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
---------- 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
----------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
-------------------- Plans for the
---------- Special orbits (Mats André)
Software packages (Anders Eriksson,
Tobias Eriksson, Harri Laakso)
EFW on the web
Upcoming EFW meetings
Presentations in electronic form
Anita Aikio firstname.lastname@example.org
Mats André email@example.com
Rico Behlke firstname.lastname@example.org
Jan Blecki email@example.com
Lars Blomberg firstname.lastname@example.org
Rolf Boström email@example.com
Stephan Buchert firstname.lastname@example.org
Tobia Carozzi email@example.com
Paul Eglitis Paul.Eglitis@irfu.se
Anders Eriksson Anders.Eriksson@irfu.se
Tobias Eriksson firstname.lastname@example.org
Carl-Gunne Fälthammar email@example.com
Georg Gustafsson firstname.lastname@example.org
Igor Ivonine email@example.com
Yuri Khotyaintsev firstname.lastname@example.org
Harri Laakso email@example.com
Per-Arne Lindqvist firstname.lastname@example.org
Elizabeth Lucek email@example.com
Björn Lybekk firstname.lastname@example.org
Göran Marklund email@example.com
Arnaud Masson Arnaud.Masson@esa.int
Kalevi Mursula firstname.lastname@example.org
Anssi Mälkki email@example.com
Annika Olsson firstname.lastname@example.org
Hermann Opgenoorth Hermann.Opgenoorth@irfu.se
Arne Pedersen email@example.com
Tuija Pulkkinen firstname.lastname@example.org
Kristof Stasiewicz email@example.com
Gabriella Stenberg firstname.lastname@example.org
David Sundqvist email@example.com
Pekka Tanskanen firstname.lastname@example.org
Anders Tjulin Anders.Tjulin@irfu.se
Jan-Erik Wahlund email@example.com
Andris Vaivads firstname.lastname@example.org
Lennart Åhlen email@example.com
Simon Walker firstname.lastname@example.org
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).
Wake. Strong signal at 1 Hz in despinned E can be caused by velocity
wake in dense plasma (magnetosheath, plasmasphere, solar wind).
Probe saturation. Problem can appear when probes were run with high
I_bias in dense plasmas. Until April, we had at least -180 nA on the probes,
causing occasional saturation. We have been using I_bias=-140nA since May
to avoid this problem. Large I_bias earlier was used to minimize the sunward
offset field. [For example, 2001-02-02 0407, p12 had different I_bias than
Asymmetry offsets. There are other asymmetries that can cause spin
frequency multiples: spheres are not identical, near environment of spheres
(wire, puck, guard) not symmetric with respect to sun, area of wire to
sphere is 10% of the sphere's area. Variations ~0.5 mV/m, sunward offset
field of the same magnitude can also be found.
Instrumental offsets. Creates offsets in p12 and p34. ACDC
is reset each data acquisition period. In most cases offsets smaller than
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
(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
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/
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:
Remove data when I_bias small (around 0 nA)
Remove data when WHISPER disturbs power spectra (only power removed)
Data are not removed when ASPOC is ON.
Other source in data screening: command logs, correspondence with JSOC
Automatic discarding of Whisper
Intercalibration with other instruments
Improvement of spectral calculation
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
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)
EFW is part of WEC
Master Science Plan http://jsoc1.bnsc.rl.ac.uk/
regulates telemetry allocation to WEC, and thus all our possibilities
Internal WEC coordination led by DWP group in Sheffield
Time sharing with ASPOC through bilateral agreement
Most used real time sampling
NM telemetry (1.4 kbit/s):
a. 2 E-field signals (V12, V34) at 25 samples/s
b. 4 single probe signals at 5 samples/s
BM1 telemetry (15 kbit/s):
a. 2 E-field signals (V12, V34) at 450 samples/s
b. 4 single probe signals at 5 samples/s
c. (occasionally) EFW can get more than 15 kbit/s (at the expense of
other WEC instruments), allowing 3 or 4 signals at 450 samples/s
a. Spin fit E-field (5.15 s resolution)
b. Spacecraft potential (5.15 s resolution)
I_bias on probes since start of mission (Feb 1):
a. February - April 2001: p1p2 -180 nA, p3p4 -220 nA
b. May: -180 nA on all
c. June onwards: -140nA on all
Voltage offset on puck (+1V now)
Voltage offset on guard (-6V now)
Extensive tests during commissioning
David Sundkvist in Uppsala is working on sweeps, particularly the varying
Brief (few seconds) bias sweeps are routinely made to determine:
a. photoelectron emission
b. sheath resistance (wave diagnostics)
c. plasma properties
Current as well as voltage sweeps made
Interval has normally been 30 mins-2 hours
Problem with the 10 Hz filter on probe 3, s/c2 (M. André, P.-A.
