Region: Solar Wind

Caution level: Low

EFW data in the solar wind is generally good. The one problem that frequently occurs is that of a velocity wake. This problem is easily seen and easily removed.

Known problems:

Problem Type	Frequency of Occurence	Ease of detection	Remediable?	Data Loss Severity
Velocity Wake	Frequent	Easy	Yes	Negligible

Examples of good EFW data in the solar wind

This data, from 2002-02-12, shows good agreement between both probe pairs of EFW (red, black) and CIS (blue). Low magnetic field strength results in no measurement by EDI. Offsets of 0.45 (P12) and 0.05 (P34) mV/m have been subtracted in the X direction. Note the small velocity wake in this data, which has been removed by the spinfitting routine. More information on figure quantities is given here.

Problem: Velocity Wake

Example of the problem	2002-02-12 0320 C3 Data from the solar wind, showing velocity wakes. The structures align with the +/-X direction. Description of the plotted quantities.
Description of the problem	A velocity wake is often seen wherein a spurious signal occurs on each probe as it passes through the antisunward direction.
How can it be detected?	The signature is easily seen in either the single-probe or double-probe (differenced) data. Since the solar wind flows always nearly in the -X direction, the wake occurs near 0 and 180 degrees.
How can it be corrected?	Simply remove the affected region near the wakes. Spinfits performed on the remaining data are valid.
Why does it occur?	The flow speed in the solar wind is often so high that the ions cannot fill in behind the spacecraft before reaching the EFW booms. The result is a spurious field when the boom points to within a few degrees tailward.
Other notes

Back to pitfalls and problems.

http://cluter.irfu.se/ops/problems/solar_wind.html
last modified on 28-Nov-2002