453 research outputs found
Carriers and sources of magnetopause current: MMS Case Study
No full textWe investigate the current carriers and current sources of an ion scale tangential magnetopause current layer using the Magnetospheric Multiscale four spacecraft data. Within this magnetopause current layer, ions and electrons equally contribute to the perpendicular current, while electrons carry nearly all the parallel current. The energy range of all these current carriers is predominantly from middle to high (>100 eV), where particles with higher energies are more efficient in producing the current. By comparing each term, two-fluid magnetohydrodynamic (MHD) theory is able to describe the current sources to a large degree because the sum of all the perpendicular currents from MHD theory could account for the currents observed. In addition, we find that the ion diamagnetic current is the main source of the total perpendicular current, while the curvature current can be neglected. Nevertheless, ions and electrons both carry comparable current due to the redistribution of the electric field and show features beyond the classic Chapman-Ferraro model, particularly on the front side of the boundary layer where the electric field reversal is most intense. We also show a second, comparative event in which ions do not satisfy MHD theory, while the electrons do. The small-scale, adiabatic parameter (square of curvature radius/gyroradius) supports our interpretation that this second event contains ion scale substructure. We suggest that comparing the predicted MHD current with plasma current can be a good method to judge whether the MHD theory is satisfied in each specific circumstance, especially for high-precision Magnetospheric Multiscale data.</p
Electron acceleration observed by the FAST satellite within the IAR during a 3 Hz modulated EISCAT heater experiment
No full textInternational audienceA quantitative analysis is presented of the FAST satellite electric field and particle flux data during an EISCAT heating experiment run on 8 October 1998. Radio frequency heating, modulated at 3 Hz, launched ULF waves from the ionosphere into the lower magnetosphere. The ULF waves were observed in FAST data and constituted the first satellite detection of artificially excited Alfvénic ULF waves. The downward electron flux data for this event contain the first observations of electrons undergoing acceleration within the Ionospheric Alfvén Resonator (IAR) due to parallel electric fields associated with an artificially stimulated Alfvén wave. The time history and spectral content of the observed down-ward electron fluxes is investigated by considering the effects of a localised parallel electric field. Furthermore, it is demonstrated that a power law electron energy distribution describes the time-variable observed fluxes better than a Maxwellian distribution
Observation of high-frequency electrostatic waves in the vicinity of the reconnection ion diffusion region by the spacecraft of the Magnetospheric Multiscale (MMS) mission
No full textAuthors: - M. Zhou, M. Ashour-Abdalla, J. Berchem, R. J. Walker, H. Liang, M. El-Alaoui, M. L. Goldstein, P.-A. Lindqvist, G. Marklund, Y. V. Khotyaintsev, R. E. Ergun, F. D. Wilder, C. T. Russell, R. J. Strangeway, C. Zhao, W. R. Paterson, B. L. Giles, C. J. Pollock, R. B. Torbert, J. L. Burch, J. C. Dorelli, D. J. Gershman, L. A. Avanov, B. Lavraud, M. O. ChandlerWe report Magnetospheric Multiscale observations of high-frequency electrostatic waves in the vicinity of the reconnection ion diffusion region on the dayside magnetopause. The ion diffusion region is identified during two magnetopause crossings by the Hall electromagnetic fields, the slippage of ions with respect to the magnetic field, and magnetic energy dissipation. In addition to electron beam modes that have been previously detected at the separatrix on the magnetospheric side of the magnetopause, we report, for the first time, the existence of electron cyclotron harmonic waves at the magnetosheath separatrix. Broadband waves between the electron cyclotron and electron plasma frequencies, which were probably generated by electron beams, were found within the magnetopause current sheet. Contributions by these high-frequency waves to the magnetic energy dissipation were negligible in the diffusion regions as compared to those of lower-frequency waves.This research was supported by NASA Magnetospheric Multiscale Mission Interdisciplinary Scientist grant NNX08AO48G, NASA Heliospheric Grand Challenge grant NNX14AI16G, and NSF grant AGS-1450864. IRAP contribution to MMS was supported by CNES and CNRS. We thank the entire MMS team and instrument leads for data access and support. M.Z. appreciates D. Schriver and H.Y. Wei for their valuable discussions. The data presented in this paper are the L2 data of MMS and can be accessed from MMS Science Data Center (https://lasp.colorado.edu/mms/sdc/public/).https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2016GL06901
