ESA Science & Technology - Cluster Guest Investigator Operations, 2015-2016

Following a review in Summer/Autumn 2014 by the Cluster Science Operations Working Group, and by a Peer Review Committee with members from the Solar System and Exploration Working Group, eight GI proposals were selected. These are detailed below:
 

Nominally, outside eclipses, data is acquired all along the Cluster orbit as follows: 52.5 hours Normal Mode (NM) and 1.5 hours Burst Mode (BM). During the period of the GI operation implementation, the Cluster Science Operations Working Group defined a new style of spacecraft operations to enhance the amount of burst mode data per orbit, which benefitted the science objectives of the GI activities and other Cluster science targets. This was made possible by imposing a period of no data taking during another part of the orbit, to offset the increased load of the enhanced BM. The NM data rate is around 17 kbps (kbps: kilo bits per second) and the BM data rate is 105 kbps. So, for every extra hour of BM data, we impose 8 hours of no data taking on the C1, C2 and C3 spacecraft while C4 continues to acquire data.

Information on specific operations is detailed below (once in the planning), including periods of enhanced/extended BM periods, in the order in which they were or will be implemented.

The proprietary data period for the GI will be at least 6 months after measurements were made. During this period data access is limited to the GIs and the PI teams. After at most 9 months the PI teams will deliver the data to the Cluster Science Archive (CSA) where it will be publicly accessible. This will enable the PI teams to keep to their agreed CSA delivery schedule and provide GIs time to carry out their analysis.

Should you wish to analyse Cluster data from during the GI periods, you are strongly encouraged to contact the project scientist team at ESTEC, via Philippe Escoubet (email: philippe.escoubetesa.int), who will liaise with the GI teams.

Guest Investigator: Olga Alexandrova

Proposal title: Study of the dissipation range of solar wind turbulence

Abstract

Turbulence is a universal and omnipresent multi-scale process in plasmas. Despite many observations of the turbulence in space plasmas, a number of key issues are still poorly understood; one of them is the collisionless dissipation. Recent Cluster observations in the solar wind show that the dissipation of the electromagnetic turbulent cascade probably happens at electron scales. This is well supported by recent kinetic simulations and theory. Two dissipation mechanisms at kinetic scales have been proposed: reconnection within thin current sheets and resonant damping of fluctuations on electrons. We propose to study these different scenarios using magnetic and electric field fluctuations and particles data at the highest possible rate in time and with spatial measurements at electron scales. The results expected from this study will improve our understanding of the dissipation in space plasma turbulence and provide a background for future missions.

Implementation

The requirement is to have two spacecraft (C3-C4) collecting data in the solar wind and magnetosheath, at a few kilometres from each other and in addition to do measurements when this distance varies from a few kilometres to around 1000 km. The other spacecraft are a few 1000s kilometres upstream of C3 and C4. We will use orbits when the spacecraft are in eclipse at perigee since there is enough time to dump solar wind data to the ground before switching off the spacecraft for the eclipse.

The periods where burst mode 1 (BM1) will be used are the following (SW indicates solar wind and MS magnetosheath):

C3-C4=6-7 km (3h BM1)

C3-C4=7 -> 1000 km (1h BM1)

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Guest Investigator: David Burgess

Proposal title: Ion pickup coupling in the solar wind associated with thruster operations

Abstract

Thruster operations are vital for maintaining spacecraft orbit and attitude. Chemical thrusters, as used by Cluster, produce a plume of neutral molecules which in turn produce ions via photo- and impact ionization. The new-born ions represent the injection of a new plasma constituent which mass loads the solar wind flow. Furthermore they have a high velocity in the solar wind frame, due to the relative velocity of spacecraft and solar wind, which acts as a free energy source for coupling between the solar wind and the injected ions. The effects of thruster operations on the ambient plasma are important for mission planning where the science aims are to measure the ambient plasma. They are also interesting in themselves, viewed as the observational results of an active plasma experiment. We propose a programme of Cluster science operations during thruster operations to make comparisons with simulations being carried out to study the large scale effects of interaction between the ambient solar wind and ions injected from the thruster plume. Special simulations will be run specific to the Cluster configurations and events in order to validate the simulation methods. The simulations will have possible implications for mission planning for future missions such as Solar Orbiter and Solar Probe Plus, where the effects of thruster firings on the ambient plasma might have to be taken into account.

