INTRODUCTION:

  There are two types of data provided for the Polar EFI instrument.
1) The raw spin-period E-Field, B-Field, SC potential and position 
     data from the spacecraft.
2) The T(ransformed) data which corrects E for vxB and subtracts 
     a T-96 model B field from the B.

  The data are stored in .cdf files, which may be downloaded or displayed 
and manipulated using provided IDL routines.  Summary plots for quick 
viewing are also provided.  The data are provided by date, YYMMDD, in 24
hour increments for most of the storms of interest.

  Raw data are located in the "raw_data" directory with summary plots in
the "raw_plots" directory.  The B-field displayed in the raw summary
plots is detrended by 5 minutes.

  T(ransformed) data are located in the "T_data" directory with summary 
plots in the "T_plots" directory.


COORDINATE SYSTEMS:

  The E-field data are given in a coordinate system which is based on the
spin plane, as the spin plane E-field probes are are long enough to
generally give clean measurements.  Polar's spin axis varied throughout 
the mission, and also throughout the year due to it's cartwheel motion.
Therefore the spin plane orientation varies compared to, say, GSE.

The coordinate system of the E-field data gives two components in the 
spin plane:  
  X-Y: which lies very near the X-Y GSE plane and is defined as the 
        the most anti-sunward direction in the spin plane. 
   Z : which is pedendicular to X-Y and is in the spin plane and
        points genenerally very near the Z GSE direction.

  To convert these directions to more standard coordinate systems, the
direction of the spin axis for each day is give both in the the data 
directory and the summary plot directory in text format relative to GSE.

  The "Raw" magnetic field data are provided in GSE coordinates.

  The T(ransformed) B-field data are provided in the same coordinate
system as the E-field data with the 3rd component:
  56 : which lies along the spin axis and completes the system by the 
        right hand rule.


IDL CODE:

  To use the provided IDL code to view/manipulate the data, first  
change to the polar_efi directory, then type the following line at
the Unix prompt as written:

    setenv IDL_PATH "<IDL_DEFAULT>:+."

  You may then run IDL.

  There are separate programs for viewing/loading the raw and 
T(ransformed) data: cdaw_efi_raw_read.pro and cdaw_efi_t_read.pro

  Both programs work similarly.  (The header of each program gives a
full description).  The programs read the data in from the appropriate
data directory and stores them in "tplot", for those familiar with that
routine.  The data may also be returned as arrays from the programs.
If returned as arrays, the array is a 2-d array with [*,0] the Unix 
times of the data and [*,X] the data quanties.  There is also a 
string label array returned which gives the data quantity descriptions
and units in the order the quantities are in the data array.

  "cdaw_efi_raw_read.pro" provides the E-field, SC potential, B-field
and B-field detrended over 5 minutes.

  "cdaw_efi_t_read.pro" provides the E-Field - vxB, SC potential, B-field
and B-field - B_model.

  If using "tplot" to display the data, simply execute:

    print,cdaw_efi_t_read(011105)

for example, and use normal "tplot" routines.

  If loading the data arrays, execute:

    print,cdaw_efi_t_read(011105,data=data,dat_lbl=dtlb,position=pos,$
      pos_lbl=pslb,spin_ax_gse=spinax)

for example.

  In both cases: 1=success, 0=failure


03/13/05
--
John Dombeck
Space Plasma Physics Group
University of Minnesota