< ftp://spdf.gsfc.nasa.gov/pub/data/aaa_boundary_crossings/bowshock_crossings/00readme.txt>     
       
This directory contains the annual ASCII files of IMP-8
 Geotail, Magion-4, and Cluster 
bow shock crossing data that underlie the FTPBrowser
interface at https://omniweb.gsfc.nasa.gov/ftpbrowser/bowshock.html
The FTPBrowser and the text below show the record
formatand describes the multiple parameters in the records.

The basic IMP 8 observed parameters were provided by IMP magnetometer
 and plasma teams at GSFC (A. Szabo, J. Merka) and MIT
(J. Richardson, K. Paularena). The database will grow to encompass all
 1973-2001 IMP 8 bow shock crossings. 
Geotail bow shock crossings currently include 1995, 1996 and 1997 at 
the bow shock flanks but will grow to include all crossings from
1995 onward. The Geotail crossing were identified by R. Kessel (NSSDC). 
Two years worth - 1995, 1996 - of Magion-4 (Interball-Tail's sub satellite) 
bow shock crossings were supplied by J. Safrankova and Z.Nemecek. 
Cluster bow shock crossings were determined from the prime parameters by 
R. Kessel and students. Cluster crossings are currently
supplied for the first two years of operation - 2001 and 2002 - from one 
satellite, but will grow to include subsequent years.

There is one record per bow shock crossing. 
The derived parameters
(words 24-36) were computed at NSSDC.  Where some
but not all parameters could be determined, fill values of
strings of 9's (filled out to the format of the relevant
parameters) were used.

Creation of this data set and the FTPBrowser interface
were supported by the NASA Applied Information System
Research Program.

The records are in ASCII.  All columns have an extra
character (e.g., I4 for day number) to allow for spaces on
printing and to allow for unformatted reads by IDL and
other software.

Word    Name    Format          Comments
        
 1.      S/c     A2      Spacecraft ID (I8- IMP8, GE-Geotail, M4- Magion4, CL-Cluster)
 2.      Year    I5      YYYY
 3.      Dayofyr I4      DDD (1, 2, ... 365, 366)
 4.      Hour    I3      HH (0, 1, ... 23)
 5.      Minute  I3      MM (0, 1, ... 59)       see footnote 1
 6       Seconds I3      SEC(0-59)  for IMP8 are not avaliable 
 7.     Xgse    F6.1    Spacecraft position Xgse, units = Re
 8.     Ygse    F6.1
 9.     Zgse    F6.1
10.     Ygsm    F6.1
11.     Zgsm    F6.1
12.     Bxgse   F6.1    Xgse component of upstream magnetic field vector
13.     Bygse   F6.1
14.     Bzgse   F6.1
15.     Bygsm   F6.1
16.     Bzgsm   F6.1
17.     -Vxgse  F7.1      negative of Xgse component of upstream sw velocity
18.     -Vygse  F7.1      km/s, see footnote 3
19.     -Vzgse  F7.1      
20.     Density F6.1    upstream solar wind proton density (cm**-3) 
21.     Density F6.1    downstream solar wind proton density (cm**-3), footnote 4
22.     Temprtr I8      upstream proton temperature (deg K)
23.     Timspan I5      time span, minutes      see footnote 5
24.     Btot    F6.1    upstream magnetic field intensity, nT, footnote 6
25.     Flow spd F7.1     upstream flow speed, km/s, see footnote 7
26.     Soundspd F7.1     upstream sound speed, km/s, see footnote 8
27.     Alfvspd  F7.1     upstream Alfven speed, km/s, see footnote 9
28.     M'sonspd F7.1     upstream magnetosonic speed, km/s, cf footnote 10
29.     Ms      F5.1    upstream sonic Mach number, (wd 25)/(wd 26) 
30.     Ma      F6.1    upstream Alfven Mach number, (wd 25)/(wd 27)
31.     Mms     F5.1    upstream magnetosonic Mach number, (wd 25)/(wd 28)
32.     Beta    F8.2    upstream plasma beta, see footnote 11
33.     FlPres  F6.2    upstream flow pressure, nPa, see footnote 12
34.     Shst    F4.1    shock strength, (wd 21)/(wd 20)
35.     IMFcone I4      IMF cone angle, deg, see footnote 13
36.     IMFclck I4      IMF clock angle, deg, see footnote 14
37.      Orbno   I4      Orbit number, as per IMP Project
38.      Inout   I2      =0 for solarwindward orbit leg
                        =1 for magnetotailward orbit leg
39.      Seqno   I3      Sequence number of the crossing for this orbit
                        leg (1, 2, ...N; N will be an odd number except for
                        Transdr=2 cases), see footnote 15
40.      Transdr I2      direction of crossing transition
                        =0 spacecraft passing into solar wind
                        =1 spacecraft passing into magnetosheath
                        =2 non-resolvable shock(s), same domain (solar wind
                                or m'sheath) on both sides, see footnote 16 
41.     Flag1   I2      Observation flag, see footnote 17
42.     Flag2   I2      Shock cleanliness flag, see footnote 18
43.     Flag3   I2      Upstream cleanliness flag, see footnote 19
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Note: Parameters 21,23,34,37-43 are avaliable for IMP8 only 

