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PEACE Team Meeting 2010
Cluster and Double Star PEACE

MSSL, 6th-8th March 2012

List of Abstracts (Authors)

1	Steve Schwartz et al.	Electron Temperature Gradient Scale at Collisionless Shocks
2	Chris Gurgiolo et al.	Direct Observations of the Formation of the Solar Wind Halo from the Strahl
3	Chris Gurgiolo et al.	Preliminary Results: Characteristics of the Taylor Microscale In the Solar Wind: Magnetic Field and Electron Velocity Measurements
4	Melvin Goldstein et al.	The Curious Relationship Between the Electron Strahl and the Dissipation of Electromagnetic Turbulence in the Solar Wind
5	Wai-Leong Teh et al.	Electron Dynamics in Reconnection Ion Diffusion Region
6	Dominique Fontaine et al.	Synthesis of the work done on the particle percipitation and outflows above the polar cap arcs during periods of northward IMF
7	Lucile Turc et al.	Magnetic cloud structure before and after the bow shock crossing - First aproach
8	Chris Arridge et al.	Survey of anisotropic electron moments in Saturn's magnetosphere
9	Matt Taylor et al.	Spatial distribution of rolled up Kelvin-Helmholtz vortices at Earth's dayside and flank magnetopause
10	Jan Soucek et al.	Electron scale observations of solar wind magnetic holes and associated high frequency wave emissions
11	Colin Forsyth et al.	Temporal evolution and electric potential structure of the auroral acceleration region from multi-spacecraft measurements
12	Robert Fear et al.	High latitude observations of magnetotail plasma-sheet plasma in conjunction with a transpolar arc
13	Robert Fear et al.	Seasonal control of the location of flux transfer events signatures at the magnetopause
14	Malcolm Dunlop et al.	Magnetopause Reconnection Across Wide Local Time
15	Andrew Walsh et al.	Characteristics of the Solar Wind Electron Distribution at 10AU
16	Andrew Walsh et al.	Dawn-Dusk Asymmetries in Average Magnetotail Pitch Angle Distributions
17	David Winningham et al.	Three Planet View of Electron Bow Shock Acceleration
18	Jeremy Mitchell et al.	Bowshock Heating and Magnetosheath Electron Communication
19	Roger Duthie et al.	BBFs & Dipolarisations : Substorm related phenomena of the terrestrial magnetotail
20	Branislav Mihaljčić et al.	Cluster Penetrating Radiation Studies
21	Roger Duthie et al.	Cross-Calibration & Hybridisation of Data from Cluster Spacecraft to Probe the Magnetotail Plasma Sheet
22	George Parks et al.	Parallel electric field and solar wind
23	David Winningham et al.	Parallel electric field and solar wind
24	Sandrine Grimald et al.	Statistical study of the NTC plasmaspheric patches: a direct link between wave observation in the inner magnetosphere and magnetic activity
25	Michael Balikhin et al.	Title Magnetic holes in the vicinity of dipolarisation fronts: Mirror or Tearing structures?
26	Michael Balikhin et al.	The analysis of electron fluxes at geosynchronous orbit.
27	Sandrine Grimald et al.	Study of the applicability of the curlometer technique with the four Cluster spacecraft in regions close to Earth

Abstracts In Detail

Steve Schwartz et al.

Steven J. Schwartz, Edmund Henley, Jeremy Mitchell
Blackett Laboratory, Imperial College London, South Kensington, London SW7 2AZ, UK
and
Vladimir Krasnoselskikh
Laboratoire de Physique et Chimie de l'Environnement, CNRS, Orleans, France

Electron Temperature Gradient Scale at Collisionless Shocks

Shock waves are ubiquitous in astrophysics and interplanetary space. In collisionless plasmas they transform directed flow energy into thermal energy and accelerate energetic particles. The energy repartition amongst particle populations is a multi-scale process related to the spatial and temporal structure of the electromagnetic fields within the shock layer. While major features of the large scale ion heating are known, the electron heating and smaller scale fields remain poorly understood and controversial. We determine for the first time the scale of the electron temperature gradient via unprecedented high time resolution electron distributions measured in situ by the Cluster spacecraft. We discover that half of the electron heating coincides with a narrow dispersive layer several electron inertial lengths (c/ω_pe) thick. Consequently, the nonlinear steepening is limited by wave dispersion. The DC electric field associated with the electron pressure gradient must also vary over these small scales, strongly influencing the efficiency of shocks as cosmic ray accelerators.