Coalescence of Macroscopic Flux Ropes at the Subsolar Magnetopause: Magnetospheric Multiscale Observations
No full textAuthors: - M. Zhou, J. Berchem, R. J. Walker, M. El-Alaoui, X. Deng, E. Cazzola, G. Lapenta, Melvyn Goldstein, W. R. Paterson, Y. Pang, R. E. Ergun, B. Lavraud, H. Liang, C. T. Russell, R. J. Strangeway, C. Zhao, B. L. Giles, C. J. Pollock, P.-A. Lindqvist, G. Marklund, F. D. Wilder, Y. V. Khotyaintsev, R. B. Torbert, and J. L. BurchWe report unambiguous in situ observation of the coalescence of macroscopic flux ropes by the magnetospheric multiscale (MMS) mission. Two coalescing flux ropes with sizes of ∼ 1 RE
were identified at the subsolar magnetopause by the occurrence of an asymmetric quadrupolar signature in the normal component of the magnetic field measured by the MMS spacecraft. An electron diffusion region (EDR) with a width of four local electron inertial lengths was embedded within the merging current sheet. The EDR was characterized by an intense parallel electric field, significant energy dissipation, and suprathermal electrons. Although the electrons were organized by a large guide field, the small observed electron pressure nongyrotropy may be sufficient to support a significant fraction of the parallel electric field within the EDR. Since the flux ropes are observed in the exhaust region, we suggest that secondary EDRs are formed further downstream of the primary reconnection line between the magnetosheath and magnetospheric fields.We thank T. Phan and N. Bessho for valuable suggestions. This research was supported by NASA
Magnetospheric Multiscale Mission Interdisciplinary
Scientist Grant No. NNX08AO48G, NASA Grant
No. NNX15AI92G, and NSF Grant No. AGS-1450864.
Work in China was supported by the National Natural
Science Foundation of China (NSFC) under Grants No. 41331070 and No. 41522405 and Science Foundation
of Jiangxi Province (Grant No. 20142BCB23006). EC
acknowledges financial support from the Leverhulme Trust
Research Project Grant No. 2014-112. We thank the entire
MMS team and instrument PIs for data access and support,https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.05510
Comment on “Joule heating by ac electric fields in the ionosphere of Venus” by K. D. Cole and W. R. Hoegy
No full textControl and choice in English prisons: developing health-promoting prisons.
No full textThe 'health-promoting prison' has been informed by a broader settings-based philosophy to health promotion which conceptualizes health as the responsibility for all social settings. Though in its relative infancy, the notion of a health-promoting prison has gained political backing from international organizations like the World Health Organization, but the implementation of the policy rhetoric has not translated across all prison environments. The aim of this paper is to consider how key elements of health promotion discourse-choice, control and implicitly, empowerment-can apply in the context of imprisonment. These concepts were examined in three category-C (secure) prisons in England, through interviews with 36 male prisoners and 19 prison staff conducted by the first author. Analysis showed that prisoners negotiated the norms, structures and strictures of prison life by both relinquishing control and also by taking control, showing resistance and exercising some element of choice. The paradox is that, as most prisoners are expected to be released at some point they need to exercise some agency, control and choice, but these learning experiences may be constrained whilst 'inside'. The paper argues that if a settings approach in prison is truly to move forward, both conceptually and practically, then health promoters should seek to embed the key values of health promotion within the prison setting
Two-Dimensional Velocity of the Magnetic Structure Observed on July 11, 2017 by the Magnetospheric Multiscale Spacecraft
No full textIn order to determine particle velocities and electric field in the frame of the magnetic structure, one first needs to determine the velocity of the magnetic structure in the frame of the spacecraft observations. Here, we demonstrate two methods to determine a two-dimensional magnetic structure velocity for the magnetic reconnection event observed in the magnetotail by the Magnetospheric Multiscale (MMS) spacecraft on July 11, 2017, Spatio-Temporal Difference (STD) and the recently developed polynomial reconstruction method. Both of these methods use the magnetic field measurements; the reconstruction technique also uses the current density measured by the particle instrument. We find rough agreement between the results of our methods and with other velocity determinations previously published. We also explain a number of features of STD and show that the polynomial reconstruction technique is most likely to be valid within a distance of 2 spacecraft spacings from the centroid of the MMS spacecraft. Both of these methods are susceptible to contamination by magnetometer calibration errors
Magnetospheric Multiscale Observations of an Ion Diffusion Region With Large Guide Field at the Magnetopause: Current System, Electron Heating, and Plasma Waves
