***** File MAG.DOC                                                                                                                
                                                                                                                                  
                                                                                                                                  
                            I. BACKGROUND                                                                                         
                                                                                                                                  
                                                                                                                                  
        On September 11, 1985, the International Cometary Explorer (ICE;                                                          
 originally called ISEE-3) spacecraft made in situ measurements of                                                                
 particles, fields and waves as it traversed the plasma tail of comet                                                             
 Giacobini-Zinner (G-Z). The time of closest approach was approximately                                                           
 11:02 UT and occurred at a tailward distance of 7,800 km. The spacecraft                                                         
 was inside the bow wave for roughly 3 hours and in the main tail for about                                                       
 10 min (Brandt et al., 1985;  Brandt et al., 1988, and references                                                                
 therein).                                                                                                                        
	                                                                                                                                 
        Data from some of the instruments on the ICE spacecraft are                                                               
 included on this CD-ROM archive for the period 08-14 September, 1985.                                                            
 Ephemeris data giving hourly values of the ICE spacecraft trajectory                                                             
 relative to Earth, Sun and G-Z are included in a separate file. Note                                                             
 that the deviation of the spacecraft from uniform linear motion was                                                              
 negligible during the encounter, so that interpolation of the trajectory                                                         
 is straightforward.                                                                                                              
                                                                                                                                  
        Magnetic field data were obtained by the Jet Propulsion                                                                   
 Laboratory (JPL) magnetometer (Frandsen et al., 1978) which provided                                                             
 three orthogonal vector measurements every 1/3 sec during the G-Z                                                                
 encounter. Plasma electron measurements were supplied by the Los                                                                 
 Alamos National Laboratory (LANL) plasma analyzer (Bame et al., 1978)                                                            
 every 24 seconds. No plasma ion measurements were made during the ICE                                                            
 traversal of G-Z.                                                                                                                
                                                                                                                                  
        The first scientific results from the ICE encounter with comet                                                            
 Giacobini-Zinner have appeared in Science (vol. 232, 1986), and further                                                          
 findings of the mission are contained in the March and April 1986 issues                                                         
 of Geophysical Research Letters, and in many other sources (e.g., McFadden                                                       
 et al., 1987; McComas et al., 1987, and references therein).                                                                     
                                                                                                                                  
                                                                                                                                  
 References:                                                                                                                      
 ----------                                                                                                                       
                                                                                                                                  
 Bame, S.J., J.R. Asbridge, H.E. Felthauser, J.P. Glore, H.L. Hawk, and                                                           
 J. Chavez, ISEE-C solar wind plasma experiment, IEEE Trans. Geosci.                                                              
 Electron., GE-16, 160-162, 1978.                                                                                                 
                                                                                                                                  
 Brandt, J.C., M.B. Niedner, and T. von Rosenvinge, "The ICE Project,"                                                            
 Adv. Space Res., v.5, 3-16, 1985.                                                                                                
                                                                                                                                  
 Brandt, J.C., "The International Cometary Explorer (ICE) Mission to                                                              
 Comets Giacobini-Zinner and Halley" in "Space Missions to Halley's Comet",                                                       
 p. 99-115, R. Reinhard, B. Battrick (Editors), ESA SP-1066, ESA                                                                  
 Publications Division, Noordwijk, The Netherlands, ISBN 0379 6566, 1986.                                                         
                                                                                                                                  
 Brandt, J.C., R.W. Farquhar, S.P. Maran, M.B. Niedner, Jr., and T.T.                                                             
 von Rosenvinge, "The International Cometary Explorer" in "Exploration                                                            
 of Halley's Comet. Based on the 20th ESLAB Symposium, held in                                                                    
 Heidelberg, F.R.G., 27-31 October 1986," p. 969-980.                                                                             
 M. Grewing, F. Praderie, R. Reinhard (Editors). Springer-Verlag,                                                                 
 Berlin, F.R.G. 23+984 pp. ISBN 3-540-17344-7 (F.R.G.), ISBN                                                                      
 0-387-17344-7 (USA), 1988.                                                                                                       
                                                                                                                                  
 Frandsen, A.M.A., B.V. Connor, J. van Amersfoot, and E.J. Smith, The                                                             
 ISEE-C vector Helium magnetometer, IEEE Trans. Geosci. Electron.,                                                                
 GE-16, 195-198, 1978.                                                                                                            
                                                                                                                                  
 McComas, D.J., J.T. Gosling, S.J. Bame, J.A. Slavin, E.J. Smith, and                                                             
 J.L. Steinberg, The Giacobini-Zinner magnetotail: Tail configuration                                                             
 and current sheet, J. Geophys. Res., v.92, 1139-1152, 1987.                                                                      
                                                                                                                                  
 McFadden, L.A., M.F. A'Hearn, P.D. Feldman, H. Bohnhardt, J. Rahe,                                                               
 M.C. Festou, J.C. Brandt, S.P. Maran, M.B. Niedner, A.M. Smith, and                                                              
 D.G. Schleicher, Ultraviolet spectrophotometry of comet                                                                          
 Giacobini-Zinner during the ICE encounter, Icarus, v.69, 329-337,                                                                
 1987.                                                                                                                            
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                      II. MAGNETIC FIELD DATA                                                                                     
                                                                                                                                  
 These data were obtained from the JPL magnetometer experiment on ICE                                                             
 (Principal Investigator: E.J. Smith; data provided by J. Wolf). The                                                              
 instrument produces three, high-accuracy, triaxial measurements per                                                              
 second of the  magnetic field strength in 8 ranges, i.e., +/-4 nT                                                                
 (lowest full  range), 14, 42, 144, 640, 4000, 22000, and 140000 nT                                                               
 (highest full range) and a sensitivity of 1/256 of each full range,                                                              
 in a 0-3 Hz pass band. During the G-Z encounter the instrument range                                                             
 was switched automatically between the 4 lowest ranges depending on                                                              
 the field intensity, giving sensitivities of 0.015, 0.051, 0.17 and                                                              
 0.57 nT respectively.                                                                                                            
                                                                                                                                  