Chris Gurgiolo et al.

C. Gurgiolo¹, M. L. Goldstein², A. F. Viñas², A. N. Fazakerley³
¹Bitterroot Basic Research, Hamilton, Montana, USA
²Geospace Science Laboratory, Code 673, NASA Goddard Space Flight Center, Greenbelt, MD, USA
³Mullard Space Science Laboratory, University College London, Holmbury St. Mary Dorking, Surrey RH5 6NT, United Kingdom

Direct Observations of the Formation of the Solar Wind Halo from the Strahl

Observations of a gradual decrease the strahl density and subsequent build up of the halo density with distance from the sun suggests that, at least in part, the halo may be formed as a result of scattering of the strahl. In this presentation we will show direct observations of intense scattering of the strahl which gives rise to a proto-halo electron population which is neither field aligned nor is aligned with the nominal halo. This population eventually merges into, or becomes the halo. The scattering appears to occur in the absence of any strong monochromatic waves and appears to exist only in the solar wind, being rapidly quenched in the foreshock. The source of the scattering is not certain but one possibility which will be covered in a separate presentation is that the scattering is the result of highly oblique kinetic Alfvén waves.

Chris Gurgiolo et al.

C. Gurgiolo¹, M. L. Goldstein², W. H. Matthaeus³, A. F. Viñas², A. N. Fazakerley⁴
¹Bitterroot Basic Research, Hamilton, Montana, USA
²Geospace Science Laboratory, Code 673, NASA Goddard Space Flight Center, Greenbelt, MD, USA
³Bartol Research Foundation, University of Delaware, Newark, DE, USA
⁴Mullard Space Science Laboratory, University College London, Holmbury St. Mary Dorking, Surrey RH5 6NT, United Kingdom

Preliminary Results: Characteristics of the Taylor Microscale In the Solar Wind: Magnetic Field and Electron Velocity Measurements

In turbulent fluid flow, the Taylor microscale represents the scale length where viscous damping of eddies begins to give way to strong damping of turbulent fluctuations and general heating. The Taylor microscale can be estimated based on either the magnetic field or the electron fluid velocity from

λ_{T_α} = √ (‹α²›) ⁄ (‹(∇×α)²›)
where α is the fluctuating (mean free) component of either the electron fluid velocity or the magnetic field. This involves (for electrons) estimating the fluid velocity, removal of the mean, and estimation of the spatial derivatives of the fluctuation component to compute the curl. As will be shown spatial derivatives constructed from the mean free data exhibit a dependence on the spacecraft separation. This then precludes obtaining an absolute value for the Taylor microscale, but does allow for intercommunication of results estimated under periods of comparable spacecraft separation. Early results indicate that there is a linear relationship between the Taylor microscale and the solar wind velocity and that there is virtually no difference between the magnetic field and electron fluid velocity based Taylor microscale.

Melvin Goldstein et al.

M. L. Goldstein², C. Gurgiolo¹, A. F. Viñas², Fouad Sahraoui³, Haihong Che²
¹Bitterroot Basic Research, Hamilton, Montana, USA
²Geospace Science Laboratory, Code 673, NASA Goddard Space Flight Center, Greenbelt, MD, USA
³LPP Polytechnique, Paris, France

The Curious Relationship Between the Electron Strahl and the Dissipation of Electromagnetic Turbulence in the Solar Wind

Recently, the magnetic field data returned from the four Cluster spacecraft have been used to investigate how magnetofluid turbulence in the solar wind is dissipated. Although data from the flux gate magnetometer is limited to frequencies (in the spacecraft frame of reference) to about 10 Hz, the search coil data can be used up to several hundred Hz. The resulting power spectrum shows that a second inertial range is present between the proton and electron inertial length scales. (In the frame of the solar wind, the observed fluctuations actually have very low frequencies (< 1 Hz), but very small spatial scales.) There have been approximately 1000 intervals when the four spacecraft can be used together to determine directly the wavenumber spectrum of the fluctuations. Our interpretation is that these fluctuations are propagating nearly orthogonal to the local magnetic field. A preliminary analysis of the properties of these fluctuations suggests that their dissipation is controlled directly by the electron strahl in a manner that creates the observed temperature anisotropy of the strahl, which is T_⊥/T_|| ∼ 2.

