EFW meeting in Uppsala, September 2001

Start: 13:00, Thursday, September 6
End: 15:00, Friday, September 7

Minutes by Andris Vaivads, Mats Andre, Anders Eriksson

Introduction (Mats André)
EFW data quality (A. Eriksson, H. Laakso, P.-A. Lindqvist, A. Pedersen)
Interference (Mats André, Anders Eriksson, Harri Laakso, Per-Arne Lindqvist)
Cluster Science Data System:CSDS (Per-Arne Lindqvist)
---------- EFW E-field compared with other instruments (M. André, H. Laakso)
--------------------VxB using CIS (ion drift observations) and FGM (B-field)
--------------------VxB using FGM and assuming a corrotating plasmsphere
----------Spacecraft potential and density: (A. Pedersen, H. Laakso, A. Masson)
Operations (Anders Eriksson)
----------Most used real time sampling
----------Bias settings
----------Bias sweeps
----------Problem with the 10 Hz filter on probe 3, s/c2 (M. André, P.-A. Lindqvist)
---------- EFW internal burst (Mats André, Anders Eriksson)
-------------------- Usage up to now:
-------------------- Plans for the near future:
---------- Special orbits (Mats André)
Future meetings
Science presentations
Software packages (Anders Eriksson, Tobias Eriksson, Harri Laakso)
EFW on the web
Upcoming EFW meetings
Presentations in electronic form


Anita Aikio anita.aikio@oulu.fi
Mats André mats.andre@irfu.se
Rico Behlke rico@irfu.se
Jan Blecki jblecki@cbk.waw.pl
Lars Blomberg blomberg@plasma.kth.se
Rolf Boström rb@irfu.se
Stephan Buchert stephan.buchert@irfu.se
Tobia Carozzi tc@irfu.se
Paul Eglitis Paul.Eglitis@irfu.se
Anders Eriksson Anders.Eriksson@irfu.se
Tobias Eriksson tobbe@irfu.se
Carl-Gunne Fälthammar falthammar@plasma.kth.se
Georg Gustafsson gg@irfu.se
Igor Ivonine ivonin@irfu.se
Yuri Khotyaintsev yuri@irfu.se
Harri Laakso hlaakso@so.estec.esa.nl
Per-Arne Lindqvist lindqvist@plasma.kth.se
Elizabeth Lucek e.lucek@ic.ac.uk
Björn Lybekk bjorn.lybekk@fys.uio.no
Göran Marklund marklund@plasma.kth.se
Arnaud Masson Arnaud.Masson@esa.int
Kalevi Mursula kalevi.mursula@oulu.fi
Anssi Mälkki anssi.malkki@fmi.fi
Annika Olsson ao@irfu.se
Hermann Opgenoorth Hermann.Opgenoorth@irfu.se
Arne Pedersen arne.pedersen@fys.uio.no
Tuija Pulkkinen tuija.pulkkinen@fmi.fi
Kristof Stasiewicz ks@irfu.se
Gabriella Stenberg stenberg@space.umu.se
David Sundqvist davids@rymdfysik.uu.se
Pekka Tanskanen pekka.tanskanen@oulu.fi
Anders Tjulin Anders.Tjulin@irfu.se
Jan-Erik Wahlund jwe@irfu.se
Andris Vaivads andris@irfu.se
Lennart Åhlen ala@irfu.se
Simon Walker simon.walker@shef.ac.uk

Introduction (Mats André)

Recent EFW observations of the magnetopause can be found on the ESA web page http://www.esa.int (Cluster mission). This presentation has been selected by the Cluster project scientist and ESA PR representatives and is intended for the press and the general public.

The overall status of the Cluster mission is good. The satellite separation will be 100 km during the next dayside/cusp period of operations. The instruments are operated according to a Master Science plan, available at JSOC http://jsoc1.bnsc.rl.ac.uk.

The status of the EFW instrument is good. The only hardware problem is that the 10Hz filter on probe 3, sc/2, is not operational since late July. Continuous fine tuning will always be necessary (internal bursts, bias currents etc). Interference from other instrument is discussed below.

For further general information, see the EFW web page http://cluster.irfu.se/.