Implementation

The goal of this investigation is to collect electric and magnetic field data at spin resolution during the thrusters firing on one spacecraft. We will use three thrusters firing intervals where one is a long firing interval of 17 min (Cluster 1) and the two others are 7-8 s long (Cluster 3). We will use burst mode 2 (BM2) for 1 h during these intervals since there is a special interest from the WBD team to acquire data while other instruments (WEC and FGM) collect normal mode equivalent data.

The planned periods are:

Cluster 3 thrusters firing: 09/03/2015 09:14:41-09:14:49
Cluster 1, Cluster 3 and Cluster 4 with WEC + FGM on in BM2: 09/03/2015 09:10-10:10

Cluster 1 thrusters firing: 17/03/2015 14:04-14:22
Cluster 1, Cluster 3 and Cluster 4 with WEC + FGM on in BM2: 17/03/2015 13:59 -14:59

Cluster 3 thrusters firing: 25/03/2015 05:28:03-05:28:11
Cluster 1, Cluster 3 and Cluster 4 with WEC + FGM on in BM2: 25/03/2015 05:23-06:23

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Guest Investigator: M. Dunlop

Proposal title: Coordination of Cluster/Swarm for FACs

Abstract

This proposal is designed to establish special operations between Cluster and Swarm, in order to take best advantage of conjunctions between the two missions. A special configuration which optimized the coverage of the ring current, sampled in situ by Cluster, was established for the beginning of Swarm science operations in 2014, when all three Swarm orbits will be closely aligned. It is hoped and anticipated that the optimum constellations of Cluster in the ring current (RC) will be maintained into 2015, but also secondary science targets (for example, at high-latitude conjunctions) are possible during closely conjugate periods between Cluster and Swarm, and here we seek to focus on these for a special Cluster operational phase during 2015. The exact periods and phasing will not actually be known in detail until the end of the Swarm commissioning phase and final completion of manoeuvres. However, it is known that conjunctions will occur at intervals during the Cluster phase. The LT drifts of the Swarm orbital planes are between 100 deg (spacecraft B) and 130 deg (pair A/C) per year, so that Cluster and Swarm will come into LT alignment about every ~1.3 years, and will remain closely aligned for a month or so; a suitable target period for special GI operations. It is desirable to establish this coordination in 2015 when the Swarm A,C and B are not too far apart in LT. In addition to this consideration, it is likely that constellations set up for the best ring current coverage will also provide good sampling of the high latitude region either side of perigee where field aligned currents (FAC) and electron flux can be targeted for magnetically conjugate times. The best Cluster orientations for nightside FACs (e.g. SCW) and dayside FACs (e.g. Cusp) occur around June and December 2015. We intend to target the best regions (and hence periods) when the final orbits of Swarm are known, but anticipate this will be during either June or December each year.

Implementation

The spacecraft were configured to make the best measurements of the ring current in June 2015. The spacecraft have a separation around 1500 km with C2 closer to the Earth, C3/C4 further away and C1 in between, at perigee around the equatorial plane.

Normal mode 1 (NM1) data has been acquired around perigee during the month of June 2015.

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Guest Investigator: Yulia V. Bogdanova

Proposal title: Mid-altitude cusp properties, dynamics, small-scale plasma structure and ion outflow: simultaneous Cluster measurements at different MLT sectors

Abstract

The magnetospheric cusp is a key region in the solar wind-magnetosphere-ionosphere coupling and the investigation of the cusp region has been one of the aims of the Cluster mission. Recent observations reveal that the cusp is a dynamic and complex region governed by changes in external conditions, with multi-scale physical processes co-existing inside the cusp and cleft, including plasma injections from the reconnection site(s), small-scale electron beams and filamentary field-aligned currents, different mode wave excitation corresponding to plasma injections, local ion heating and outflow. The observations inside the cusp also have been successfully used in the past for the estimation of the geometry and properties of the reconnection at the magnetopause. In 2015/2016 Cluster is expected to cross the mid-altitude northern cusp region along the azimuthal direction, from the dusk to dawn, thus providing a unique opportunity to investigate azimuthal structure of the cusp and cleft regions. To facilitate this study, we propose to shift Cluster spacecraft along the orbit in a way that SC1 and SC2, and SC2 and SC3/4 will be separated by 1 h in MLT and can simultaneously monitor plasma processes at different parts of the cusp/cleft. The goals of this GI proposal are twofold: (i) investigation of the large scale cusp dynamics and morphology at different MLT sectors; cusp azimuthal extension and plasma properties corresponding to the different reconnection geometries at the magnetopause, and estimation of the location and properties of the reconnection site(s) responsible for the cusp injections at different MLT sectors; (ii) Investigation of the local ionospheric ion heating and outflow as observed along the heating wall at different MLT sectors and small-scale plasma processes related to this outflow, including characterisation of the electron beams, filamentary field-aligned currents, and excitation of the plasma waves responsible for the ion heating. We plan to use data from the following Cluster instruments: PEACE, CIS/CODIF on SC4, FGM, EFW, STAFF, and WHISPER. To complement Cluster data analysis, we plan to use EISCAT data for monitoring the ionosphere and MHD modelling for estimation of the large-scale reconnection geometry corresponding to Cluster observations at different MLT sectors.