Wai-Leong Teh et al.

W.-L. Teh, R. Nakamura, M. Fujimoto, E. A. Kronberg, P. W. Daly, and A. N. Fazakerley

Electron Dynamics in Reconnection Ion Diffusion Region

We report Cluster observations of electron dynamics within the ion diffusion region for magnetic reconnection in the Earth's magnetotail. The event provides us some insights into the electron dynamics in different locations of the diffusion region. With the 2-D reconstructed magnetic field map, we pinpoint the spacecraft locations within the diffusion region, which is ~9 ion inertial lengths away from the magnetic X-point.

Dominique Fontaine et al.

Synthesis of the work done on the particle percipitation and outflows above the polar cap arcs during periods of northward IMF

.

Lucile Turc et al.

Magnetic cloud structure before and after the bow shock crossing - First aproach

.

Chris Arridge et al.

C.S. Arridge, G.R. Lewis, A.J. Coates, M.K. Dougherty

Survey of anisotropic electron moments in Saturn's magnetosphere

The standard approach used to estimate the electron density and temperature of electrons in Saturn's magnetosphere from the Cassini Plasma Electron Spectrometer is to numerically integrate the observed fluxes from a single anode assuming the distribution is isotropic in the spacecraft frame (Lewis et al., 2008; Arridge et al., 2009). In this paper we remove the isotropic assumption and integrate fluxes organised by pitch angle to produce anisotropic moments, assuming the distribution function is gyrotropic in the spacecraft frame. Missing segments of the distribution function are filled using a number of different strategies.

There are numerous science drivers for such a study, for example to understand plasma transport, facilitate diffusive equilibrium calculations and understand pressure anisotropies in the ring current. In this paper we present our method for calculating n, T_|| and T_⊥ and discuss the limitations in our technique, paying particular attention to the validity of the isotropic assumption made by Rymer (2004), Lewis et al.(2008), Schippers et al. (2008), Arridge et al. (2009), and others. We then present a synoptic study of these moments from the entire Cassini mission at Saturn.

Matt Taylor et al.

Spatial distribution of rolled up Kelvin-Helmholtz vortices at Earth's dayside and flank magnetopause

The Kelvin Helmholtz Instability (KHI) can drive waves at the magnetopause. These waves can grow to form rolled up vortices and facilitate transfer of plasma into the magnetosphere. To investigate the persistence and frequency of such waves at the magnetopause we have carried out a survey of all Double Star 1 magnetopause crossings, using a combination of ion and magnetic field measurements. Using criteria originally used in a Geotail study made by Hasegawa et al., (2006), 17 candidate events were identified from the entire TC-1 mission (covering ~623 orbits where the magnetopause was sampled) a majority of which were on the dayside of the terminator. The relationship between density and shear velocity was then investigated, to identify the predicted signature of a rolled up vortex, as reported by Takagai et al., (2006) and implemented on Cluster and Geotail data in Hasegawa et al., (2006). All 17 events had some level of rolled up behavior, with 12 (71%) on the post noon, dusk flank. A clear dawn/dusk asymmetry is observed on the dayside with preferential growth on the dusk side. Combining the H2006 with the current study reduces the dawn-dusk asymmetry to 62%, suggesting the asymmetry is limited to dayside and a combination of local driving of the KHI and secondary processes work to bring a more symmetric distribution of vortices, anti-sunward of the terminator.

Jan Soucek et al.

Electron scale observations of solar wind magnetic holes and associated high frequency wave emissions

Magnetic holes, solitary large amplitude depressions in the interplanetary magnetic field, are commonly observed in the solar wind. Some of these magnetic structures are accompanied by bursts of electrostatic waves close to the electron plasma frequency localized inside the magnetic holes. We present an analysis of wave polarization from STEREO (S/WAVES instrument), detailed structure of the emission from the WBD instrument and measurements of the electron distributions inside the holes from PEACE. We demonstrate a clear correlation between the solar wind strahl and the waves and present the proposed mechanism of wave generation by strahl electrons. We also show partial results from the WBD/PEACE special operations campaign targeted at the holes which run in the spring of 2010.

