The EFW Instrument on the Cluster Satellites

List of Ongoing Science Projects, To add a new science project fill in this form.

Electric Field Structure in the Outer Cusp

Using data from all four spacecraft during crossings of the outer cusp, I'll be examining electric field structures with scale sizes comparable to the satellite separation distance and larger. Particular attention will be paid to vorticity in the electric field, and to features where the measured divergence is not zero. I am expecting to have some initial results ready in time for the EGS meeting at the end of March.

Project added 2001 - 2 - 23

SEVEM (Statistical ELF and VLF Environment Models)

We plan to use the CLUSTER wave observations to build global/statistical environmental models for the spatial distribution of VLF and ELF waves in the magnetosphere (mean intensities versus frequency, polarisation, propagation directions (!?), etc ...). These observations will be complemented with those from the DE mission already analysed at LPCE, Orleans, and Viking (currently under development at IASB).

Project added 2001 - 3 - 6

DC electric field at the magnetopause

The electric field at the magnetopause is studied, in particular the tangential electric field. The field is put into the magnetopause frame of reference using the magnetopause geometrical characteristics and motion as determined from multi-spacecraft comparisons.

Project added 2001 - 3 - 6

Large-amplitude auroral electric fields

A search is done for large (> approx 100 mV/m) electric fields on auroral field lines. The relation to upward/downward field aligned current regions and auroral emissions is studied. Spatio-temporal characteristics are deduced from multi-spacecraft observations to discriminate between stationary structures and waves.

Project added 2001 - 3 - 6

Field line resonances

Abstract submtitted to IAGA 2001: Field-line resonances are a direct consequence of the solar wind's interaction with a magnetized planet. They play a fundamental role in the coupling of the magnetosphere to the ionosphere. Initial results from multi-point observations by the Cluster spacecraft are presented. The emphasis is on the separation of temporal and spatial variations as well as on correlating the occurrence and characteristics of the resonances with the IMF.

Project added 2001 - 3 - 7

Cluster s/c potential calibration and use at boundaries

The s/c potential can provide high time resolution information about plasma density in solar wind, magnetosheath and inner magnetosphere/plasmasphere. In the plasmasheath and lobes and the outer cusp the spacecraft potential depends more on electron flux-this will require future calibrations with Cluster particle experiments.

Project added 2001 - 3 - 7

Power conversion (E.J) at the magnetopause

Power conversion can be identified for selected crossings of the magnetopause where the current density is established from four Cluster s/c and EFW can observe a clear electric field direction in this current layer. Observation of magnetopause orientation and motion is important for transforming electric fields to the magnetopause reference frame.

Project added 2001 - 3 - 7

Operation of the EFW experiment

By comparison of EFW data with flows from CIS, density from CIS, E-fields from EDI, etc., I will determine the quality, accuracy, and corrections for the EFW data. The corrections include a multiplying factor to account for the shorting of the field by the long, grounded, wire boom, an offset in the X-commponent of electric field, etc.

Project added 2001 - 3 - 20

EFW calibration studies

Comparisons of EFW determined electric fields with -VxB as determined from the FGM and CIS. These results will determine the effective antennae length.

Project added 2001 - 3 - 24

Boundary layer dynamics: solar wind/magnetosphere coupling

In the March-May time frame Cluster measurements concentrate on the cusp and mantle. At the same time in many cases, Polar will be skimming the magnetopause near apogee within a few hours in local time. These measurements may be nearby in the cusp, nearer the nose of the magnetopause, or in the cusp and boundary layers in the opposite hemisphere. Combining these data sets will provide new tools to address questions such as high-latitude versus subsolar merging, pulsed verses continuous merging, and the formation of and the open/closed character of the boundary layers.

Project added 2001 - 4 - 4

Cluster-Geotail and Cluster-POLAR conjunctions at nightside

To determine the power radiated from the tail in the form of low frequency electromagnetic waves and to assess its propagation down the field lines. Two point conjuctions with Geotail and POLAR spacecraft provide measurements of the Poynting flux at another altitude (other than Cluster's). IMAGE auroral oval images help place the events in global context.

Project added 2001 - 4 - 12

EFW Study of Shock Structure and Turbulence

I will study the density and electric field structure at the bow shock. I plan to compare the cross-shock potential with PEACE observations of electron heating. Part of this work will involve calculating shock speeds and thickness. I will also do a study of the (whistler?) turbulence observed in the layer.

Project added 2001 - 4 - 13

Correlation of broadband waves and anisotropic electrons

It is shown in a statistical study using POLAR data that anisotropic midenergetic electrons correlate well with broadband waves (1-10 Hz). The wavemodes are still however unknown. By using CLUSTER data we hope to be able to classify the wavemodes and in more detail study a possible interaction between the electrons and the waves.