EFW data quality (A. Eriksson, H. Laakso, P.-A. Lindqvist, A. Pedersen)

Summary: EFW delivers high-quality data down to 0.1 mV/m, though careful analysis and cross-checking is always needed. The frequency range of the spin and its first harmonics (between .25 and about 2 Hz), is particularly tricky, where many effects combine: Outside the spin frequency range, EFW data are more straightforward to analyze, the main exceptions being the spurious sunward electric field and some obvious interference lines in spectra above 10 Hz, and interference from other instruments (see below).

An obvious but minor effect (if using V_ps to estimate the plasma density) is the 1 Hz modulation of the V_ps sometimes seen for all four probes (in phase) on one satellite. An interpretation is based on the fact that the boom area is 10% of the spacecraft area and as a result the total photoelectron emission is modulated with the satellite spin. The highest V_ps value is obtained when the boom angle is 45deg with respect to the sun. The effect appears mainly in low density environment (For example, 2001-07-21 0510-0519 UT).
(Sometimes modulations of EFW data are caused also by the stiff magnetometer booms, causing 0.5 Hz modulations)

Interference (Mats André, Anders Eriksson, Harri Laakso, Per-Arne Lindqvist)


The quasistatic E field around each satellite is significantly influenced by the ion emitting instrument ASPOC. When ASPOC is on, the E-field seen by EFW is not the natural magnetospheric field of interest. Both the sunward and duskward components of E can change when ASPOC is turned on (for an example, see 2001-01-16,16-17 UT). (A report on ASPOC/EFW interference is available, ask Mats André for a copy). Presently this is solved by a 50/50 timesharing, so that ASPOC is on 50% of the time as compared to plans before launch. Per-Arne Lindqvist is performing a statistical study of ASPOC interference. The effect of ASPOC is not always large. The dependence on parameters such as electric field magnitude (a perturbation of a small field may be regarded as a small effect, but still gives a large relative error) and EFW bias current (smaller bias current may decrease the interference) is of interest.


Particularly in burst mode telemetry (450 samples/s), there is a clear (and expected) interference from active sounding by WHISPER. The signals last a few seconds, typically every 28 or 104 s. The interference can easily be seen both in the EFW time series and as multiple bands in EFW spectrograms. There might be less interference with smaller EFW bias current. The effect can sometimes but not always be seen also in normal mode sampling (25 samples/s). There is also a decrease in the V_ps (the probe-to-satellite potential, often referred to as the negative of the spacecraft potential) during WHISPER operations in tenuous plasmas (For example, 2001-02-02, 0807-0812 UT)

During the validation of data for Prime Parameters, time periods with bad data are sometimes removed (Per-Arne Lindqvist). If you cannot find Prime Parameter (PP) data, there is probably a problem with the data. However, time periods with ASPOC ON are not removed from PP, and these periods may have significant interference.

Cluster Science Data System:CSDS (Per-Arne Lindqvist)

EFW data from 1 January 2001 to 30 June 2001 is online at CSDS.
VxB is subtracted.
CSDS includes: V_ps, E_dusk, sigma (estimate of wave activity) and power in two frequency bands (0.3-10Hz, 10-180Hz).

Satellite spin, 4 s, sine wave fit of E -> Prime Parameters PP.
One minute averages -> Summary parameters SP.
The EFF E-field obtained with 4 s resolution (in house keeping telemetry) is not included in CSDS.

For more information see http://www.plasma.kth.se/cdms/ and http://www.cluster.rl.ac.uk/cdms_dblist.htm

Several tens of MB per month are downloaded from SCDS.

Data are screened manually (Per-Arne Lindqvist):

The time lag caused by data screening and validation is about one month. All EFW data will be reprocessed this autumn. Improvements will include:


EFW E-field compared with other instruments (M. André, H. Laakso)


Good agreement for some selected events (For example 2001.02.07, 00.00-02.00 UT see Fig 2 of the ASPOC interference report, c.f. ASPOC interference section above). Examples with good agreement are mainly obtained when the common axis is close to the dusk direction. The EFW and EDI teams will compare more events in detail during the next few weeks.

VxB using CIS (ion drift observations) and FGM (B-field)

Examples of very reasonable agreement can also be found in the ASPOC interference report.

VxB using FGM and assuming a corrotating plasmsphere

An example by Laakso (2001-02-28 0925-1025 UT, see Figure 1 of the ASPOC interference report) shows very reasonable agreement. (In this figure a small offset was introduced in the duskward EFW E-field component.)