Footnotes 

1. In general, the minute given is that in/during which the crossing is 
       observed.  For "extended" crossings, the minute given is that in which the 
       peak of the shock overshoot occurs.  For records recording multiple shock 
       crossings, the minute is the minute of the first shock crossing.

2.  Upstream parameters have been determined in various ways
      for various spacecraft.  For IMP 8, upstream parameters are
      as measured by IMP 8 on the solar wind side of the shock,
      typically over a few-minute interval judged by the IMP field
      and plasma teams as stable.  For Geotail and Magion, 10-min
      averages from the Wind spacecraft, time shifted to the bow
      shock using (Xwind - 14 Re) / Vx, were used.  This same
      approach was used for Cluster, but with ACE upstream data.
      For IMP multiple-shock records, all upstream parameters
      are for the most solarwind-ward shock crossing.


3.   The Xgse component of the solar wind velocity vector is negative.  To 
    avoid negative values for this component, we have chosen to give components 
    for the vector anti-aligned with the velocity vector.

4.     IMP 8: Note that for cases of multiple-shock
       records, the downstream density is that density just downstream 
       of the most solarwind-ward crossing.
       Other satellites: no downstream density is provided.

5.     IMP 8: The time span gives duration, in minutes, of gaps for inferred
       crossings (flag 1 = 4 cases) or duration of periods of multiple
       unresolved or resolved shocks (flag 2 = 6 or 7 cases).  
       For other cases, the time span gives the shock duration.  
       In the majority of cases wherein the shock occurs in a fraction of minute, 
       this field has value = 0.

-----------------------------------------------------------------------------------
Following footnotes address calculations of various parameters from direct observables.

6.  The field intensity is [Bx**2+By**2+Bz**2]**0.5 (wds 12-14 --> wd 24)

7.  The flow speed is [Vx**2 + Vy**2 + Vz**2]**0.5 (wds 17-19 --> wd 25)

8.  The sound speed = 0.12 * [T + 1.28*10**5]**0.5  (wd 22 --> wd 26)

9.  The Alfven speed = 20. * B / N**0.5  (wds 24, 20 --> wd 27)

10.  Magnetosonic speed = [(sound speed)**2 + (Alfv speed)**2]**0.5
        (wds 26, 27 --> wd 28)

11.  Plasma beta = [(T*4.16/10**5) + 5.34] * N / B**2
        (wds 22, 20, 24 --> wd 32)

12.  Flow pressure = (2.0/10**6) * N * V**2  (wds 20, 25 --> wd 33)
               (note that this 2.0 includes a 5% alpha contribution)

13.  IMF cone angle = 57.3 * arc cos [|Bx|/Bt]  (wds 12, 24 --> wd 35)

14.  IMF clock angle = 57.3 * arc tan [|Bygsm|/Bzgsm]  
        (wds 15, 16 --> wd 36)
---------------------------------------------------------------------------------------
Following footnotes apply only to IMP 8 data.

