Waves around the lower hybrid frequency are frequently observed at Earth's magnetopause and readily reach very large amplitudes. Determining the properties of lower hybrid waves is crucial because ...they are thought to contribute to electron and ion heating, cross‐field particle diffusion, anomalous resistivity, and energy transfer between electrons and ions. All these processes could play an important role in magnetic reconnection at the magnetopause and the evolution of the boundary layer. In this paper, the properties of lower hybrid waves at Earth's magnetopause are investigated using the Magnetospheric Multiscale mission. For the first time, the properties of the waves are investigated using fields and direct particle measurements. The highest‐resolution electron moments resolve the velocity and density fluctuations of lower hybrid waves, confirming that electrons remain approximately frozen in at lower hybrid wave frequencies. Using fields and particle moments, the dispersion relation is constructed and the wave‐normal angle is estimated to be close to 90° to the background magnetic field. The waves are shown to have a finite parallel wave vector, suggesting that they can interact with parallel propagating electrons. The observed wave properties are shown to agree with theoretical predictions, the previously used single‐spacecraft method, and four‐spacecraft timing analyses. These results show that single‐spacecraft methods can accurately determine lower hybrid wave properties.
Key Points
The velocity and density fluctuations of magnetopause lower hybrid waves are resolved, showing that electrons are approximately frozen in
Lower hybrid wave dispersion relation and wave‐normal angle are computed from fields and particle measurements
Single‐ and multi‐spacecraft methods yield consistent lower hybrid wave properties, confirming the accuracy of single‐spacecraft methods
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
With the advent of the Heliophysics/Geospace System Observatory (H/GSO), a complement of multi-spacecraft missions and ground-based observatories to study the space environment, data retrieval, ...analysis, and visualization of space physics data can be daunting. The Space Physics Environment Data Analysis System (SPEDAS), a grass-roots software development platform (
www.spedas.org
), is now officially supported by NASA Heliophysics as part of its data environment infrastructure. It serves more than a dozen space missions and ground observatories and can integrate the full complement of past and upcoming space physics missions with minimal resources, following clear, simple, and well-proven guidelines. Free, modular and configurable to the needs of individual missions, it works in both command-line (ideal for experienced users) and Graphical User Interface (GUI) mode (reducing the learning curve for first-time users). Both options have “crib-sheets,” user-command sequences in ASCII format that can facilitate record-and-repeat actions, especially for complex operations and plotting. Crib-sheets enhance scientific interactions, as users can move rapidly and accurately from exchanges of technical information on data processing to efficient discussions regarding data interpretation and science. SPEDAS can readily query and ingest all International Solar Terrestrial Physics (ISTP)-compatible products from the Space Physics Data Facility (SPDF), enabling access to a vast collection of historic and current mission data. The planned incorporation of Heliophysics Application Programmer’s Interface (HAPI) standards will facilitate data ingestion from distributed datasets that adhere to these standards. Although SPEDAS is currently Interactive Data Language (IDL)-based (and interfaces to Java-based tools such as Autoplot), efforts are under-way to expand it further to work with python (first as an interface tool and potentially even receiving an under-the-hood replacement). We review the SPEDAS development history, goals, and current implementation. We explain its “modes of use” with examples geared for users and outline its technical implementation and requirements with software developers in mind. We also describe SPEDAS personnel and software management, interfaces with other organizations, resources and support structure available to the community, and future development plans.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Data from the NASA Magnetospheric Multiscale mission are used to investigate asymmetric magnetic reconnection at the dayside boundary between the Earth's magnetosphere and the solar wind. ...High‐resolution measurements of plasmas and fields are used to identify highly localized (~15 electron Debye lengths) standing wave structures with large electric field amplitudes (up to 100 mV/m). These wave structures are associated with spatially oscillatory energy conversion, which appears as alternatingly positive and negative values of J · E. For small guide magnetic fields the wave structures occur in the electron stagnation region at the magnetosphere edge of the electron diffusion region. For larger guide fields the structures also occur near the reconnection X‐line. This difference is explained in terms of channels for the out‐of‐plane current (agyrotropic electrons at the stagnation point and guide field‐aligned electrons at the X‐line).
Key Points
Energy conversion is highly localized within asymmetric reconnection electron diffusion regions
Oscillatory reconnection electric fields show characteristics of both spatial structures and propagating waves that are consistent with standing oblique quasi‐electrostatic whistlers
Both positive and negative values of J · E result from uniform current and oscillating electric fields
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
This paper reports on Magnetospheric Multiscale observations of whistler mode chorus and higher‐frequency electrostatic waves near and within a reconnection diffusion region on 23 November 2016. The ...diffusion region is bounded by crescent‐shaped electron distributions and associated dissipation just upstream of the X‐line and by magnetic field‐aligned currents and electric fields leading to dissipation near the electron stagnation point. Measurements were made southward of the X‐line as determined by southward directed ion and electron jets. We show that electrostatic wave generation is due to magnetosheath electron beams formed by the electron jets as they interact with a cold background plasma and more energetic population of magnetospheric electrons. On the magnetosphere side of the X‐line the electron beams are accompanied by a strong perpendicular electron temperature anisotropy, which is shown to be the source of an observed rising‐tone whistler mode chorus event. We show that the apex of the chorus event and the onset of electrostatic waves coincide with the opening of magnetic field lines at the electron stagnation point.