Colin Forsyth et al.

Temporal evolution and electric potential structure of the auroral acceleration region from multi-spacecraft measurements

Bright aurorae are excited by the acceleration of electrons into the atmosphere in violation of ideal magnetohydrodynamics. Modelling studies predict that the accelerating electric potential consists of electric double layers at the boundaries of an acceleration region but observations suggest that particle acceleration occurs throughout this region. Using multi-spacecraft observations from Cluster we have examined the temporal variation and vertical structure of the AAR during two upward current region crossings on 14 December 2009. By comparing data from Cluster 3 and 4, which were on the same orbit track but separated by 192~s, we show that the potential drop below the altitude of these spacecraft increased at a rate of 5-10~V/s between the crossings, whereas the higher altitude potential drop remained constant. By quantitatively comparing the electron spectra measured by Cluster 1 and 3, which were separated in altitude, we determine when these spacecraft made magnetically conjugate observations and use these to investigate the distribution of the potential drop in the AAR. Our observations show that 17% of the total potential drop was, on average, between the spacecraft and that the spatially averaged electric field above the spacecraft was weaker than between them. We discuss these observations in the context of models of the structure of the AAR and previous observations.

Robert Fear et al.

Robert Fear, Steve Milan and Romain Maggiolo

High latitude observations of magnetotail plasma-sheet plasma in conjunction with a transpolar arc

Transpolar arcs (TPAs) are auroral features which extend into the polar cap from the night side of the main auroral oval. In their most developed form, TPAs and the main auroral oval resemble a Greek 'theta', hence their alternative name of theta auroras. Observations from low-altitude spacecraft have reported that the plasma distribution above a TPA is similar to that above the main auroral oval, indicating that TPAs exist on closed magnetic field lines embedded within the open polar cap, but very few simultaneous observations have been reported of TPAs and conjugate points further out in the magnetotail. A major candidate mechanism for TPA formation invokes the closure of lobe flux in a twisted magnetotail, where the closed flux is prevented from returning to the dayside as the twist causes the northern and southern hemisphere footprints of the closed field lines to straddle the midnight meridian. In this mechanism, closed flux builds up on the night side, so plasma similar to typical plasma sheet distributions should be observed at high latitudes embedded within the lobe. We present preliminary observations of three cases where the Cluster spacecraft observes plasma-sheet plasma embedded within the lobes, and at much higher latitudes than those at which the plasma sheet is usually observed. The plasma distributions are indicative of closed field lines, and the locations of the spacecraft map to a point on the TPA that is significantly poleward of the main auroral oval. These observations are consistent with TPAs being formed by the proposed reconnection/twisted magnetotail mechanism.

Robert Fear et al.

Robert Fear, Minna Palmroth and Steve Milan

Seasonal control of the location of flux transfer events signatures at the magnetopause

Most models of flux transfer event (FTE) formation produce pairs of structures, which in general move away from the subsolar region and give rise to signatures which can be observed in both the northern and southern hemispheres. However, the multiple reconnection line (X-line) model and some 3D reconnection mechanisms are capable of producing a single flux rope, allowing a different number of FTE signatures to be observed in the northern and southern hemispheres. Raeder [2006] reported the results of an MHD simulation where he studied the effect of the Earth's dipole tilt on reconnection at the dayside magnetopause for a southward IMF orientation; in his simulations, flux ropes were formed by the sequential formation of X-lines, and flux ropes moved preferentially towards the winter hemisphere. However, subsequent simulations (including one invoking truly three dimensional reconnection [Dorelli & Bhattacharjee, 2009]) have found no dependence upon dipole tilt. In this presentation, we examine the seasonal distribution of flux transfer event signatures observed by Cluster. We find that there is a seasonal dependence in this data set; once the seasonal bias is taken into account, we find that the IMF clock angle controls the location of FTE signatures.

Malcolm Dunlop et al.

