observed at MMS (MLat ~ -31\textdegree). Most of the elements had \textquotedbllefthook\textquotedblright like signatures on their wave power spectra, characterized by enhanced wave power at flat or falling frequency following the peak, and all the elements exhibited complex and well organized substructure observed consistently at all four MMS spacecraft at separations up to 70 km (60 km perpendicular and 38 km parallel to the background magnetic field). The waveforms in field-aligned coordinates also demonstrated that these waves were all phase coherent allowing for the direct calculation of k. Error estimates on calculated k revealed that the plane wave approximation was valid for six of the eight elements and most of the subelements. The wave normal vectors were within 20-30\textdegree from the direction anti-parallel to the background field for all elements and changed from subelement to subelement through at least two of the eight elements. The azimuthal angle of k in the perpendicular plane was oriented earthward and was oblique to that of the Poynting vector, which has implications for the validity of cold plasma theory. Turner, D.; Lee, J.; Claudepierre, S.; Fennell, J.; Blake, J.; Jaynes, A.; Leonard, T.; Wilder, F.; Ergun, R.; Baker, D.; Cohen, I.; Mauk, B.; Strangeway, R.; Hartley, D.; Kletzing, C.; Breuillard, H.; Le Contel, O.; Khotyaintsev, Yu; Torbert, R.; Allen, R.; Burch, J.; Santolik, O.; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2017 YEAR: 2017 DOI: 10.1002/2017JA024474 chorus waves; inner magnetosphere; Magnetospheric multiscale; MMS; Radiation belts; Van Allen Probes |
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Storm time empirical model of O + and O 6+ distributions in the magnetosphere Recent studies have utilized different charge states of oxygen ions as a tracer for the origins of plasma populations in the magnetosphere of Earth, using O+ as an indicator of ionospheric-originating plasma and O6+ as an indicator of solar wind-originating plasma. These studies have correlated enhancements in O6+ to various solar wind and geomagnetic conditions to characterize the dominant solar wind injection mechanisms into the magnetosphere but did not include analysis of the temporal evolution of these ions. A sixth-order Fourier expansion model based empirically on a superposed epoch analysis of geomagnetic storms observed by Polar is presented in this study to provide insight into the evolution of both ionospheric-originating and solar wind-originating plasma throughout geomagnetic storms. At high energies (~200 keV) the flux of O+ and O6+ are seen to become comparable in the outer magnetosphere. Moreover, while the density of O+ is far higher than O6+, the two charge states have comparable pressures in the outer magnetosphere. The temperature of O6+ is generally higher than that of O+, because the O6+ is injected from preheated magnetosheath populations before undergoing further heating once in the magnetosphere. A comparison between the model results with O+ observations from the Magnetospheric Multiscale mission and the Van Allen Probes provides a validation of the model. In general, this empirical model agrees qualitatively well with the trends seen in both data sets. Quantitatively, the modeled density, pressure, and temperature almost always agree within a factor of at most 10, 5, and 2, respectively. Allen, R.; Livi, S.; Vines, S.; Goldstein, J.; Cohen, I.; Fuselier, S.; Mauk, B.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2017 YEAR: 2017 DOI: 10.1002/2017JA024245 MMS mission; Polar mission; solar wind injection; storm time dynamics; Van Allen Probes; Van Allen Probes mission |
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Previous observations have driven the prevailing assumption in the field that energetic ions measured by an instrument using a bare solid state detector (SSD) are predominantly protons. However, new near-equatorial energetic particle observations obtained between 7 and 12 RE during Phase 1 of the Magnetospheric Multiscale (MMS) mission challenge the validity of this assumption. In particular, measurements by the Energetic Ion Spectrometer (EIS) instruments have revealed that the intensities of heavy ion species (specifically oxygen and helium) dominate those of protons at energies math formula150-220 keV in the middle to outer (>7 RE) magnetosphere. Given that relative composition measurements can drift as sensors degrade in gain, quality cross-calibration agreement between EIS observations and those from the SSD-based Fly\textquoterights Eye Energetic Particle Spectrometer (FEEPS) sensors provides critical support to the veracity of the measurement. Similar observations from the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instruments aboard the Van Allen Probes spacecraft extend the ion composition measurements into the middle magnetosphere and reveal a strongly proton-dominated environment at math formula, but decreasing proton intensities at math formula. It is concluded that the intensity dominance of the heavy ions at higher energies (>150 keV) arises from the existence of significant populations of multiply-charged heavy ions, presumably of solar wind origin. Cohen, Ian; Mitchell, Donald; Kistler, Lynn; Mauk, Barry; Anderson, Brian; Westlake, Joseph; Ohtani, Shinichi; Hamilton, Douglas; Turner, Drew; Blake, Bern; Fennell, Joseph; Jaynes, Allison; Leonard, Trevor; Gerrard, Andrew; Lanzerotti, Louis; Allen, Robert; Burch, James; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2017 YEAR: 2017 DOI: 10.1002/2017JA024351 energetic ion composition; magnetospheric ion composition; Magnetospheric Multiscale (MMS); outer magnetosphere; ring current composition; suprathermal ions; Van Allen Probes |