Key Points
Whistler mode chorus and higher‐frequency electrostatic waves were observed in the vicinity of a reconnection diffusion region at the dayside magnetopause
The location of the Earthward boundary of chorus and electrostatic waves coincides with the opening of magnetic field lines via reconnection
The causes of whistler mode chorus and electrostatic waves are shown to be electron temperature anisotropy and beam‐plasma interactions, respectively
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Plasma and wave measurements from the NASA Magnetospheric Multiscale mission are presented for magnetotail reconnection events on 3 July and 11 July 2017. Linear dispersion analyses were performed ...using distribution functions comprising up to six drifting bi‐Maxwellian distributions. In both events electron crescent‐shaped distributions are shown to be responsible for upper hybrid waves near the X‐line. In an adjacent location within the 3 July event a monodirectional field‐aligned electron beam drove parallel‐propagating beam‐mode waves. In the 11 July event an electron distribution consisting of a drifting core and two crescents was shown to generate upper‐hybrid and beam‐mode waves at three different frequencies, explaining the observed broadband waves. Multiple harmonics of the upper hybrid waves were observed but cannot be explained by the linear dispersion analysis since they result from nonlinear beam interactions.
Plain Language Summary
Magnetic reconnection is a process that occurs throughout the universe in ionized gases (plasmas) containing embedded magnetic fields. This process converts magnetic energy to electron and ion energy, causing phenomena such as solar flares and auroras. The NASA Magnetospheric Multiscale mission has shown that in magnetic reconnection regions there are intense electric field oscillations or waves and that electrons form crescent and beam‐like populations propagating both along and perpendicular to the magnetic field. This study shows that the observed electron populations are responsible for high‐frequency waves including their propagation directions and frequency ranges.
Key Points
Electron crescent‐shaped distributions produce upper hybrid waves in magnetotail reconnection events
Field‐aligned electron beams generate parallel electrostatic waves through the beam‐mode
Multiple crescent and convecting core distributions act together to produce broad frequency spectra as observed by MMS
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Electron inflow and outflow velocities during magnetic reconnection at and near the dayside magnetopause are measured using satellites from NASA's Magnetospheric Multiscale (MMS) mission. A case ...study is examined in detail, and three other events with similar behavior are shown, with one of them being a recently published electron‐only reconnection event in the magnetosheath. The measured inflow speeds of 200–400 km/s imply dimensionless reconnection rates of 0.05–0.25 when normalized to the relevant electron Alfvén speed, which are within the range of expectations. The outflow speeds are about 1.5–3 times the inflow speeds, which is consistent with theoretical predictions of the aspect ratio of the inner electron diffusion region. A reconnection rate of 0.04 ± 25% was obtained for the case study event using the reconnection electric field as compared to the 0.12 ± 20% rate determined from the inflow velocity.
Key Points
Electron inflow velocities are determined for reconnection at the magnetopause and in the magnetosheath
For four events inflow velocities of 200–400 km/s imply normalized reconnection rates of 0.05–0.25
Reconnection rates using electron inflow velocities (0.12) and the reconnection electric field (0.04) are compared for one event
Plain Language Summary
When the solar wind impacts the Earth's magnetosphere, an explosive energy conversion process called magnetic reconnection opens the door for solar wind energy to enter the magnetosphere by interconnection of the magnetic fields of the solar wind and of Earth. In this process, magnetic energy is converted to charged‐particle energy. Magnetic reconnection is fairly well understood at large scales and even down to the ion scale. However, the breaking and linking of field lines and the acceleration of electrons occur at much smaller scales, which are only recently being accessed by the NASA Magnetospheric Multiscale mission. This paper analyzes the speed at which electrons flow into and out of reconnection sites. The inflow speeds are crucial because they provide a measurement of the rate at which reconnection proceeds.
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Observations of magnetic reconnection at Earth's magnetopause often display asymmetric structures that are accompanied by strong magnetic field (B) fluctuations and large‐amplitude parallel electric ...fields (E||). The B turbulence is most intense at frequencies above the ion cyclotron frequency and below the lower hybrid frequency. The B fluctuations are consistent with a thin, oscillating current sheet that is corrugated along the electron flow direction (along the X line), which is a type of electromagnetic drift wave. Near the X line, electron flow is primarily due to a Hall electric field, which diverts ion flow in asymmetric reconnection and accompanies the instability. Importantly, the drift waves appear to drive strong parallel currents which, in turn, generate large‐amplitude (~100 mV/m) E|| in the form of nonlinear waves and structures. These observations suggest that turbulence may be common in asymmetric reconnection, penetrate into the electron diffusion region, and possibly influence the magnetic reconnection process.