M. W. Dunlop1^3,12, Q.-H Zhang², Y. Bogdanova⁴, Z. Pu⁵, H. Hasegawa⁶, K-H. Trattner⁹, M. Lockwood¹, M. G. G. T. Taylor⁷, J. Berchem⁸, D. Constantinescu¹⁰, B. Lavraud¹¹, J. Eastwood¹², H. Frey¹³, J Wild¹⁴, C. Shen³, J-K Shi³, M. Volwerk¹⁵, A. N. Fazakerley⁴, D. Sibeck¹⁶, P. Escoubet⁷
¹Space Science and Technology Department, RAL, Chilton, Didcot, Oxfordshire, OX11 0QX, UK
²SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai, China
³Center for Space Science and Applied Research, CAS, Beijing 100080, China
⁴Mullard Space Science Laboratory, University College London, Dorking, Surrey, RH5 6NT, UK
⁵School of Earth and Space Sciences, Peking University, Beijing 100871, China
⁶Department of Space Plasma Physics, ISAS/JAXA, Japan.
⁷ESA/ESTEC, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands
⁸IGPP, UCLA, 3877 Slichter Hall, Los Angeles, CA 90095-1567, USA.
⁹Lockheed Martin, Palo Alto, California, USA.
¹⁰Institut fur Geophysik und Meteorologie, TU-BS, D-38106 Braunschweig, Germany.
¹¹CESR, CNRS, 9 Ave. du Colonel Roche, 31028 Toulouse Cedex 4, France.
¹²The Blackett Laboratory, Imperial College London, London SW7 2AZ, UK.
¹³Space Sciences Lab., University of California, 7 Gauss Way, Berkeley, CA 94720-7450, USA.
¹⁴Space Plasma Environment and Radio Science group, Lancaster University, LA1 4WA, UK
¹⁵Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria
¹⁶Code 674, NASA/GSFC, Greenbelt, MD 20771 USA.

Magnetopause Reconnection Across Wide Local Time

The operation and extent of magnetic reconnection (MR) across the Earth's magnetopause has recently benefitted from an unprecedented growth in complexity of multi-point, in situ measurements, on the small and meso-scale, from Earth-bound space missions. Recent findings in active sites of MR have increased the theoretical understanding of the detailed structure within the ion diffusion region surrounding the magnetic X-line or null field, nevertheless, direct measurements of this small region in space are still relatively rare, owing to the time variable nature of the near-Earth space environment. During April to July 2007 a combination of 10 spacecraft (Cluster, THEMIS and TC-1) provided simultaneous monitoring of the dayside magnetopause across a wide range of local times. Here, we report direct evidence, taken from a conjunction of the THEMIS-A spacecraft and the Double Star, TC-1 spacecraft, of the X-line structure resulting from the operation of MR at two widely (~9 RE) separated locations along the expected sub-solar merging line (line of maximum current) on the Earths magnetopause. The near simultaneous conjunctions of all 10 spacecraft also identify an extended magnetic reconnection X-line, tilted in the low latitude, sub-solar region, which extends to (anti-parallel) locations on the dawn-side flank. The observed global pattern of FTE’s is consistent with the initially strong, but changing, IMF By conditions and supports the result that reconnection activity may occur simultaneously across the sub-solar and flank magnetopause, linked to the (large-scale) extended configuration of the merging line. The occurrence of MR is therefore consistent with a 'component' driven scenario and independent of guide field conditions.

Andrew Walsh et al.

A. P. Walsh¹, C. S. Arridge^1,2, A. Masters^1,2, A. N. Fazakerley¹, G. R. Lewis^1,2, A. J. Coates^1,2
¹Mullard Space Science Laboratory, University College London
²Centre for Planetary Sciences at UCL/Birkbeck

Characteristics of the Solar Wind Electron Distribution at 10AU

The electron distribution in the solar wind has 3 components a Maxwellian or thermal core, which is generally isotropic, a isotropic suprathermal 'halo' population existing at higher energy, which can be described by a kappa distribution, and the strahl - a beam of higher-still energy electrons that travels away from the Sun along the interplanetary magnetic field. The strahl can also be described by a kappa distribution. Current theories suggest the halo population is formed through pitch angle scattering of the strahl, so the presence or otherwise of each of these three populations can provide information about the evolution of the solar wind as it propagates through the heliosphere. To date there have been few observations of the solar wind electron distribution that include the higher energy, suprathermal, components made outside the orbit of Jupiter.