 There is one ASCII data file for each day (Sept. 10-14, 1985). All the data                                                      
 files have an MS-DOS file name extension of .TAB (for 'Table'). Each logical                                                     
 record contains the year, day-of-year (day 1 is Jan. 1), hours, minutes,                                                         
 seconds, Bx, By, Bz, and Bmagnitude in the format (1X, I2, I4, 2I3, F6.2,                                                        
 4F8.3, 2X). Thus, each logical record has the following structure:                                                               
                                                                                                                                  
     Item   Bytes        Quantity         Format                                                                                  
     ----   -----        --------         ------                                                                                  
                                                                                                                                  
       0    1            blank              1X                                                                                    
       1    2-3          Year (e.g., 85)    I2                                                                                    
       2    4-7          Day of year        I4                                                                                    
       3    8-10         Hour               I3                                                                                    
       4   11-13         Minute             I3                                                                                    
       5   14-16         Seconds            F6.2                                                                                  
       6   20-27         Bx                 F8.3                                                                                  
       7   28-35         By                 F8.3                                                                                  
       8   36-43         Bz                 F8.3                                                                                  
       9   44-51         Bmag               F8.3                                                                                  
      10   52-53         blank              2X                                                                                    
(plus a carriage return and line field makes each row 55 bytes).                                                                  
                                                                                                                                  
 The time is UT and the magnetic field values are in nanoteslas.                                                                  
                                                                                                                                  
 Example: the first 2 logical records of the first day's data should appear                                                       
 as follows after separation from the byte stream:                                                                                
                                                                                                                                  
   YR DAY  H  M   SEC    Bx      By       Bz     Bmag                                                                             
  >85 253  0  0   .04  -3.684   6.139   1.808   7.385  <                                                                          
  >85 253  0  0   .38  -3.598   6.156   2.001   7.406  <                                                                          
                                                                                                                                  
 The time resolution is 1/3 second from the start of Day 253 until Day 255,                                                       
 18:38. At that time the bit rate dropped from 1024 to 512 bps, and the                                                           
 time resolution decreased to 2/3 sec. The data coverage and approximate                                                          
 file sizes are as follows:                                                                                                       
                                                                                                                                  
    File 1:   1985 Sept. 10, Day 253     91%    12.9 MBytes                                                                       
    File 2:   1985 Sept. 11, Day 254     99%    14.1 MBytes                                                                       
    File 3:   1985 Sept. 12, Day 255     98%    12.4 MBytes                                                                       
    File 4:   1985 Sept. 13, Day 256     95%     6.7 MBytes                                                                       
    File 5:   1985 Sept. 14, Day 257     83%     5.9 MBytes                                                                       
                                                                                                                                  
 The coordinate system for the magnetic field components is the I,S                                                               
 coordinate system, defined by the JPL group before launch. I is the unit                                                         
 vector in the direction of the ICE spin axis (positive in the northward                                                          
 direction), and S is the unit vector from the spacecraft to the Sun.  The                                                        
 z-axis is equal to I, the y-axis to the normalized cross-product I x S,                                                          
 and the x-axis to Y x Z.  The I,S coordinate system is approximately the                                                         
 same as the Solar Ecliptic (SE) system since the spacecraft z-axis is                                                            
 maintained within half a degree of perpendicular to the Ecliptic plane.                                                          
 (SE is defined the same way as GSE, but with the spacecraft [point of                                                            
 observation] substituted for Earth).                                                                                             
                                                                                                                                  
 While the JPL reduction program eliminates most noise spikes, there is a                                                         
 small number that do appear in these data. JPL does not hand-edit the high                                                       
 resolution data, since there is such a volume of it. Users should check                                                          
 for noise spikes when doing averaging or other analyses. There is no                                                             
 special flag for "bad" or missing data. A scan of the 5 days of high                                                             
 resolution data at JPL revealed the following noise spikes:                                                                      
                                                                                                                                  
              Time              Field magnitude                                                                                   
              ----              ---------------                                                                                   
                                                                                                                                  
        Day 253, 10:11:59.84        47.25                                                                                         
        Day 254, 03:51:28.21        59.17                                                                                         
                 04:05:17.84        56.19                                                                                         
                 10:10:55.31        59.68                                                                                         
                 11:06:13.15       128.07                                                                                         
                 12:04:23.92        62.73                                                                                         
        Day 255, 09:07:17.48        57.75                                                                                         
                 09:07:17.82       185.49                                                                                         
        Day 256, 07:35:54.94        57.58                                                                                         
                 21:08:09.00        23.83                                                                                         
                 23:01:15.94        35.20                                                                                         
        Day 257, 10:08:07.77        46.06                                                                                         
                 20:03:15.75        51.07                                                                                         
                                                                                                                                  
 The following information (and the table of noise spikes given above) has                                                        
 been provided by J. Wolf (JPL), after examining plots of the magnetic field                                                      
 data during the comet encounter: The highest legitimate value of Bmagnitude                                                      
 is 59.21 at 11:01:01.29 on Day 254, at the time of closest approach to the                                                       
 comet. On Day 254, one should eliminate points with Bmagnitude greater                                                           
 than 40 from 09:00 to 11:00 and from 11:10 to 13:00. During the interval                                                         
 11:00 to 11:10, points with Bmagnitude greater than 60 should be eliminated.                                                     
 For the rest of this 5 day interval, one should eliminate points with                                                            
 Bmagnitude greater than 20 nT.