Key Points
Asymmetric magnetic reconnection at the magnetopause often has strong magnetic field fluctuations and intense parallel electric fields
The magnetic field fluctuations are consistent with a thin, oscillating current sheet that is corrugated along the X line (drift wave)
The drift waves appear to drive strong parallel currents which, in turn, generate large‐amplitude parallel electric fields
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Data are analyzed from a Magnetospheric Multiscale encounter with a dayside magnetopause reconnection region on 29 December 2016. The uniqueness of the event stems from the small (~7 km) average ...spacecraft separation and the sequential sampling of an electron diffusion region with electron crescent distributions. We quantitatively investigate the earthward acceleration of magnetosheath electrons through the in‐plane null by the polarization electric field EN that points radially outward from the magnetopause. The results compare favorably with previous plasma simulations with one important difference that the reconnection electric field (EM) extends throughout the region of strong EN so that both fields energize electrons in the same region. This acceleration is quantified here for the first time. As the spacecraft penetrate deeper into the region of enhanced EN, the magnetic reflection of lower‐energy electrons produces a thinner crescent.
Plain Language Summary
Reconnection causes the conversion of magnetic energy to particle energy and the breaking and reconnection of solar wind and geomagnetic field lines. In asymmetric reconnection at the dayside magnetopause with different plasma densities and magnetic field strengths on the Earth and Sun sides of an X‐line, this energy conversion is displaced to the earthward side of the current layer. An electric field pointing outward normal to the dayside magnetopause drives reconnection by accelerating solar wind electrons across the reconnection current sheet. These electrons take up dawnward‐directed meandering orbits, and they are ultimately the carriers of the reconnection current. This paper reports the first direct measurement of this acceleration.
Key Points
Parallel and perpendicular energy conversion and electron acceleration are studied with data from four spacecraft with average separations of 7 km
The magnetopause normal electric field (EN) accelerates magnetosheath electrons across the reconnection current sheet to form crescent distributions
Magnetic reflection causes the crescent energy peaks to become narrower with increasing depth into the diffusion region
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
One of the major unresolved questions regarding the magnetic reconnection phenomenon is how plasma waves impact the process. In 2015, the National Aeronautics and Space Administration launched the ...four‐satellite Magnetospheric Multiscale Mission to study magnetic reconnection, especially on the electron scale. Since launch, it has identified several wave modes below the electron plasma frequency that occur near the dayside reconnection X‐line. These include large‐amplitude parallel electrostatic waves, whistler mode waves, lower hybrid waves, and turbulence associated with a corrugated current structure. We survey 23 electron diffusion region events observed by Magnetospheric Multiscale Mission at the dayside magnetopause to help understand how these wave modes impact the reconnection process. Common wave modes are identified, as well as their typical location within the reconnection layer (e.g., electron diffusion region, ion diffusion region, separatrix, and inflow and outflow jets). We find that, with a few exceptions, electromagnetic whistlers are most commonly confined to the separatrices of the exhaust boundary. Lower hybrid waves are found on the magnetosphere side of the current layer and do not make it to the X‐line. The wave modes that typically occur closest to the dissipation region are the corrugated current structures and large‐amplitude parallel electrostatic waves.
Key Points
We survey waves below the electron plasma frequency near 23 dayside magnetopause electron diffusion region events
The main waves investigated are whistlers, parallel electrostatic waves, current corrugation, and the lower hybrid drift instability
We find waves most typically occur on the magnetospheric side, with current corrugation most likely to reach the diffusion region
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Aims.In this paper, we present an innovative data reduction method for single-mode interferometry. It has been specifically developed for the AMBER instrument, the three-beam combiner of the Very ...Large Telescope Interferometer, but it can be derived for any single-mode interferometer. Methods.The algorithm is based on a direct modelling of the fringes in the detector plane. As such, it requires a preliminary calibration of the instrument in order to obtain the calibration matrix that builds the linear relationship between the interferogram and the interferometric observable, which is the complex visibility. Once the calibration procedure has been performed, the signal processing appears to be a classical least-square determination of a linear inverse problem. From the estimated complex visibility, we derive the squared visibility, the closure phase, and the spectral differential phase. Results.The data reduction procedures have been gathered into the so-called amdlib software, now available for the community, and are presented in this paper. Furthermore, each step in this original algorithm is illustrated and discussed from various on-sky observations conducted with the VLTI, with a focus on the control of the data quality and the effective execution of the data reduction procedures. We point out the present limited performances of the instrument due to VLTI instrumental vibrations which are difficult to calibrate.
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