Since late in July 2001, the 10Hz filter on p3 of sc2 is not functioning
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
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
4 signal 9 kSamples/s ~14s
8 signal 9 kSamples/s ~7s
2 signal 450 Samples/s ~10minThere is usually one opportunity of
Burst per acquisition period (according to the MS plan). There are several
ways to trigger the burst. Large E-field is usually a good trigger. The
bursts can also be started at a certain time (time-tag)
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.
V12 and V34 at 18 kSamples/s (2 E-components), trig on bandpass filter
V3 and V4 at 18 kSamples/s (2 individual probes), trig on V12H (50
V1, V2, V3, V4 at 9 kSamples/s (4 individual probes), trig on V12M
V1,V2,V3,V4,BX,BY,BZ at 9 kSamples/s, time tagged (one test only
Plans for the near future:
Proposals for other modes, or specific modes in specific regions, are welcome.
Time tag trigger EFW burst (to get all 4 s/c simultaneously) with option
d) above (both E- and B-fields) in Cluster BM.
Trigger EFW burst within Cluster BM (NM if no BM).
Trigger EFW burst within WBD acquisition period.
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). .
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).
For further information, contact the speakers (see email in the list of
The afternoon session of Friday September 7 began with a silent moment
in memory of B. Wilken
P.Janhunnen, The occurrence frequency of auroral potential structures,
Polar EFI statistical study. A follow up study with Cluster was discussed.
A.Vaivads, Energy flux on auroral field lines.
A.Pedersen, First analysis of 3 March magnetopause and 17 March cusp crossings.
Where is the magnetopause in the cusp region? It should be useful to go
back and find magnetopause crossings with steady solar wind conditions.
M. André, Wave observations at the magnetopause.
E.Lucek, Cluster/FGM observations at the bow shock
R. Behlke, Electric field measurements of Short Large Amplitude Magnetic
A.Masson, & Olivier. Electron densities from EFW and WHISPER.
Automatic intercalibration between Cluster instruments.
G.Stenberg, Wave distribution function analysis. Looking for wave (E- and
B-fields) data from Cluster to apply specific analysis technique.
H.Laakso, ESTEC workshop. For updates, see http://solarsystem.estec.esa.nl/~hlaakso/Cluster/Workshop.html
Software packages (Anders Eriksson, Tobias Eriksson, Harri Laakso)
Anders: EFW is fortunate enough to have two (almost) independent data analysis
Anders: Isdat demonstration: Vps + despinned E data from Cluster CD + 4s
resolution Bz from PP CDF files in one plot.
Isdat (PI supported within WEC). Modules for EFW and all other WEC
data sets as well as for all CSDS data products. Runs on most unix systems
and VMS. General routines for all sorts of data, many application interfaces
including graphical client IGR, Matlab interface and unix command line.
Distributed as source code. See http://space.irfu.se/isdat/
for documentation, tutorials etc. Maintainer Tobias Eriksson, email@example.com.
SDT from Berkeley. EFW data only. Implements many useful features
for E-field analysis. Runs on Sun Solaris. Binary distribution. Maintainer
Jack Vernetti, firstname.lastname@example.org.
Harri: Described shortly SDT. Used to work with SDT 5 years and in SDT
finds following options useful:
coordinate systems (including field aligned)
Offsets can be specified
EFW on the web
Typical modes of EFW
FAQ, including calibration, intercalibration and warnings concerning
various effects (such as effects of spacecraft wakes)
Overview of the command log in human-readable format.
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