< 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.
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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)
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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/>
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SPDF Contact:
Natalia Papitashvili <Natalia.E.Papitashvili.1@nasa.gov>,
Ramona Kessel <ramona.l.kessel@nasa.gov>,
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Please acknowledge NASA's Space Physics Data Facility and
and relevant scientists identified above for data usage.
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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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