Project added 2001 - 4 - 18

Correlative Studies of Ions and Fields on Cluster

We will carry out an investigation of the particle flows in the Earth's magnetosphere using ion plasma and ExB velocity measurements on the Cluster spacecraft. We hope to determine the accuracy with which these correlative observations can be made in order to set limits on the identification of non-MHD flows and boundary motions.

Project added 2001 - 4 - 20

2-D MHD turbulence near the plasmaspause

The Cluster quartet crosses the plasmasphere every ~2 days if the geomagnetic activity is not too high (in this case the plasmasphere may shrink to altitudes below L=4). The goal of this study is to detect and analyze the large fluctuations of the high resolution Spacecraft Potential, considered as a proxy of the electron density, measured by EFW near the plasmapause. The Whisper relaxation sounder data will be used as a complement below 100 e-/cc. From these data, different analysis tools will be used to check for the presence of 2-D MHD turbulence. This two-dimensional MHD turbulence could be produced by velocity shear at the flow separatrix which can be detected using the electric field data. The use of the 4 satellites facility will be used to look for spatial extension and temporal evolution of this turbulence. Finally, the relation between these large amplitude fluctuations and low frequency emissions observed by STAFF will be investigated.

Project added 2001 - 6 - 18

Study of plasma waves near the bow shock

I intend to investigate the evolution and dispersion of electromagnetic wave packets with distance from the bow shock and turbulence at the shock (fpe

Cluster instruments used:

EFW, WHISPER, STAFF

	Intervall 1	Intervall 2
Time intervalls:	2001.01.24.02-09	2001.02.19.10-20.18

Contact person:

om@so.estec.esa.nl

Olivier Moullard

------------------------> Position in the EFW society: associate

Further information can be found at:

Project added 2001 - 7 - 5

Wave Distribution Function Analysis on several spacecrafts

We investigate waves by reconstructing the wave distribution function from observed power and cross spectra. We use data from two or more of the Cluster II spacecrafts to reconstruct the distribution of wave energy in k-space.

Project added 2001 - 8 - 27

Investigation of Electron Phase Space Holes

Using a combination of electric field and particle data, the attributes and regions of occurrence of Electron-Phase-Space-Holes (EPSH) will be investigated and categorized, with particular attention to propagation and possible generation regions and/or mechanisms. Boundary layers such as the shock transition region as well as the cusp, plasma sheet , and the boundary layer plasma sheet will be investigated for EPSH, possible sources, and evidence of propagation.

Project added 2001 - 8 - 28

Auroral Zone Electric Fields and Density Irregularities

We are interested in studying the orientations, propagation speeds, thicknesses, and relative locations of electric field and density structures in the high-altitude auroral region, with the goal of understanding how the electric field and density structures are linked, and how the two together may control the mid-altitude auroral acceleration processes.

Project added 2001 - 8 - 29

Crossings of auroral oval during ground-based observations

Simultaneous measurements by the Cluster satellites and ground-based auroral cameras and photometers, magnetometers and radars (especially EISCAT Mainland and Svalbard radars) from the auroral oval will be looked for. The four spacecraft will allow to study the extent and temporal characteristics of auroral cavities and electric field fluctuations. Additional information about FACs, particles and high frequency waves would be valuable.

Project added 2001 - 9 - 4

Electromagnetic ion cyclotron waves

The electromagnetic ion cyclotron (EMIC) waves are among the most common waveforms in space, appearing in the different parts of the magnetosphere, magnetosheath and solar wind. The four Cluster satellites can give information about EMIC wave generation, their spatial extent, temporal development and propagation as well as their effects on particle populations.

Project added 2001 - 9 - 4

Auroral Alfén waves and broadband ELF emissions

We are studying the polarization, dispersive, propagation and poynting flux characteristics of low frequency Alfvénic and broadband ELF emissions (<300 Hz) within the auroral zone (including cusp). We will relate these emissions to current and density structures and look for the origin of these emission. Furthermore we hope to relate the observations to lower-altitude auroral acceleration processes. (Yes, we are in contact with John Bonnell)

Project added 2001 - 9 - 10

Magnetotail signatures of theta aurora

Utilizing Image and DMSP data to identify theta aurora (transpolar arcs) we will use Cluster to identify the magnetotail signatures associated with the TPAs.

