DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains hour averages of the interplanetary magnetic
field (IMF) measurements obtained by the triaxial fluxgate magnetometer
experiment on Voyager 1. Identical instruments on Voyager 1 and 2 were
designed to measure the IMF between Earth and Saturn (10 AU) during the
primary Voyager mission. The design and performance yielded absolute
accuracies to better than < 0.1 nT. In general, each component of the
hourly average has an uncertainty of up to (+/- 0.05 nT) in the region
beyond 10 AU. More accurate measurements can be obtained by special
processing of the data, but it was not feasible to do this for the
entire data set included here. The magnetic field magnitude in nT is
provided along with angles of the field vector in the spacecraft-
centered Heliographic (HG) coordinate system, also known as RTN.
Coordinate System
=================
Interplanetary magnetic field studies make use of two important
coordinate systems, the Inertial Heliographic (IHG) coordinate system
and the Heliographic (HG) coordinate system.
The IHG coordinate system is use to define the spacecraft's position.
The IHG system is defined with its origin at the Sun. There are three
orthogonal axes, X(IHG), Y(IHG), and Z(IHG). The Z(IHG) axis points
northward along the Sun's spin axis. The X(IHG) - Y(IHG) plane lays in
the solar equatorial plane. The intersection of the solar equatorial
plane with the ecliptic plane defines a line, the longitude of the
ascending node, which is taken to be the X(IHG) axis. The X(IHG) axis
drifts slowly with time, approximately one degree per 72 years.
Magnetic field orientation is defined in relation to the spacecraft.
Drawing a line from the Sun's center (IHG origin) to the spacecraft
defines the X axis of the HG coordinate system. The HG coordinate
system is defined with its origin centered at the spacecraft. Three
orthogonal axes are defined, X(HG), Y(HG), and Z(HG). The X(HG) axis
points radially away from the Sun and the Y(HG) axis is parallel to the
solar equatorial plane and therefore parallel to the X(IHG)-Y(IHG) plane
too. The Z(HG) axis is chosen to complete the orthonormal triad.
An excellent reference guide with diagrams explaining the IHG and HG
systems may be found in Space and Science Reviews, Volume 39 (1984),
pages 255-316, MHD Processes in the Outer Heliosphere, L. F. Burlaga
[BURLAGA1984].
Data Formats
============
field description (data before 1990)
----- ------------------------------
1. s/c id (1 = Voyager-1, 2 = Voyager-2)
2. UTC YY DDD HH where YY=year, DDD=day, and HH=hour
3. X X IHG position component (A.U. - IHG coordinates)
4. Y Y IHG position component (A.U. - IHG coordinates)
5. Z Z IHG position component (A.U. - IHG coordinates)
6. Range Heliocentric range = sqrt(X*X+Y*Y+Z*Z)
7. F1 Field magnitude (nT) ( avg(F2(48sec)) )
8. F2 Field modulus (nT) ( norm (B1,B2,B3) )
9. delta Latitudinal angle (degrees - HG coordinates)
10. lambda Longitudinal angle (degrees - HG coordinates)
field descriptor (data after 1990)
----- ----------------------------
1. s/c identification (FLT1=Voyager 1)
(FLT2=Voyager 2)
2. Time (UTC) decimal year format (90.00000 is day 1 of 1990)
3. The magnetic field strength, F1, computed from
high-resolution observations.
4. The elevation angle (degrees) in heliographic coordinates.
5. The azimuthal angle (degrees) in heliographic coordinates.
6. The magnetic field strength, F2, computed from hour
averages of the components. The components of B can be
computed from F2 and the two angles.
MAG field components may be recovered using F2, delta and lambda.
BR = F2*COS(lambda)*COS(delta) Fortran users need to convert
BT = F2*SIN(lambda)*COS(delta) degrees to radians before
BN = F2*SIN(delta) using trig functions.
Contact Information
===================
Principal Investigator:
Prof. Norman F. Ness
Bartol Research Institute
Univerity of Delaware
Newark, Delaware 19716-4793
Phone: (302) 831-8116
Fax: (302) 831-1843
Email: norman.ness@mus.udel.edu
Data Contact:
Dr. Len Burlaga
Code 612.2
NASA Goddard Space Flight Center
Greenbelt, MD 20771
Tel.: 301-286-5956
Fax: 301-286-1433
E-mail: len.burlaga@nasa.gov
References
==========
Behannon, K.W., M.H. Acuna, L.F. Burlaga, R.P. Lepping, N.F. Ness, and
F.M. Neubauer, Magnetic-Field Experiment for Voyager-1 and Voyager-2,
Space Science Reviews, 21 (3), 235-257, 1977.
Burlaga, L.F., Merged interaction regions and large-scale magnetic
field fluctuations during 1991 - Voyager-2 observations, J. Geophys.
Res., 99 (A10), 19341-19350, 1994.
Burlaga, L.F., N.F. Ness, Y.-M. Wang, and N.R. Sheeley Jr., Heliospheric
magnetic field strength and polarity from 1 to 81 AU during the
ascending phase of solar cycle 23, J. Geophys. Res., 107 (A11), 1410,
2002.
Ness, N., K.W. Behannon, R. Lepping, and K.H. Schatten, J. Geophys.
Res., 76, 3564, 1971.
Ness et al., 1973
Acknowledgement
===============
Use of these data in publications should be accompanied at minimum by
acknowledgements of the National Space Science Data Center and the
responsible Principal Investigator defined in the experiment
documentation provided here.
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CONFIDENCE_LEVEL_NOTE |
These data have been extracted from the NSSDC archive for distribution
by the PDS along with other Voyager solar wind data sets. These data
were not submitted to the PDS for archive and have not been through
the PDS peer review process. These data are provided by the PDS for
the convenience of PDS users. Please exercise caution when using these
data.
At the time of experiment proposal, it was expected that the required
accuracy of the measurements would be 0.1 nT, determined by the combined
noise of the sensors and the spacecraft field. The spacecraft magnetic
field at the outboard magnetic field sensor, referred to as the primary
unit, was expected to be 0.2 nT and highly variable, consistent with
current estimates. Hence, the dual magnetometer design ([NESSETAL1971],
[NESSETAL1973], [BEHANNONETAL1977]).
At distances > 40 AU, the heliospheric magnetic fields are generally
and 85 AU is about 0.15 nT and 0.05 nT, respectively. The use of roll
zero levels for the two independent magnetic axes that are perpendicular
to the roll axis (which is nearly parallel to the radius vector to the
Sun) at intervals of about 3 months. There is no roll calibration for
the third magnetic axis. Comparison of the two derived magnetic vectors
from the two magnetometers permits validation of the primary
magnetometer data with an accuracy of 0.02 to 0.05 nT. A discussion of
the uncertainties that must be considered when using these data is given
in the Appendix of Burlaga et al. [1994] and in Appendix A of
[BURLAGAETAL2002].
The data beyond 40 AU (1990) are included in a separate file.
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