15.  Sequence number of the crossing for this orbit
         leg (1, 2, ...N) for multiple-shock records 
         (Flag2 = 6 or 7), this number increments by one
         for unresolvable shock periods (F2=6) or by the 
         number of resolvable shocks plus the number of 
         unresolvable-shock subintervals

16. Direction of crossing transition:
        =0 spacecraft passing into solar wind
        =1 spacecraft passing into magnetosheath
        =2 multiple close shocks; same region on both sides; see word 22 for duration.
                     
17.  Flag 1 has the following values -
        1. Observed in field and plasma data
        2. Field data missing
        4. Inferred crossing, data gap
        5. Inferred crossing, data but no likely shock visible
    When a bow shock crossing is inferred to have happened during some time 
    interval, the start time of the interval is given in the record.  
    In addition, if the interval is less than 30 minutes in duration,
    the location of IMP 8 at the start of the interval is also given in the record.
    Otherwise the IMP location words have fill values in them. Note that the
    time span word (word 23) is used to give the interval duration in such cases.
    In general, upstream parameter values are given as fill values for such cases. 
    These intervals typically correspond to data gaps (Flag 1 = 4) with
    IMP 8 clearly in the solar wind on one side of the gap and in the magnetosheath on
    the other side.  There are rare Flag 1 = 5 cases where IMP 8 is clearly in the
    solar wind on one side of the interval and in the magnetosheath on the other
    side and wherein there are data within the interval, yet it is impossible to
    discern on a finer scale when IMP 8 passed between the solar wind and the
    magnetosheath.
18.  Flag 2 has the following values.  
        (Note in particular that values 1-4
        are relevant to cases of one shock while 6-8 are relevant to
        cases of multiple close shocks where we hope to make a second
        pass to create individual records for resolvable close shocks; 
        note also that some or all of the members of a set of multiple 
        close shocks may be unresolvable from each other and, separately,
        may be ambiguous in the sense of values 2-4 for individual 
        shocks.  In general, where an interval of multiple close shocks
        ends with a clean shock, there will be a separate record for that
        shock.) 
        1. The shock is clean and unambiguous in all available data 
        2. The shock is clean in field, ambiguous in plasma data
        3. The shock is clean in plasma, ambiguous in field data
        4. The shock is ambiguous in all available data
        5. Used for inferred crossings (Flag1 = 4 or 5)
        6. Multiple unresolvable shocks possibly involving relatively
                clean shocks at the start and end  (Seqno, wd 39, 
                increments by 1 whether same domain or different domains 
                on two sides)
        7. Multiple resolvable shocks with no subinterval(s) of
                unresolvable shocks.  Used on first pass for intervals
                with no shock pair separated by >15 minutes.  Word 39
                increments by sum of number of shocks in the interval
                or one less if the ending shock is also given a 
                separate record of its own.
        8. Multiple shocks, mixed resolvable/unresolvable, some 
                resolvable shocks may be ambiguous.   Word 39 increments
                by the number of resolvable shocks in the interval or
                one less if the ending shock is given a record of its
                own.

19.   Flag 3 has the following values -
        1. Upstream values steady and well defined
        2. Upstream values unsteady and uncertainly defined
        3. Used for inferred crossings (Flag1 = 4) 
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Related data and directories:

SPDF Data and Orbits Services <http://spdf.gsfc.nasa.gov/>
-------------------------------------------------------------------
SPDF Contact: 
Natalia Papitashvili <Natalia.E.Papitashvili.1@nasa.gov>,
Ramona Kessel <ramona.l.kessel@nasa.gov>,

-------------------------------------------------------------
Please acknowledge NASA's Space Physics Data Facility and 
and relevant scientists identified above for data usage. 
--------------------------------------------------------
Authorizing NASA Official: Dr. R.E. McGuire, Head, SPDF, NASA Goddard Space Flight Center
                        301-286-7794, e-mail:  Robert.E.McGuire@nasa.gov
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