Project added 2001 - 9 - 20

Multi-spacecraft study of energy transport by alfven waves

To use FAST and Cluster s/c to the propagation of Alfven waves in the near Earth magnetotail and cusp into the auroral oval. In this study observations from FAST and Cluster of Alfven waves and electron accleration will be compared and simulated to develop a model for energy transport by these waves in the high latitude magnetosphere

Project added 2002 - 1 - 10

Electric field and satellite potential measurements at the bow shock

The electric field and potential structure of Short Large Amplitude Magnetic Structures (SLAMS) at the Earth´s quasi-parallel bow shock is studied.

Project added 2002 - 1 - 14

Lobe cell convection and polar cap precipitation

We will seek observational evidence for magnetosheath plasma inside the magnetopause that is flowing sunward on magnetic field lines that map to low-altitude regions of sunward lobe cell convection and investigate whether particle precipition in these regions may cause signatures of transpolar aurora

Project added 2002 - 4 - 3

The response of the magnetosphere to pressure pulses

We are examining the response of the magnetosphere to pressure pulses, including the excitation of low frequency MHD waves and changes in the convection. In some cases, the waves are observed by Polar with Cluster as an upstream monitor in the magnetosheath. In some cases, the prime observations are on Cluster. This study uses the electric field, spacecraft potential and ExB velocities

Project added 2002 - 4 - 4

Studies of waveforms in the magnetotail and psb

We are studying the waveform capture observations made through out the magnetosphere. Our prime focus are waveforms in the magnetotail and low altitude plasma sheet. We are making comparisons with both plasma sheet crossings, the speed of the plasma sheet, and regions of large ExB flows. We are looking for cases where the near earth neutral line passed the satellite to examine the small-scale structures. This work is an outgrowth of our ISEE, Geotail and Polar studies. A paper is accepted in Tromso proceedings and one is submitted to ICS6 proceedings.

Project added 2002 - 4 - 4

The magnetopause at small scales

Investigation of the magnetopause from small scales (electron gyroradius and electron inertial length) up to mesoscales (ion gyroradius and ion inertial length)

Project added 2002 - 6 - 13

Broadband ELF emissions and energy transport in the cusp

We investigate the role of Broadband ELF emissions for energy transport in the polar cusp by analysis of electric and magnetic field wave data. The four spacecraft with small separation distances makes it plausible to infer some spatial information on the waves from cross-spectral analysis. Together with calculated Poynting flux, polarization and combined with particle data we try to answer questions like: the importance of these waves for energy transport to the ionosphere, the nature of the wave modes, the generation mechanism of broadband waves and the coupling of these phenomena to magnetic reconnection.

Project added 2002 - 6 - 13

Electric fields in the tail at substorm onset

Using magnetic and electric field data collected by the Cluster satellites near apogee, combined with ground-based observations from Canada and Scandinavia, I will try to identify signatures of predicted substorm instabilities in the mid-distant tail. By computing the spatial gradient tensors, large-scale field perturbations can be identified, and their relative motion established.

Project added 2002 - 6 - 13

Particle acceleration process above the dayside auroral region

It is known that the precipitating electrons are accelerated to downward by the strong parallel electric fields above the auroral region. This acceleration process occurs on not only the night side auroral region but on the dayside with high occurrence frequencies. Using the conjugated points observation between high altitudes (Cluster) satellite and low altitude (DMSP, FAST, Akebono etc.) satellite, we will see witch regions of the magnetosphere are related to the dayside auroral particle acceleration phenomena, and discuss their generation mechanisms.

Project added 2002 - 6 - 13

Lower hybrid cavities in plasmasphere and auroral zone

People: Anders Tjulin, Anders Eriksson, ... Object: Small-scale (ion gyroradius size) density depletions with enhanced wave activity in the lower hybrid frequency range. Background: Previously observed on Freja and several auroral sounding rockets, and in fact also found in the old Viking data set. We use the Cluster EFW internal burst data to study these in detail.

Project added 2002 - 9 - 27

Bow shock motions

Study of bow shock motions from normal and speeds determined by the timing methos and EFW SC potentiel

Project added 2002 - 10 - 9

Comparison of magnetospehric and ionospheric processes

We will investigate the variations of electric fields and related flow events in the magnetotail during periods with simultaneous (conjugate) ground-based (MIRACLE) observations. The large-structure and temporal evolution of the flow events will be examined by comparison with global MHD simulations.

Project added 2002 - 10 - 14

field-aligned accelration of O+ ions by the ponderomotive force

To explain the increase of bulk velocity of O+ ions parallel to the magnetic field, I'm estimating the ponderomotive force which affects on field-aligned motion of O+ ions under E-field waves existing. If there are E-field waves with frequencies of less than O+ ion gyrofrequency or around 0.1 Hz, the increase of field-aligned bulk velocity can be explained well. And with high time resolution data, for instance 0.04-sec interval, fine structure of bursty velocity increase can maybe explained also.

