S. Wellenzohn

University of Graz

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R. Nakamura

Austrian Academy of Sciences

R. B. Torbert

University of New Hampshire at Manchester

B. L. Giles

Goddard Space Flight Center

Y. V. Khotyaintsev

Swedish Institute of Space Physics

K. Torkar

Institute of Oncology Ljubljana

Peter Lindqvist

KTH Royal Institute of Technology

J. L. Burch

Southwest Research Institute

W. Baumjohann

Space Research Institute

R. E. Ergun

Laboratory for Atmospheric and Space Physics

S. Apatenkov

St Petersburg University

Cooperative Institutions

Austrian Academy of Sciences

Space Research Institute

University of Graz

University of California, Los Angeles

Goddard Space Flight Center

Planetary Science Institute

Institute of Space and Astronautical Science

Charles River Laboratories (Netherlands)

Southwest Research Institute

Swedish Institute of Space Physics

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Estimation of the Electron Density From Spacecraft Potential During High‐Frequency Electric Field Fluctuations

Journal of Geophysical Research Space Physics (2020)

Owen Roberts R. Nakamura K. Torkar D. B. Graham D. J. Gershman

Spacecraft potential has often been used to infer electron density with much higher time resolution than is typically possible with plasma instruments. However, recently two studies by Torkar et al. 2017 and Graham et al. 2018 have shown that external electric fields can also have an effect on the spacecraft potential by enhancing photoelectron escape from the surface. Consequently, should the electron density derived from the spacecraft potential be used during an event with a large electric field, the estimation would be contaminated and the user would see the effects of the electric field rather than density perturbations. The goal of this paper is to propose a method to remove the electric field effects to allow the density derived from spacecraft potential to be used even during large amplitude wave events such as Langmuir waves or upper hybrid waves.

Spacecraft charging

Langmuir Probe

10.1029/2020ja027854

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Characteristics of energy dispersion of ions and electrons in the PSBL flows during substorms

EGUGA (2019)

S. Wellenzohn R. Nakamura Victor Sergeev A. Varsani S. Apatenkov

Electron precipitation

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CME volume calculation from 3D GCS reconstruction

Lukas Holzknecht Manuela Temmer Mateja Dumbović S. Wellenzohn K. Krikova

The mass evolution of a coronal mass ejection (CME) is an important parameter characterizing the drag force acting on a CME as it propagates through interplanetary space. Spacecraft measure in-situ plasma densities of CMEs during crossing events, but for investigating the mass evolution, we also need to know the CME geometry, more specific, its volume. Having derived the CME volume and mass from remote sensing data using 3D reconstructed CME geometry, we can calculate the CME density and compare it with in-situ proton density measurements near Earth. From that we may draw important conclusions on a possible mass increase as the CME interacts with the ambient solar wind in the heliosphere. In this paper we will describe in detail the method for deriving the CME volume using the graduated cylindrical shell (GCS) model (Thernisien et al., 2006,2009, see Figure 1). We show that, assuming self-similar expansion, one can derive the volume of the CME from two GCS parameters and that it furthermore can be expressed as a function of distance.

Heliosphere

Interplanetary medium

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CME volume calculation from 3D GCS reconstruction

arXiv (Cornell University) (2019)

Lukas Holzknecht Manuela Temmer Mateja Dumbović S. Wellenzohn K. Krikova

10.48550/arxiv.1904.11418

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Remote Sensing of Magnetic Reconnection in the Magnetotail Using In Situ Multipoint Observations at the Plasma Sheet Boundary Layer

Journal of Geophysical Research Space Physics (2020)

S. Wellenzohn R. Nakamura Takuma Nakamura A. Varsani В. А. Сергеев

Abstract Characteristics of the reconnection region are examined based on Magnetospheric Multiscale (MMS) observation of a plasma sheet boundary layer crossing on July 12, 2018 when both high‐energy (>few keV) electrons as well as ions flowing parallel to the magnetic field showed distinct energy dispersion. Remote sensing techniques are applied to estimate location of reconnection region and injection time of these particles. The reconnection region is estimated to be located at X = (−23 ± 1.9) R E from electrons, comparable to that from ions, X = (−24.5 ± 0.7) R E by taking into account the time of flight effect as well as the effect of separatrix motion relative to the plasma. The electron injection times precede that of ions by ∼6 s. We found that the time dispersed energetic electron beams away from X‐line are accompanied by short‐lived high‐frequency parallel‐electric field disturbances around plasma frequency. These wave packets are the first observable remote feature of reconnection. Using multi‐point measurements of high energy ions, electrons, magnetic field, and parallel‐electric field disturbances, reconnection electric field is estimated as 1.6–2.5 mV/m initially and decrease to ∼0.8 mV/m within ∼20 s. This study shows that the remote sensing scheme is an alternative method to infer the temporal/spatial changes of the magnetotail reconnection.

