EFW is the Electric Fields and Waves instrument on each of the four Cluster satellites. Production of reliable general-purpose data at a higher resolution than the spin period is complicated, but through the Cluster Active Archive initiative these data will start to come on-line late in 2003. In the meantime, we make available the spin-fitted electric field produced onboard and transmitted in the housekeeping telemetry.

What is available?

24-hour-plotsof EFW spinfit data in PNG (for browsing) and PDF (for printing) formats. The plots are fully open to direct access.
ASCII data files in the Cluster Exchange Format (CEF) with an average time resolution of 5.15 sec. To get the ASCII data, you must register.

Page status and plans: Under construction.

Accessing plots: By clicking on a link-marked date in the table below, you will come to a page with a plot in PNG format (typical size 35 kB) for quick browsing. From this page, there are links to plots in PDF format (typically 250 kB) suitable for printing, and to the data in ASCII/CEF format. The latter are access controlled: see next paragraph.

Accessing data: As the data are not always easy to interpret and are subject to measurement errors, we need to know who uses them to be able to send warnings and update messages. If you consider using the data for any scientific purpose, you MUST contact the EFW team through the PI, Mats.Andre@irfu.se, as there are lots of pitfalls. The ASCII/CEF data therefore resides in a separate directory with access control, for which anybody can get a user name and password by applying to aie@irfu.se.

Data content: The first column in a data file is the time in the format yyyy-mm-ddThh:mm:ssZ. The data following data parameters are included in the files and plots:

V_ps -- the probe-to-spacecraft potential, approximately equal to the negative of the spacecraft potential and hence a quantity co-varying with the ambient plasma density.
E_sun -- the average sunward electric field in the spacecraft spin plane during one spin (approximately 4 s), obtained by fitting of a sinusoid. Due to the spacecraft spin axis staying within a few degrees from the GSE Z axis, E_sun is a close approximation of GSE E_X. Note: E_sun is particularly difficult to interpret -- see caveats below.
E_dusk -- the average duskward electric field in the spacecraft spin plane during one spin (approximately 4 s), obtained by fitting of a sinusoid. Due to the spacecraft spin axis staying within a few degrees from the GSE Z axis, E_dusk is a close approximation of GSE E_Y.
sigma -- the RMS value of the spin fit. As the fit is done to data covering 0 - 32 kHz, this will be the RMS of the wavefield from the spin frequency (0.25 Hz) to 32 kHz, plus additions from other data features not accounted for in the spin fits (e.g. the velocity wake structure often seen in solar wind data).

Plot content

The plotted quantities (V_ps, E_sun, E_dusk, sigma) are described in the "Data content" section above.
In each plot, the data from the different spacecraft are represented by the standard colours, i.e. SC1 black, SC2 red, SC3 green, SC4 blue.
In each plot, the data from the different spacecraft are offset from each other to enhance readability. The zero level of each plotted quantity is shown by a dashed line of the same colour as the graph itself.
Position data for SC3 are given below each plot. The fill value NaN is used to represent e.g. invariant latitude when the s/c is outside the magnetosphere.

Data gaps and fill values: Data may be missing because of operational and quality issues.

If there are no data at all for a day, there will be no files or plots.
If data from some spacecraft are missing for a full day, the data file for that s/c will be either missing or empty, and there will be no data from that s/c in the plots.
If all data for some time interval is missing for some s/c, this time interval will usually not be included in the data files, and will be seen as a gap in the plots.
If there is some data (V_ps and sigma, say) but not others (e.g. E_sun and E_dusk) for some time interval, the missing data will be replaced by fill values (zeroes) in the data file. In the plots, the missing data will always be seen as gaps.

Time resolution: The data are transmitted to ground in the housekeeping data each 5.15 seconds. However, as the data are spin fits, each data point pertains to one spin, i.e. to 4 seconds. The effect of this is that the data are irregularly sampled. Presently, the data are presented with the time stamp of the HK packet (appropriately shifted) in full seconds. Please note that this procedure gives a timing inaccuracy of up to 6 seconds to individual samples, though consecutive samples will always be separated by a multiple of 4 seconds.

Validation: The data are validated in a two-step process:

Removal of technically unsound data (due to non-nominal instrument setup etc), mainly by reuse of the CSDS validation files.
Bulk removal of data from regions where EFW commonly encounters measurment problems (i.e. at periods of high spacecraft potential in flowing cold plasmas in the polar cap and tail lobes)

The validation is thus quite crude and measurement errors will at times be signifcant. It is imperative that anybody who considers using the data for any scientific purpose contact the EFW team through the PI, Mats.Andre@irfu.se.

Caveats: All sorts of measurment errors may be present. In particular, the spurious but close to constant sunward electric field always present in double-probe electric field data has not been removed. For Cluster EFW, this typically is 0.5 - 1.5 mV/m, varying between individual probe pairs and to some extent also over time and with environmental conditions.

Coverage: As the data are taken from the housekeeping telemetry, which we always have, the source of this data set covers much larger fraction of time (prior to the start of 100% science data coverage in summer 2002) than does the science data set used for production of the CSDS data. On the other hand, significant parts are removed in the validation process.

Plots and data for 2001

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