The ne_efw operator

In the magnetospheric lobes the particle density is often to low to be measured by other experiments.
This operator uses the electric potential from the Electric Field and Wave (EFW) instruments on the Cluster satellites.
This file define the constants in the equation
 Ne(EFW) = A * exp(-(Vs-Vp)/B)

 Ne is the density of electrons in cm^-3
 Vs is the spacecraft potential in V
 Vp is the probe potential in V
 -(Vs-Vp) is "Cluster X efw E py 10Hz any" in ISDAT, (X,y = 1,2,3,4)

 first ref. :
    Electron density estimations derived from spacecraft potential
    measurements on Cluster in tenuous plasma regions.
    A. Pedersen, B. Lybekk, M. Andre, A. Eriksson, A. Masson, F. S. Mozer,
    P.-A. Lindqvist, P. M. E. Decreau, I. Dandouras, J.-A. Sauvaud, A. Fazakerley,
    M. Taylor, G. Paschmann, K. R. Svenes, K. Torkar, and E. Whipple
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, A07S33, doi:10.1029/2007JA012636, (2008)

 second ref. :
   Solar cycle variations of the Cluster spacecraft potential and its use for
   electron density estimations
   Lybekk, B., A. Pedersen, S. Haaland, K. Svenes, A. N. Fazakerley, A. Masson,
   M. G. Taylor, and J.-G. Trotignon (2011),
   J. Geophys. Res., doi:10.1029/2011JA016969
A and B are constants determined by EUV and X-ray solar radiation that varies over the solar cycle. (p is probe and s is satellite).
Usage in Calculator:
     p0y = ne_efw(q0,q1,q2,q3,q4,'max_level') 
     q0 is Cluster X efw E pY 10Hz any
               X = 1,2,3 or 4
               Y = 3 on SC1, SC3 and SC4,  1 on SC2
     q1 is Cluster X efw E pY 10Hz any
               X same as on q0
               Y = 4 on SC1, SC3 and SC4,  2 on SC2
     q2 is Cluster X efw st whisper_transmit
              X same as on q0
     q3 is Cluster X efw st sweep_on
               X same as on q0
     q4 is CSDS_PP CX ASPOC I_ion__CX_PP_ASP  
        or CAA CX ASPOC IONC Ion Emission Current
               X same as on q0

The optional 'max_level' is the maximum probe potential in volt for the function.
The default value of 'max_level' is EFW_DENSITY_DEFAULT_LEVEL (-8.0).

The ne_efw operator returns EFW_FILLVALUE (-1.0) when one of:

  1. EFW probe potensial is greater than 'max_level'
  2. ASPOC ion current is greater than ASP_EPSILON, (0.001 μA).
  3. Whisper is transmitting
  4. EFW is sweeping
  5. EFW probe potential is saturated, (at minimum value)
The ne_efw returns the electron particle density Ne(EFW) in cm^-3 .

The constants A and B are found in the file ne_efw_def.h .

The values when the EFW probes are saturated are found in the file ne_efw_def.h .
The saturation value is about -68 Volt, and have slightly different values on all the 16 EFW probes, (4 SC * 4 probes /SC) .

The CSDS ASPOC data is not available after summer 2008.
After the ASP_SCX_IGNORE_AFTER dates given in the file ne_efw_def.h the fifth quantity (q4) can be repaced with another quantity, eg. Cluster X efw E pY 10Hz any.
X = 1,2,3 or 4
After this date the ASPOC ion current is ignored in this operator.

The EFW Ne calibration is valid only for C4. For the other spacecraft a correlation factor found in the file ne_efw_corr.h is used by this operator.

Updated Apr 11, 2016 by Bjørn Lybekk