No full textAuthors: - M. Zhou, J. Berchem, R. J. Walker, M. El-Alaoui, M. L. Goldstein, G. Lapenta, X. Deng, J. Li, O. Le Contel, D. B. Graham, B. Lavraud, W. R. Paterson, B. L. Giles, J. L. Burch, R. B. Torbert, C. T. Russell, R. J. Strangeway, C. Zhao, R. E. Ergun, P.-A. Lindqvist, G. MarklundWe report Magnetospheric Multiscale (MMS) observations of a reconnecting current sheet in the presence of a weak density asymmetry with large guide field at the dayside magnetopause. An ion diffusion region (IDR) was detected associated with this current sheet. Parallel current dominated over the perpendicular current in the IDR, as found in previous studies of component reconnection. Electrons were preferentially heated parallel to the magnetic field within the IDR. The heating was manifested as a flattop distribution below 400 eV. Two types of electromagnetic electron whistler waves were observed within the regions where electrons were heated. One type of whistler wave was associated with nonlinear structures in E|| with amplitudes up to 20 mV/m. The other type was not associated with any structures in E||. Poynting fluxes of these two types of whistler waves were directed away from the X-line. We suggest that the nonlinear evolution of the oblique whistler waves gave rise to the solitary structures in E||. There was a perpendicular super-Alfvénic outflow jet that was carried by magnetized electrons. Intense electrostatic lower hybrid drift waves were localized in the current sheet center and were probably driven by the super-Alfvénic electron jet, the velocity of which was approximately equal to the diamagnetic drift of demagnetized ions. Our observations suggest that the guide field significantly modified the structures (Hall electromagnetic fields and current system) and wave properties in the IDR.This research was supported by NASA HGCR 80NSSC17K0014, and NSF grant AGS-1450864. Work in China was supported by the National Natural Science Foundation of China (NSFC) under grants 41331070, 41522405, and 41774154. The French involvement (SCM instruments) on MMS is supported by CNES, CNRS-INSIS, and CNRS-INSU. We thank the entire MMS team and instrument PIs for data access and support. The MMS data can be accessed from MMS Science Data Center (https://lasp.colorado.edu/mms/sdc/public/). The OMNI data are provided by the space physics data facility of Goddard space flight center (https://spdf.gsfc.nasa.gov/data_orbits.html).https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2017JA02451
An investigation of the field-aligned current associated with a large-scale ULF wave in the morning sector,, Planet. Space Sci., 55, 770, 2007.
No full textPrevious work by Scoffield, H.C., Yeoman, T.K., Wright, D.M., Milan, S.E., Wright, A.N., Strangeway, R.J. [2005. An investigation of the field aligned currents associated with a large scale ULF wave using data from CUTLASS and FAST. Ann. Geophys. 23, 487-498) investigated a large-scale ULF wave, occurring in the dusk sector (-1900MLT). The wave had a period of similar to 800s (corresponding to 1.2mHz frequency), an azimuthal wave number of similar to 7 and a full-width at half-maximum (FWHM) across the resonance of 350km. IMAGE ground magnetometer and SuperDARN radar observations of the wave's spatial and temporal characteristics were used to parameterise a simple, two-dimensional field line resonance (FLR) model. The model-calculated field-aligned current (FAC) was compared with FACs derived from the FAST energetic particle spectra and magnetic field measurement. Here the authors use the same method to investigate the FAC structure of a second large-scale ULF wave, with a period of similar to 450 s, occurring the dawn sector (similar to 0500 MLT) with an opposite sense background region 1-region 2 current system. This wave has a much larger longitudinal scale (m similar to 4.5) and a smaller latitude scale (FWHM = 150 km). Unlike the dusk sector wave, which was dominated by upward FAC, FAST observations of the dawn sector wave show an interval of large-scale downward FAC of similar to 1.5 mu A m(-2). Downgoing magnetospheric electrons with energies of a few kcV were observed, which are associated with upward FACs of similar to 1 mu A m(-2). For both wave studies, downward currents appear to be carried partially by upgoing electrons below the FAST energy detection threshold (5eV), but also consist of a mixture of hotter downgoing magnetospheric electrons and upgoing ionospheric electrons of energies 30 eV-1 keV. Strong intervals of upward current show that small-scale structuring of scale similar to 50 km has been imposed on the current carriers. In general, this study confirms the findings of Scoffield, H.C., Yeoman, T.K., Wright, D.M., Milan, S.E., Wright, A.N., Strangeway, R.J. [2005. An investigation of the FACs associated with a large-scale ULF wave using data from CUTLASS and FAST. Ann. Geophys. 23, 487-498). (c) 2006 Elsevier Ltd. All rights reserved.</p
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