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Quality Flags <-- head the warnings!


Instrumentation Thresholds vs the target plasma distribution

 


Quasi-neutrality Check 

In v2.0 and greater L2 files, Ne and Ni are generally reliable.  Exceptions include:

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For L2 data, FPI densities were initially scaled by an overall factor to match those of plasma waves (fpi_waves_cmp.pdf). The overall sensitivity of DES and DIS can change with each FPI macro load in which the voltages applied to the MCP detector stack for each sensor are adjusted.  In Phase 1a, the relative sensitivity of DIS across spacecraft has not been observed to change.  The sensitivity of DES with respect to DIS has changed by ~10-20% over the course of commissioning and Phase 1a.  A correction factor for DES densities is derived from observations of DES and DIS in the magnetosheath.  The minimum time-scale for which a correction factor can be applied is an entire orbit, though in practice the same correction factor is typically used for all orbits for which the MCP voltage is unchanged.  Periods where changes in DES and DIS densities are correlated and have the same ratio as in adjacent quiet magnetosheath (where there are unlikely to be 'hidden' cold ions <10eV and the entire distribution is likely within FPI's energy range) intervals suggest that the entire relevant ion and electron distribution functions are being sampled. 

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Photoelectron Contributions

Internally generated photoelectons, unaffected by the spacecraft potential in the sun direction produce an effective cold electron component with density ~0.5-1 cm-3 and bulk velocity ~750 km/sec in the anti-sunward direction. This component varies with spacecraft spin phase. A model for this signal has been developed and the signal removed for the moment calculations as of software release v2.0.  Please see the separate page for more detailed information.  NOTE:  These photoelectrons (internal and spacecraft) are not removed from the skymap data product as users need to be aware of this signal for their specific data interval and how its removal might affect analysis and interpretations.

DIS fast survey measurements in the solar wind

Onboard summing of burst counts to form fast survey data products leads to increased numbers of counts/bin in fast survey skymaps.  In the solar wind, the maximum number of allowable counts in each bin is exceeded leading to clipping and resulting in a distortion of the plasma moments.

FPI burst data in the solar wind

FPI's field-of-view is binned with 11.25x11.25 deg resolution.  In the polar angle direction (+Z to -Z for each sensor), angular space is continually sampled.  However, the angular response in the azimuthal direction (X-Y plane) is <10deg. Therefore, as deflection states sweep out the azimuthal plane, there are gaps in the angular sampling of ambient plasma.  Sharp angular structure in both DIS and DES can lead to apparent 'spikes' in the plasma moments that are spin-phase dependent.  Such a phenomenon occurs often in high Mach number plasmas such as the solar wind.

Reasons spin-periodicities or Vz offsets may be present in the data: 

Background Radiation

 

Spin-periodicities  – Velocity Offsets

  • Compression artifacts, which can be different for Survey and Burst data products
  • Imperfect spectrometer response correction tables  (e.g., for signals dominating the very lowest or very highest energy channels; for data intervals very near a FPI macro change; and for data intervals for which sufficient burst calibration data was not readily available).  Some of these can be addressed with time.
  • Imperfect spacecraft potential or photoelectron signal correction.  For some data intervals, data users will necessarily need to apply custom corrections.
  • In some cases, even when the in-flight calibration tables have reduced the spin-period electron bulk velocity signal amplitude to below 50 km/s, there may appear more significant 20 s oscillations in the current density n*e*(Vi-Ve) (comparable to real current densities at the magnetopause).  This is a known issue and is currently beyond the scope of our current L2 processing.  If such current density oscillations are noticed, please contact the FPI team, and we will address these on a case by case basis until we are able to incorporate a correction into our routine L2 processing.

Compression Artifacts


Special Topic --> FPI in the solar wind

DIS fast survey measurements in the solar wind

Onboard summing of burst counts to form fast survey data products leads to increased numbers of counts/bin in fast survey skymaps.  In the solar wind, the maximum number of allowable counts in each bin is exceeded leading to clipping and resulting in a distortion of the plasma moments.

FPI burst data in the solar wind

FPI's field-of-view is binned with 11.25x11.25 deg resolution.  In the polar angle direction (+Z to -Z for each sensor), angular space is continually sampled.  However, the angular response in the azimuthal direction (X-Y plane) is <10deg. Therefore, as deflection states sweep out the azimuthal plane, there are gaps in the angular sampling of ambient plasma.  Sharp angular structure in both DIS and DES can lead to apparent 'spikes' in the plasma moments that are spin-phase dependent.  Such a phenomenon occurs often in high Mach number plasmas such as the solar wind.

Some burst segments may appear to look incomplete

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