Here we use data from CAPS-ELS, flying on Cassini, to characterise the electron distribution that was measured upstream of Saturn while the Cassini was on approach to the planet. We find that the measured distribution does contain one or more suprathermal components measurable above instrument background levels, with a higher phase space density in the direction one would expect the strahl to be observed, although it cannot yet be confirmed that this distribution conforms to the core-halo-strahl structure observed closer to the Sun.

Andrew Walsh et al.

Andrew P Walsh¹, Colin Forsyth¹, Christopher John Owen¹, Andrew Neil Fazakerley¹, Iannis S Dandouras^2,3
¹MSSL, University College London, Dorking, United Kingdom.
²UPS-OMP, IRAP, Univeristy of Toulouse, Toulouse, France
³CNRS, IRAP, BP 44346, F-31028, Toulouse cedex 4, France

Dawn-Dusk Asymmetries in Average Magnetotail Pitch Angle Distributions

We present the results of a survey of Cluster PEACE and CIS-CODIF data taken in the 2001-2006 tail seasons, building on the work of Walsh et al. (GRL, 2011). We examine the average pitch angle distributions of protons and electrons in the magnetotail as a function of proton plasma beta, restricted to times when the magnetosphere was exposed to steady (on a 3 hour timescale) IMF conditions and focussing in particular on dawn-dusk asymmetries.

We confirm that, on average, the 2 component proton plasma sheet exists duskward of the noon-midnight meridian under steady northward IMF. An associated population of cold electrons is also observed. Dawnward of the noon-midnight meridian there are no significant fluxes of the cold component of protons and much reduced fluxes of the cold electron component, implying transport across the dusk magnetopause is the dominant formation mechanism of the two component plasma sheet for both protons and electrons.

Under southward IMF, dawn-dusk asymmetries in the protons are controlled by the Y component of the IMF. For the electrons higher fluxes of high energy, field-aligned, particles are observed at dusk than at dawn. This suggests a link to a duskward offset of the tail neutral line and the preferential observation of substorm-related tail signatures in the premidnight sector.

David Winningham et al.

Three Planet View of Electron Bow Shock Acceleration

Data from Cluster, Mars Express and Venus Express will be presented to clarify the exact nature of electron energization at planetary bow shocks. Evidence will be given that the main process is an increase in the parallel drift velocity of the electrons with minor bulk heating. The parallel drift velocity is close to the electron Alfven velocity.

Jeremy Mitchell et al.

Bowshock Heating and Magnetosheath Electron Communication

Solar wind electrons are heated as they cross the Earth's bowshock and enter the magnetosheath. The heating process is largely controlled by the electric potential difference across the shock. The motion of electrons in the magnetosheath provide a mechanism for communication between distant locations on the shock surface. This results in the local heating properties of the shock, such as the cross-shock potential, being influenced conditions at other locations on the shock surface. We present the results of a calculation determining the effects of such electron motion on these heating properties, and thereby predict the effects that electron communication has on the magnetosheath electron distributions. We predict that electron temperatures are remarkably constant throughout any given V-B plane in the magnetosheath, despite large variations in the total magnetosheath temperature predicted using the Rankine-Hugoniot jump conditions. We also find that the cross-shock potential is dependant upon the angle between the upstream magnetic field and the shock normal, tending to become very large for highly perpendicular shocks. We compare our results with electron data from PEACE and the THEMIS ESA instruments to show some qualitative agreement.

Roger Duthie et al.

BBFs & Dipolarisations : Substorm related phenomena of the terrestrial magnetotail

The question of how to model the terrestrial substorm has been a hot topic for around the last 50 years. There is still new evidence being presented and lively ongoing debate as to whether a substorm is triggered 'outside-in' or 'inside-out'. It is also still current to discuss how to place observable magnetotail phenomena within the model.

This 'in progress' study looks to address the significance of links between two of the phenomena observed in the terrestrial magnetotail - bursty bulk flows (BBFs) and dipolarisations. Consideration has been made for the apparent type of dipolarisation - as distinction does lie in whether a transient or persistent increase in the elevation angle of the magnetic field occurs, as well as whether the field seems to be in an elevated state prior to any enhancement. Also, condsideration has been given to the substorm phase at the time of the detection of BBFs and dipolarisations.