Implementation

The selected intervals are:

30/10/2015  10:45-13:45 UT  -  BM1
01/11/2015  15:45-19:45 UT  -  NM1
08/11/2015  11:30-14:30 UT  -  BM1
10/11/2015  16:30-20:30 UT  -  NM1
19/11/2015  17:00-21:00 UT  -  NM1
26/11/2015  13:00-16:00 UT  -  BM1
28/11/2015  17:45-21:45 UT  -  NM1
05/12/2015  13:00-17:00 UT  -  BM1
14/12/2015  13:30-17:30 UT  -  NM1
23/12/2015  13:45-17:45 UT  -  BM1

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Guest Investigator: Yuri Khotyaintsev

Proposal title: Multi-spacecraft Investigation of Electron Scales at Bow Shock

Abstract

Shocks are ubiquitous in the Universe, producing some of the most spectacular, visually striking, and energetic phenomena. Astrophysical shock waves can be generated by supernovae, stellar winds, and the rapid motion of objects such as neutron stars. There are a wide variety of shock waves in the heliosphere driven by transients, fast streams, and obstacles (e.g., magnetized or unmagnetized planets) in the solar wind. Shock waves are believed to be one of the most efficient particle accelerators in astrophysical plasmas. The majority of the plasmas in the Solar System are classified as collisionless. Meaning, their associated energy dissipation cannot rely upon particle collisions. The dissipation occurs on kinetic scales (e.g., gyroradius and/or inertial scale) of different particle species, electrons and ions. Such scales are not accessible to remote observations and can only be studied in situ. Observations at ion scales have been well addressed by Cluster. However, these show that shocks often have scales as small as electron scales, and at these scales there are presently no multi-spacecraft measurements available. This project will require at least 2 of the Cluster spacecraft to move within a few km separation while in burst mode operation (BM1) for expected bow-shock locations. We would also like to increase the amount of EFW internal burst data taken for high-resolution E & B measurements by having more frequent BM3 dumps. We prefer all the data to be distributed via CAA/CSA.

Implementation

10 orbits with 7h BM1 on C3-C4 and 1h BM1 on C1-C2 centred on the bow shock were selected during January 2016. EFW internal memory was dumped through BM1 every hour using WEC internal commands.

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Guest Investigator: Primoz Kajdic

Proposal title: Magnetic reconnection in the solar wind: search for small-scale events

Abstract

The most commonly studied signatures of magnetic field reconnection in the un- perturbed solar wind (SW) are the so called reconnection exhausts (e.g. Gosling, 2005; Davis et al., 2006; Lavraud et al., 2009; Gosling, 2012). These have been observed in the magnetic field and plasma data of several missions (ACE, Wind, Stereo, Cluster, etc.). When a spacecraft crosses a reconnection exhaust it observes a rotation of the interplanetary magnetic field (IMF). This rotation occurs in two steps, at two distinct rotational discontinuities (RD) or Alfvén waves that bound the event and represent its edges. Magnetic field configuration between the edges is intermediate to those bounding the reconnection exhaust on each side. The two Alfvén waves propagate parallel (antiparallel) with respect to the B-field and hence produce anticorrelated (correlated) changes in SW bulk velocity and the IMF. The measured SW speed inside the reconnection exhaust is increased with respect to the surrounding values if the spacecraft crosses the event anti-sunwards of the reconnection X-line while it appears diminished on the sunward side.