| 2015 |
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We perform a statistical study of electromagnetic ion cyclotron (EMIC) waves detected by the Van Allen Probes mission to investigate the spatial distribution of their occurrence, wave power, ellipticity, and normal angle. The Van Allen Probes have been used which allow us to explore the inner magnetosphere (1.1 to 5.8 Re). Magnetic field measurements from the Electric and Magnetic Field Instrument Suite and Integrated Science onboard the Van Allen Probes are used to identify EMIC wave events for the first 22 months of the mission operation (8 September 2012 \textendash 30 June 2014). EMIC waves are examined in H+-, He+-, and O+-bands. Over 700 EMIC wave events have been identified over the three different wave bands (265 H+-band events, 438 He+-band events, and 68 O+-band events). EMIC wave events are observed between L = 2 \textendash 8, with over 140 EMIC wave events observed below L = 4. Results show that H+-band EMIC waves have two peak MLT occurrence regions: pre-noon (0900 < MLT <= 1200) and afternoon (1500 < MLT <= 1700) sectors. He+-band EMIC waves feature an overall stronger dayside occurrence. O+-band EMIC waves have one peak region located in the morning sector at lower L-shells (L < 4). He+-band EMIC waves average the highest wave power overall (>0.1 nT2/Hz), especially in the afternoon sector. Ellipticity observations reveal that linearly polarized EMIC wave dominate in lower L-shells. Saikin, A.; Zhang, J.-C.; Allen, R.C.; Smith, C.; Kistler, L.; Spence, H.; Torbert, R.; Kletzing, C.; Jordanova, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2015 YEAR: 2015 DOI: 10.1002/2015JA021358 EMIC waves; Fast Fourier Transform; spatial distribution; Van Allen Probes |
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A statistical study of EMIC waves observed by Cluster: 1. Wave properties Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, as well as local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the MLT-L frame within a limited MLAT range. In this study, we present a statistical analysis of EMIC wave properties using ten years (2001\textendash2010) of data from Cluster, totaling 25,431 minutes of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The statistical analysis is presented in two papers. This paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies. Allen, R.; Zhang, J.; Kistler, L.; Spence, H.; Lin, R.; Klecker, B.; Dunlop, M.; e, Andr\; Jordanova, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2015 YEAR: 2015 DOI: 10.1002/2015JA021333 |
| 2014 |
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Excitation of EMIC waves detected by the Van Allen Probes on 28 April 2013 We report the wave observations, associated plasma measurements, and linear theory testing of electromagnetic ion cyclotron (EMIC) wave events observed by the Van Allen Probes on 28 April 2013. The wave events are detected in their generation regions as three individual events in two consecutive orbits of Van Allen Probe-A, while the other spacecraft, B, does not detect any significant EMIC wave activity during this period. Three overlapping H+ populations are observed around the plasmapause when the waves are excited. The difference between the observational EMIC wave growth parameter (Σh) and the theoretical EMIC instability parameter (Sh) is significantly raised, on average, to 0.10 \textpm 0.01, 0.15 \textpm 0.02, and 0.07 \textpm 0.02 during the three wave events, respectively. On Van Allen Probe-B, this difference never exceeds 0. Compared to linear theory (Σh > Sh), the waves are only excited for elevated thresholds. Zhang, J.-C.; Saikin, A.; Kistler, L.; Smith, C.; Spence, H.; Mouikis, C.; Torbert, R.; Larsen, B.; Reeves, G.; Skoug, R.; Funsten, H.; Kurth, W.; Kletzing, C.; Allen, R.; Jordanova, V.; Published by: Geophysical Research Letters Published on: 06/2014 YEAR: 2014 DOI: 10.1002/2014GL060621 |
| 2013 |
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It is well accepted that the propagation of electromagnetic ion cyclotron (EMIC) waves are bidirectional near their source regions and unidirectional when away from these regions. The generally believed source region for EMIC waves is around the magnetic equatorial plane. Here we describe a series of EMIC waves in the Pc1 (0.2\textendash5 Hz) frequency band above the local He+ cyclotron frequency observed in situ by all four Cluster spacecraft on 9 April 2005 at midmagnetic latitudes (MLAT = ~33\textdegree\textendash49\textdegree) with L = 10.7\textendash11.5 on the dayside (MLT = 10.3\textendash10.4). A Poynting vector spectrum shows that the wave packets consist of multiple groups of packets propagating bidirectionally, rather than unidirectionally, away from the equator, while the local plasma conditions indicate that the spacecraft are entering into a region sufficient for local wave excitation. One possible interpretation is that, while part of the observed waves are inside their source region, the others are either close enough to the source region, or mixed with the wave packets from multiple source regions at different latitudes. Allen, R.; Zhang, J.; Kistler, L.; Spence, H.; Lin, R.; Dunlop, M.; e, Andr\; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2013 YEAR: 2013 DOI: 10.1002/jgra.50600 |
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