Don:   I have polished the text and added our addresses and phone/fax Nos.
         below. Please have a final look and send out.
                                                  Regards,    Kolya.

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                                                         Nov.11, 1994
 
    This update (file name is GSM1194.DAT), of the magnetospheric modeling
dataset (see Fairfield et al., J.Geophys.Res., v.99, #A6, p.11319, 1994,
for details and the format description) has been generated on Nov.9, 1994.
It is based on the previous release of October 1993; the difference from the 
latter is that several glitches have been found and eliminated, as explained 
below.

  (1) Some records, in which the begin time and the center of the averaging 
interval did not belong to the same UT hour, were supplied with the wrong 
value of HOUR (word #3) (by 1 hour larger than the correct value).  This 
error could have affected calculations which explicitly used UT values from
the dataset. In this version, the erroneous UT values are replaced by correct
ones.

  (2) In the previous version, we used the solar wind parameters from the files
obtained via the online NODIS system. In that files, missing values of the
solar wind parameters were filled by 0's, which might lead to ambiguities in 
some cases. For example, records containing zeros for the solar wind speed 
could be easily recognized as "no-data" records, since V never falls to zero.
Similarly, it is very unlikely that all three components of the IMF simultane-
ously equal zero, so it could also serve as an indicator of the "no-IMF-data" 
records.
    However, this way of labeling the "no-data" records becomes ambiguous for 
such parameters as the elevation angle, Vlat, and the azimuthal angle, Vlon, of
the solar wind flow: it is impossible to distinguish between a "no-data" case
and that of strictly radial solar wind. 
    In creating this upgrade of the dataset, the CD-ROM version of the OMNI 
files were used, in which all digits of missing parameters were filled by 9's,
and that effectively solved the problem. All missing data are now filled by 
nines in the new version of the modeling dataset.

  (3) The old version did not completely match the data format description 
given in the Table 2 of the paper by Fairfield et al., J.Geophys.Res., v.99,
p.11319, 1994, in that the sequence of the flow angles Vlat and Vlon was oppo-
site to that given in the Table. Now the correct order is restored in the data
file so that it corresponds to the documentation: first Vlat and then Vlon.

  (4) Due to the interpolation between contiguous hours used for ISEE data, the
merging code generated "non-standard" digital equivalents for the Kp-index va-
lues, such as, for example, 18, 22, 29, etc., which do not correspond to any
elements in the sequence 0,0+,1-,1,1+,2-,2,2+,... .    However, we decided not
to change these values to standard ones, since, in some cases, such "rounding"
would be ambiguous. In any case, users interested in the Kp-index can easily 
make an appropriate standardization themselves.

  (5) It was also found that in a small number of HEOS-2 records at distances 
greater than 17 Re (records ## 45262-45585), the begin times (Bmin, word #4) 
were inadvertently set equal to zero, creating a small error in the timing. 
The associated averaging durations (Dmin, word #5) are also unreliable and the 
AE values are not exactly correct.) The HEOS field averages which, in contrast
to the rest of the data set, were prepared and provided to us by Principal 
Investigators (P.C. Hedgecock and B.T. Thomas) about 20 years ago, have several
important characteristics missing in their data format (e.g. the numbers of 
points in the averages, the r.m.s. deviations, and durations of the averaging 
intervals).  Some details of their averaging procedure are also not quite clear.
For these reasons, we are planning to reprocess all the HEOS data files, using
the original high-resolution data. When this is accomplished, the Bmin error 
described above will be corrected and the other omitted quantities restored.

                      N.A. Tsyganenko                D.H. Fairfield

     Internet:     ys2nt@lepvax.gsfc.nasa.gov    u2dhf@lepdhf.gsfc.nasa.gov
        Phone:     (301)-286-7925                (301)-286-7472
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