Here we propose to use high-time-resolution magnetic field and plasma data of the four Cluster spacecraft in order to search for 1) small scale reconnection events with durations of less than three seconds and 2) the regions in which the magnetic reconnection actually takes place.

Implementation

10 orbits with 3h BM1 in the solar wind were selected in February-March 2016. C3 and C4 were separated by 100 km while C2 was 10 000 km in front of them and C1 10 000 km behind them.

2016-02-01  09:30-12:30  -  BM1
2016-02-03  15:50-18:50  -  BM1
2016-02-05  21:10-00:10  -  BM1
2016-02-10  06:10-09:10  -  BM1
2016-03-08  18:50-21:50  -  BM1
2016-03-11  02:30-05:30  -  BM1
2016-03-13  08:30-11:30  -  BM1
2016-03-15  14:30-17:30  -  BM1
2016-03-17  20:30-23:30  -  BM1
2016-03-20  02:10-05:10  -  BM1
 

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Guest Investigator: Xochitl Blanco-Cano

Proposal title: Upstream transients and their influence on the bow shock and magnetosheath

Abstract

The solar wind interaction with the terrestrial environment begins well ahead of the magnetopause when the solar wind encounters the foreshock, bow shock and magnetosheath. In these regions a variety of waves and magnetic structures exist and modify solar wind properties. The foreshock is permeated by a variety of ultra-low frequency (ULF) waves and magnetic transient structures such as shocklets, SLAMs, and cavitons (Blanco-Cano et al., 2009; Kajdic et al., 2013). These structures can be very compressive and are generated by the solar wind interaction with backstreaming particles plus non-linear processes. In the case of cavitons, it is the interaction between two types of waves which leads to the formation of large depressions in density (n) and magnetic field magnitude (B) bounded by enhanced compressive shoulders in n and B.

The purpose of this project is to use the Cluster multi-spacecraft, high time resolution capabilities to study foreshock transients, their evolution and their influence on the bow shock and magnetosheath structures. These transients can contribute to bow shock rippling and part of the research focus on determining quasi-parallel shock rippling scales.

Implementation

10 orbits with the spacecraft in NM1 in the solar wind and at the quasi-parallel shock were selected in March-April 2016. NM3 was used on C1 and 1h of BM1 at the inbound bow shock. The spacecraft followed each other with around 1 R_E separation distance along their orbit.

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Guest Investigator: Claire Foullon

Proposal title: Magnetopause boundary layer: evolution of plasma and turbulent characteristics along the flank - repeats

Abstract

The magnetopause and its adjacent boundary layers have been a key science target for many satellite missions. They have been sampled, at the same time, either locally by a maximum of 4 to 5 closely spaced spacecraft (from the Cluster constellation and the Double Star TC-1 satellite) or on larger scales by missions such as Geotail, Cluster and THEMIS. Unfortunately none of the spacecraft configurations has so far permitted to track the "evolution" of perturbations in their main direction of propagation. The study of the evolution of plasma perturbations, such as Kelvin-Helmholtz (KH) waves or Flux Transfer Events (FTEs), together with the (associated or not) generation of Kinetic Alfvén Waves (KAWs) and the turbulence developing at the flank magnetopause boundary layer, is important for our understanding of the mechanisms that mediate solar wind plasma entry into the magnetosphere, i.e. magnetic reconnection and diffusive processes. The Cluster Guest Investigator (GI) proposal implemented in November 2012 on the Dusk flank targeted inter-spacecraft separations of about 1 R_E necessary to relate disturbances and deduce their evolution. It resulted in separations of up to 36 000 km across the constellation at the magnetopause and was the largest separation ever for the Cluster mission. One of the events studied allows us to study changes to the magnetopause boundary layer properties during the passage of an Interplanetary Coronal Mass Ejection (ICME). We would like to repeat the November 2012 GI operation on the Dawn flank, to increase the probability to have phenomena of interest travelling roughly parallel to the alignment, and to provide a study of asymmetries between the two flanks.

Implementation

10 orbits with around 10h NM1 + 5h of BM1 + 10h NM1 centred on the dawn flank of the magnetopause have been selected in June 2016. The spacecraft follow each other with around 1 R_E separation distance along their orbit.

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For further details, please contact:

Philippe Escoubet, Cluster Project Scientist

Email: Philippe.Escoubetesa.int