This study uses all four Cluster spacecraft to identify BBFs and both Double Star spacecraft to detect dipolarisations. Use is made of PEACE on all four spacecraft to generate electron plasma beta values to identify plasma sheet - this being the region where BBFs are detectable. Also, ExB drift velocity data derived from the measurements from field instruments (FGM & EFW) on all four spacecraft are used to gauge bulk transport of plasma, in concert with particle instrument data (CIS & PEACE). Substorm phases are identified using the AL index, though the use of the SuperMAG SML index is considered.

Preliminary results suggest that there is little evidence that BBFs observed in the near-tail are a cause for the detected earthward dipolarisation events.

Branislav Mihaljčić et al.

Cluster Penetrating Radiation Studies

The Cluster PEACE sensors can be turned on during the radiation belt crossings. However data can be contaminated by high count rates due to penetrating radiation. The question is, can such data be corrected to recover the true plasma counts measured by the PEACE sensors. Further studies aim to reveal if penetrating radiation affects all the anodes equally to aid in the calibraton process and production of scientifcally relevant support data.

Roger Duthie et al.

Cross-Calibration & Hybridisation of Data from Cluster Spacecraft to Probe the Magnetotail Plasma Sheet

Use can be made of all four Cluster spacecraft to detect what are known as burst bulk flows (BBFs) in the central plasma sheet of the terrestrial magnetotail. These flows are fast (of order 100s km/s) and perpendicular to the magnetic-field. They are structured into intermittent flow bursts with duration of order ~1 minute and a complete BBF event is detectable at one spacecraft for ~10 minutes. It has been seen that the detection rate of this type of phenomenon increases with the addition of extra Cluster spacecraft [Cao et al., JGR, 2006].

The Cluster spacecraft were designed and built to carry the same compliment of instrumentation on-board - to facilitate uniform observation at multiple points in space. However, in practice, the compliment of instruments is not the same on each spacecraft due to malfunctions in hardware. Fortunately, there are instruments that measure the electric and magnetic fields to high time resolutions operating well on all four spacecraft, this means the ExB drift velocity can be derived. Unfortunately, electric field data are not available at all times when BBFs could be detected; this necessitates use of velocity measurements derived from particle data, either electrons or ions, where the operability of instruments permits it.

After some modification to some of the data, a set of 'hybrid' perpendicular velocity data can be constructed from field and particle measurements. These can then be used to observe plasma flows from all four Cluster spacecraft in a uniform way.

George Parks et al.

G. K. Parks, J. Hong, E. S. Lee, M. McCarthy, I. Dandouras.

Parallel electric field and solar wind

The current picture of the solar wind (SW) flow is driven by pressure gradient that pushes the coronal atmosphere outward. A unique feature of the SW is that it consists of beams in the velocity space, which can be represented as a Maxwellian distribution in a flowing fluid. However, there are numerous observations that indicate the beams are not in thermal equilibrium. A possible interpretation of these SW beams is that they are accelerated by an electric field parallel to the magnetic field direction, similar to what is occurring over the aurora. We have started to examine this idea and this talk will report preliminary results of our studies including what we are learning from simulation models.

David Winningham et al.

Statistical study of the NTC plasmaspheric patches: a direct link between wave observation in the inner magnetosphere and magnetic activity

SDDAS is updating the way a scientist looks at data. We are trying to develop a generic system that allows a scientist to look at data, regardless of format, regardless of location. We want this system to work as seamlessly with all data types and servers as easily as it works with IDFS data. However, with IDFS data, we have extra metadata that we can take advantage of, so we are improving the software with that format as well.

Sandrine Grimald et al.

tbc

Variations in the solar wind are responsible of reconfiguration of the whole magnetosphere. The plasmapause is located in the inner magnetosphere and a direct link between its characteristics and the magnetic activity has been shown. Non-thermal continuum (NTC) radiation is believed to be emitted at the plasmapause and near the magnetic equator. The changes of the plasmapause due to solar wind variations may be reflected in the wave signature.