Project added 2003 - 2 - 4

Electric field properties in and near neutral sheet

Using data from all 4 Cluster S/C we study how electric field properties behave in and near the neutral sheet. Parameters to be investigated are 1) dawn-dusk electric field amplitude and 2) coherence/correlation of Edusk between spacecraft, both sorted by Bx and magnetic activity. The aim is to understand the characteristic temporal and spatial scales of E-field/plasma flow structures and how these are distributed around the neutral sheet.

Project added 2003 - 2 - 14

Energy and current transfer in the auroral magnetosphere

We plan to investigate potential generator regions in the high latitude auroral magnetosphere using conjugate data from Cluster and FAST. We shall examine the diversion of perpendicular currents into field-aligned currents and the current / energy transfer between the magnetosphere and the auroral ionosphere.

Project added 2003 - 10 - 31

Electric and magnetic field properties of foreshock ULF waves

The aim of this project is to combine EFW electric field data with FGM magnetic field data to extend on-going investigations into the properties of ion driven ULF waves in the terrestrial foreshock. The project will examine wave polarization, pointing flux, and use E and B data to determine intrinsic wave properties. The project will be limited to the study of ion driven foreshock wave phenomena, including shocklets and discrete wave packets, but not SLAMS. This project is complementary to Behlke's study of SLAMS, and also Moullard's project to study electron driven waves.

Project added 2004 - 3 - 16

Structure of oblique and non-laminar shock crossings

We have begun a preliminary investigation using FGM data into the nature of shock crossings where the profile at each spacecraft is not the same and the shock transition is often extended. This often corresponds to oblique/ quasi-parallel shock front geometry. We propose to use the EFW electric field and potential data together with magnetic data to study these extended shock transitions where a timing analysis cannot necessarily be applied. The projects of Bale and Maksimovic concentrate on the perpendicular shock where a timing analysis can be used; this project is complementary. Results from this project may also be of relevance to Behlke's study of SLAMS.

Project added 2004 - 3 - 16

Electric field in the inner magnetosphere

We plan to study the distribution of electric fields in the inner magnetosphere, in the region of possible overlap of cold plasmaspheric and hot RC/PS plasmas, in the context of SAPS and related phenomena in the ionoshere and the equatorial plane during disturbed conditions.

Project added 2004 - 10 - 25

Observation of plasma transfer event (PTE) seen by Cluster

Sonnerup et al. [GRL 2004] have described a flux transfer event (FTE) seen by Cluster on 2003/03/08. Using C1, C2, and C4 which were on the magnetosheath side of the magnetopause they could indentify FTE consisting of a flux rope of approximate size 1Re and irregular in shape embedded in the MP. The de Hoffmann-Teller (HT) frame mainly moves anti-sunward and northward, and is well anchored in the magnetosheath flow. They used C3 as well on the magnetospheric side, but the results are quite different. C3 saw a temperature minimum and gave a different HT frame. Several measured quantites with C3 not noted by the authors give a different view. CIS saw a burst of solar wind plasma (indentified by He++) at the time chosen by Sonnerup et al, coincident with plasma wave emissions detected by WHISPER. Electron data from PEACE varied also, with some field aligned flux. EFW showed electric field data which varied in unison with the ion and electron measurements suggesting a close relationship. AE had moderate acitivity reaching 100 nT. All these C3 and ground-based data are in agreement with a plasma transfer event (PTE) [Heikkila, JGR, 1997; Space Sci. Rev. 1998].

Project added 2004 - 11 - 8

Substorm of 2002/09/11 - 911 Plasmoid

The onset of an isolated substorm of 2002/09/11 began at 1600 UT in far north Finland (Kilpisjarvi). Cluster near apogee ~19 Re at midnight at z = -2 Re and saw nothing (except a decreasing value of Bz from 15 to 5 nT)until it apparently crossed a shock at 1623 UT into a plasmoid. RAPID data shows an immediate response with high fluxes of electrons and ions with high energies which lasted until 1740 UT. The data from the 4 s/c showed a nested structure. All instruments showed unique data (FGM, EFW, CIS, PEACE, and a variety of plasma emissions. A remarkable event!

Project added 2004 - 11 - 9

Structure of tail current sheet in flapping events

Multi-instrumental survey in the magnetotail of physical properties across the thickness of current sheets (with accurately known normals), moving quickly over the Cluster tetrahedron during intense flapping motions of the magnetotail plasma sheet.

Project added 2005 - 10 - 11