Earth's bow shock represents the outermost boundary between that region of
geospace which is influenced by Earth's magnetic field and the largely undisturbed
interplanetary medium streaming from the Sun. For many years this boundary has been
crossed by Earth-orbiting satellites. We have put together a web-accessible database
of bow shock crossings from IMP 8, Geotail, Magion-4, and Cluster to facilitate
statistical studies and cross-comparisons between satellites.
Further details on the sources and planned coverages of these data are given below.
The underlying ASCII files are
ftp-accessible.
The primary output from this interface is
one line per bow shock crossing containing parameters selected in the
left-most boxes below and with parameters satisfying any user-specified ranges
on the right side. Output will be sorted first by spacecraft and then by time,
unless the user specifies an alternative sorting below. A scatter plot output
option is also available.
The later words(24-36) were computed at SPDF.
Time tagging is addressed in footnote 1.
Scatter plot of any parameter pair with filtering
Please enter your selections and then click on the Submit button below.
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 first crossing in the interval (independent of the
in-out direction of spacecraft motion).
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; see below for discussion of flags)
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.
Further explanations of some equations below are given here
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)
But please check special note here also!
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 23 for duration.
17. Flag 1 (observation flag) has the following values -
1. Observed in field and plasma data
2. Field data missing
3. Plasma 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 (shock cleanliness flag) 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 (upstream cleanliness flag) 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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If you have any questions/comments about this service contact:
Dr. Natalia Papitashvili,
SPDF, Mail Code 672,
NASA/Goddard Space Flight Center, Greenbelt, MD 20771 |