In a recent study, a particular type of NTC radiation, referred to as NTC plasmaspheric patch, has been identified. It has been shown that this spectral signature only exists close to its source region. The Cluster perigee is located at 4 RE, in the plasmapause region. Using three years of Cluster data we perform a statistical study about the NTC plasmaspheric patches in correlation with the evolution of the magnetic activity. Our results show that NTC plasmaspheric patches observation is the signature of an increasing of the magnetic activity. It is linked with a compression of the plasmapause, and an increasing of the magnetic indices.

Michael Balikhin et al.

Magnetic holes in the vicinity of dipolarisation fronts: Mirror or Tearing structures?

Magnetic holes filled with isotropic energetic electrons (up to a few 10⁵ eV ) have been observed by THEMIS in the vicinity of dipolarisation fronts. These structures can partially contribute to the initial seed population of energetic electrons within the magnetopshere, therefore finding their nature is important for understanding of the population of high energy electrons within the magnetosphere. Previously these structures have been interpreted as the result of the mirror instability due to the similarity in their appearance with mirror dips observed in the terrestrial magnetosheath and solar wind. The THEMIS data shown here prove that the measured properties of these waves contradict to their interpretation as mirror waves. In the present study it is shown that that these waves have no significant effects on ion the population as would be expected for mirror wave structures. However, they do have a pronounced effect on the high energy electron population.The evolution of the high energy electron population within these structures is investigated. It is then argued that the tearing instability can be responsible for their generation.

Michael Balikhin et al.

The analysis of electron fluxes at geosynchronous orbit

The Methodology based on the Error Reduction Ratio (ERR) determines the causal relationship between the input and output for a wide class of nonlinear systems. In the present study, this ability of the ERR has been used to identify the most important solar wind parameters, which control the fluxes of the energetic electrons at geosynchronous orbit. The results show that for lower energies, the fluxes are indeed controlled by the solar wind velocity, as it was assumed before. For the lowest energy range studied here (24.1 keV), the current days solar wind velocity is the most important control parameter for the current days electron flux. As the energy increases, the previous days solar wind velocity becomes the most important factor. For the higher energy electrons (around 1 MeV), the solar wind velocity registered two days in the past is the most important controlling parameter for the current days electron flux. Such a dependence can be explained by either local acceleration processes due to the interaction with plasma waves or by radial diffusion if lower energy electrons possess higher mobility. Analytical solutions of local waves based energy diffusion shows that the increase of electron fluxes should me much slower than observed in data. It is concluded that it is the radial diffusion that plays key role in the increase of fluxes at GEO for the energy range up to 1 MeV. In the case of even higher energies (2.0 MeV), the solar wind density replaces the velocity as the key control parameter. Such a dependence upon density does not have a straight-forward explanation in the frame of the presently accepted theories for diffusive acceleration.

Sandrine Grimald et al.

Study of the applicability of the curlometer technique with the four Cluster spacecraft in regions close to Earth

Knowledge of the inner magnetospheric current system (intensity, boundaries, evolution) is one of the key elements for the understanding of the whole magnetospheric current system. In particular, the calculation of the current density and the study of the changes in the ring current is an active field of research as it is a good proxy for the magnetic activity. The curlometer technique allows the current density to be calculated from the magnetic field measured at four different positions inside a given current sheet using the Maxwell-Ampere's law. In 2009 the CLUSTER perigee pass was located at about 2 RE allowing a study of the ring current deep inside the inner magnetosphere, where the pressure gradient is expected to invert direction. In this paper, we use the curlometer in such an orbit. As the method has never been used so deep inside the inner magnetosphere, this study is a test of the curlometer in a part of the magnetosphere where the magnetic field is very high (about 4000 nT) and changes over small distances (B = 1 nT in 1000 km). To do so, the curlometer has been applied to calculate the current density from measured and modelled magnetic fields and for different sizes of the tetrahedron. The results show that the current density cannot be calculated using the curlometer technique at low altitude perigee passes, but that the method may be accurate in a [3 RE;5 RE] or a [6 RE;8.3 RE] L-shell range. It also demonstrates that the parameters used to estimate the accuracy of the method are necessary but not sufficient conditions.

By Andrew Fazakerley
Last updated on by Branislav Mihaljčić