Plasma sheet

Current sheet

Field line

10.1029/2020ja028917

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MMS observations of reconnection separatrix region in the magnetotail at different distances from the active neutral X-line

В. А. Сергеев S. Apatenkov R. Nakamura S. Wellenzohn Ferdinand Plaschke

<p>The region surrounding the reconnection separatrix consists of the multitude of particle and wave transient features (electron, cold and hot ion beams, Hall E&B fields, kinetic Alfven and LH waves, e-holes etc) whose pattern and intensities may vary depending on the stage of reconnection process as well as on the distance from the active neutral line (XNL), whose characterization from observations is not a trivial task. We explore quick MMS entries into the plasma sheet boundary layer from the lobe in 2017 and 2018 tail seasons which potentially could be the crossings of the active separatrix as suggested by energy dispersed beams and polar rain gap features. By combining &#160;the observations of beam dispersion with the measured plasma convection and PSBL motion (obtained using the timing method) we attempt to separate &#160;temporal and spatial (velocity filter) contributions &#160;to the observed beam energy dispersion and evaluate the MMS distance from the XNL. In this report we discuss similarities and differences of separatrix manifestations &#160;observed far from the XNL (at distances exceeding several tens Re) and those found close to it (where the outermost electron beam directed toward the XNL is seen). &#160;One of surprizes was that we were often able to identify the intense Hall-like E&B field structures at very large distances from the XNL. &#160;</p>

Separatrix

Line (geometry)

10.5194/egusphere-egu2020-4615

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Plasma density estimates from spacecraft potential using MMS observations in the dayside magnetosphere

M. Andriopoulou R. Nakamura S. Wellenzohn K. Torkar W. Baumjohann

Using spacecraft potential observations with and without active spacecraft potential control (on/off) from the Magnetospheric Multiscale (MMS) mission, we estimate the average photoelectron emissio ...

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Improved Determination of Plasma Density Based on Spacecraft Potential of the Magnetospheric Multiscale Mission Under Active Potential Control

IEEE Transactions on Plasma Science (2019)

K. Torkar R. Nakamura S. Wellenzohn H. Jeszenszky R. B. Torbert

Data from the Magnetospheric Multiscale (MMS) mission, in particular, the spacecraft potential measured with and without the ion beams of the active spacecraft potential control (ASPOC) instruments, plasma electron moments, and the electric field, have been employed for an improved determination of plasma density based on spacecraft potential. The known technique to derive plasma density from spacecraft potential sees the spacecraft behaving as a plasma probe which adopts a potential at which the ambient plasma current and one of photoelectrons produced at the surface and leaving into space are in equilibrium. Thus, the potential is a function of the plasma current, and plasma density can be determined using measurements or assumptions on plasma temperature. This method is especially useful during periods when the plasma instruments are not in operation or when spacecraft potential data have significantly higher time resolution than particle detectors. However, the applicable current-voltage characteristic of the spacecraft has to be known with high accuracy, particularly when the potential is actively controlled and shows only minor residual variations. This paper demonstrates recent refinements of the density determination coming from: 1) the reduction of artifacts in the potential data due to the geometry of the spinning spacecraft and due to effects of the ambient electric field on the potential measurements and 2) a calibration of the plasma current to the spacecraft surfaces which is only possible by comparison with the variable currents from the ion beams of ASPOC. The results are discussed, and plasma densities determined by this method are shown in comparison with measurements by the Fast Plasma Instrument (FPI) for some intervals of the MMS mission.

Spacecraft charging

Astrophysical plasma

10.1109/tps.2019.2911425

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Field‐Aligned Currents Originating From the Magnetic Reconnection Region: Conjugate MMS‐ARTEMIS Observations

Geophysical Research Letters (2018)

A. V. Artemyev P. L. Pritchett V. Angelopoulos X.‐J. Zhang R. Nakamura

Abstract Near‐Earth magnetic reconnection reconfigures the magnetotail and produces strong plasma flows that transport plasma sheet particles and electromagnetic energy to the inner magnetosphere. An essential element of such a reconfiguration is strong, transient field‐aligned currents. These currents, believed to be generated within the plasma sheet and closed at the ionosphere, are responsible for magnetosphere‐ionosphere coupling during substorms. We use conjugate measurements from Magnetospheric Multiscale (MMS) at the plasma sheet boundary (around x ∼− 10 R E ) and Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) at the equator (around x ∼− 60 R E ) to explore the potential generation region of these currents. We find a clear correlation between the field‐aligned current intensity measured by MMS and the tailward plasma sheet flows measured by ARTEMIS. To better understand the origin of this correlation, we compare spacecraft observations with results from 3‐D particle‐in‐cell simulations of magnetotail reconnection. The comparison reveals that field‐aligned currents and plasma flows start, wax, and wane due to the development of a reconnection region between MMS (near‐Earth) and ARTEMIS (at lunar distance). A weak correlation between the field‐aligned current intensity at MMS and earthward flow magnitudes at ARTEMIS suggests that distant magnetotail reconnection does not significantly contribute to the generation of the observed near‐Earth currents. Our findings support the idea that the dominant role of the near‐Earth magnetotail reconnection in the field‐aligned current generation is likely responsible for their transient nature, whereas more steady distant tail reconnection would support long‐term field‐aligned current system.

Substorm

Current sheet

Plasma sheet

10.1029/2018gl078206

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Plasma density estimates from spacecraft potential using MMS observations in the dayside magnetosphere

AGU Fall Meeting Abstracts (2016)

M. Andriopoulou R. Nakamura S. Wellenzohn K. Torkar W. Baumjohann

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