= SUM (Pi*Si*Fi) / SUM (Si*Fi). In the output records we also carry along, separately for the magnetometer and plasma data, the numbers N of input records contributing to the output values, the fractional coverage over the minute (FC = SUM (Si)/60) and a measure of the extent to which the computed

values are based on data taken within the minute of interest (DW = SUM (Si*Fi)/SUM (Si). (Nm, FCm, DWm) and (Np, FCp, DWp) are (N, FC, DW) values for magnetic field and plasma data respectively. We create 1-min output records for field and plasma data separately, using the approach above. For output plasma records, we typically get contributions from 1 or 2 input records, while for magnetic field output records, we get typically contributions from 4-5 input records. We do not include variance information for the output plasma data but we do for the output magnetic field data. The magnetic field variances are defined as V = SUM [Wi * (Pi-

)**2] / SUM (Wi) Here the weighting factors Wi are the Si*Fi products introduced above. The output records actually contain standard deviations of the magnetic field parameters, i.e., SQRT(V). 3.Despiking the magnetic field and plasma data The IMP magnetic field data has a significant number of apparent data spikes. The IMP plasma data set also has a significant number of apparent data spikes, sometimes in the nonlinear-fit-based parameter values, sometimes in the moment-based values and sometimes in both. We have undertaken to eliminate the most egregious spikes, while at the same time trying to eliminate the least amount of good data. (There is no certain way to automatically eliminate all spikes and only spikes.) We independently set to our standard fill value all the fit-based parameters (or moment-based parameters) of a given input record if that record has a spike in any one or more fit-based (or moments-based) parameters (flow speed, flow direction angles, proton density and thermal speed). Likewise for the magnetic field data. For any parameter P and for any record, we determine the mean

and standard deviation [sigma(P)] of the P values in the two preceding and two following points. We require that the time interval between the first and last of the points be no more than 15 minutes (magnetic field data) or 60 minutes (plasma data). For P = magnetic field magnitude, flow speed, density or thermal speed, we declare a spike if |P-

| > 4 * sigma(P) AND |P-

| > k(P) *

where k(P) = 0.2, 0.1, 0.3, or 0.3 for P = field magnitude, flow speed, density, or thermal speed, respectively. For P = magnetic field component, flow longitude or flow latitude angle, we declare a spike if |P-

| > 4 * sigma(P) AND |P-

| > k', where
k' = 1 nT for field components and k' = 4 deg for flow latitude and
longitude.
Note that this test is not effective in detecting spikes in the first or
second data point after or before gaps in solar wind data (which gaps
are not infrequent) nor in finding multi-point spikes (which are
infrequent).
4. Region flags
Each 1-min record has two region flags. First, we have
used the 1-min resolution IMP 8 bow shock database at
http://omniweb.sci.gsfc.nasa.gov/ftpbrowser/bowshock.html
to flag whether the record is in the solar wind or not,
using
0 = solar wind
1 = not solar wind
Second, we have included the MIT region flags included
in their input data set, wherein each record is flagged as
1 = solar wind
2 = solar wind or magnetosheath
3 = definitely not solar wind
Where the input plasma record(s) for a given 1-min output record
had a common region flag, the output record contains that flag
value. For the rare occasion where this was not the case, the
output record has flag = 4.
5. Miscellaneous other
Finally, we merge the 1-min magnetic field and plasma data
sets to create a 1-min field- plasma-merged data set.
The magnetic field latitude and longitude angle values in
the 1-min records were determined from 1-min magnetic field
Cartesian components. However, for the plasma data, flow
latitude and longitude values of (typically 1 or 2) input
records were averaged and these averages were used to compute
flow vector Cartesian components (except that the output
records contain the negative of the Vx value thereby determined
since the flow longitude angles have value zero along the -Xgse
axis. Thus flow latitude and longitude angles have the same
signs as the Vz and Vy components in GSE, i.e., positive for
flow from south and west of the sun, respectively.
Two more points about the flow angles are important. First,
the input plasma records contain plasma parameters determined
via both fits and moments. The fit-based flow longitude
angles have the aberration caused by the Earth's orbital motion
about the sun removed, while the moment-based flow longitude
angles do not have aberration effects removed. Our new 1-min
product includes both set of plasma parameters and preserves
the asymmetry in handling aberration effects. Second, flow
latitude angles of the input records have a 2-deg asymmetry
about zero. That is, long term averages are ~ 2 deg. This
effect is not understood by the MIT team, and has been included
in all MIT data sets (at MIT or NSSDC) to date. However, for
this new 1-min data set, we have opted to remove this offset
by subtracting 2.0 deg from all the input data. Thus long
term averages of the flow latitude and Vz values of this data
set should be near zero.
The plasma temperatures of this 1 min data set have been determined
from the thermal speeds (W) of the input data set using the algorithm
T (deg K) = 60.5 * W (km/s) **2.
The IMP ephemeris information carried in the records of this 1-min data set
is not as contained in the input field or plasma data sets but is based on
the "new" IMP 8 orbit produced at GSFC around the year 2000 using a
decade's worth of IMP shadow information. This new orbit is believed to
be more accurate than its predecessor by ~1 Re or even more at times,
from ~1990 onward.
6. The contents/format of records are:
Wd Format Fill values Parameters Units, Comments
1 I4 9999 Year 1992,1993,...
2 I4 999 Doy 1-366
3 I3 99 Hour 0-23
4 I3 99 Minute 0-59
5 I2 9 Bowshock Flag 0,1 See above
6 F8.2 9999.99 X, GSE IMP position component, Re
7 F8.2 9999.99 Y, GSE "
8 F8.2 9999.99 Z, GSE "
9 F8.2 9999.99 Y, GSM "
10 F8.2 9999.99 Z, GSM "
11 I2 9 Nm, Number of mag field points
12 I3 99 FCm, Coverage within minute See above
13 F5.2 9.99 DWm, Interior fraction See above
14 F8.2 9999.99 Field Magnitude Average <|B|>, nT
15 F8.2 9999.99 Magnitude of Avg Field Vr |**|,nT
sqrt( ^2+**