Spacecraft potential and density: (A. Pedersen, H. Laakso, A. Masson)

Comparisons have been made between V_ps (estimate of the negative of the satellite potential, which is sensitive to the plasma density) and densities obtained by WHISPER (via the plasma frequency) and by CIS. The plot below is provided by Laakso.

The difference between Cluster and Polar in dependence of density versus V-sp was discussed. Additional methods of determining the density, such as cutoffs in wave spectra were mentioned.

Arnaud Masson briefly discussed an automatic procedure to fit Whisper and Vps (sse also his scientific presentation).

Operations (Anders Eriksson)


Most used real time sampling

Bias settings

Bias sweeps

David Sundkvist in Uppsala is working on sweeps, particularly the varying photoemission characteristics.

Problem with the 10 Hz filter on probe 3, s/c2 (M. André, P.-A. Lindqvist)

Since late in July 2001, the 10Hz filter on p3 of sc2 is not functioning properly.

In principle several options are available for future operations in NM (25 samples/s), including:
1) 180 Hz filter on all probes all spacecraft (gives identical s/c).
2) 180 Hz filter on s/c 2, while other s/c use 10 Hz filters (closest possible to original design, gives filters identical to B-field observations by STAFF on three s/c).
3) 180Hz filter probes 3 and 4 of s/c2, the rest use 10Hz filter (this would make despin unreliable, would require changes in the flight software on s/c 2 etc). After a discussion it was decided that this option was not realistic.

During the last week of July, data from s/c 2 may be unreliable due to the probe problem. During August 2001, option 1 above was used. From September 2001, option 2 is used. Option 2 will be standard procedure in the future. Since there is interest to use also option 1, this will be used on some orbits (proposals are welcome).

EFW internal burst (Mats André, Anders Eriksson)

In addition to the Burst mode of Cluster according to the Master Science plan, there is an internal EFW burst mode. The internal EFW memory is emptied at the beginning of every acquisition period.

Memory 1Mb = 500 kSamples

Usage up to now:

Burst data are technically OK from June 2001. Before June, we used a non-zero initial threshold level (as stated in documentation probably based on ground experience) which gave a lot of empty and non-initiated burst memory dumps.

Plans for the near future:

Proposals for other modes, or specific modes in specific regions, are welcome.

Special orbits (Mats André)

Cluster special orbits are at this time not included in the MS plan. Possible EFW options include:
1) BM with 3 EFW signals (2 Langmuir-mode + 1 E-vector)
2) BM with 4 signals
3) NM 180Hz filter on all spacecraft

Options 1) and 2) require relocation of telemetry within WEC.

Proposals for EFW special operations are always welcome (even in the absence of ``official´´ Cluster special orbits). .

Future meetings

1 October 2001, 1300 - WEC data and operations at ESTEC
2 October 2001, - SWT at ESTEC
3-6 October 2001 - ESTEC Cluster Workshop, see http://solarsystem.estec.esa.nl/~hlaakso/Cluster/Workshop.html
15-19 October 2001 - Cluster Ground based Workshop
18 October 2001 - Cluster SOWG
10-14 December 2001 - Fall AGU
22-26 April 2002 - EGS

A Cluster Workshop in February is discussed to take place in February 2002, and should concentrate on tail phenomena (Harri Laakso).

Science presentations

For further information, contact the speakers (see email in the list of participants). The afternoon session of Friday September 7 began with a silent moment in memory of B. Wilken

Software packages (Anders Eriksson, Tobias Eriksson, Harri Laakso)

Anders: EFW is fortunate enough to have two (almost) independent data analysis tools: Anders: Isdat demonstration: Vps + despinned E data from Cluster CD + 4s resolution Bz from PP CDF files in one plot.

Harri: Described shortly SDT. Used to work with SDT 5 years and in SDT finds following options useful:

EFW on the web

To appear:

Upcoming EFW meetings

There will be no more major EFW meeting in Uppsala this year. The ESTEC workshop in early October will be used for several informal EFW discussions. An informal EFW get-together should also be arranged during fall AGU in San Francisco December 10-14.

Presentations in electronic form

Anders Eriksson, EFW Operations http://cluster.irfu.se/efw/ops_files/ops.pdf