File vy1mgd.txt
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VOYAGER-1 INTERPLANETARY DATA
The main science objectives for the VOYAGER interplanetary mission are as
follows:
- investigate the structure of the solar wind magnetic fields and plasma
in the inner and outer heliosphere;
- conduct long term study of heliospheric evolution during different
phases of the twenty-two year solar magnetic cycle and the eleven-year
solar activity cycle;
- study the long term solar modulation and determine the elemental and
isotopic abundances of galactic cosmic ray particles in the heliosphere;
- measure radial gradients, spectra, and nuclear abundances of the
anomalous component of cosmic rays from acceleration at the solar wind
termination shock;
- investigate local particle acceleration in the interplanetary medium
from solar flare shocks and corotating interaction regions;
- study propagation of solar energetic particles in the heliosphere.
This directory contains hourly averages of parameters for the
interplanetary magnetic field, solar wind plasma and
spacecraft trajectory coordinates
VOYAGER-1 data have been reprocessed to ensure a uniformity of
content and coordinate systems relative to data from other deep-
space missions:
- All spacecraft trajectory data were transformed to a Heliographic
Inertial (HGI) coordinate system.
- calculation of the RTN Cartesian components of interplanetary magnetic
field from the RTN spherical components:
BR=|B|*cos(THETA)*cos(PHI)
BT=|B|*cos(THETA)*sin(PHI)
BN=|B|*sin(THETA)
where THETA - spherical RTN latitude, PHI- spherical RTN longtitude
- calculation of RTN Spherical components of the solar wind velocity from
RTN cartesian components:
V = (Vr^2 + Vt^2 + Vn^2)^0.5
THETA=asin(Vn/V)
PHI=atan(Vt/Vr)
where THETA - spherical RTN latitude, PHI- spherical RTN longtitude
- calculation of given thermal speed Vth into temperature T (Kelvin):
T=60.5*Vth^2 (Vth in km/s)
- merging of trajectory coordinates, magnetic field data, and plasma data
files into a single annual file VY1_YR.DAT, where YR is the year;
- Data gaps were filled with dummy numbers for the missing hours or entire
days to make all files of equal length. The character '9' is used to
fill all fields for missing data according to their format, e.g.
' 9999.9' for a field with the FORTRAN format F7.1. Note that format F7.1
below really means (1X,F6.1),etc.
For the daily resolution data (one file), simple averages were taken over
the hourly values. The format is identical to that for the hour averages
However, the "hour" field has 0 as a value.and the "Magnitude of Average
Vector" field is the simple average of the 24 hourly values of this parameter.
FORMAT DESCRIPTION
WORD ASCII MEANING UNITS/COMMENTS
1 I4 Year 1977, 1978, 1979, etc.
2 I3 Decimal Day January 1 = Day 1
3 I3 Hour 0,1,...,23
4 F7.2 Spacecraft Heliographic Astronomical units
distance
5 F7.1 Heliographic Inertial latitude Degrees, +/-90.
of the Spacecraft
6 F7.1 Heliographic Inertial longitude Degrees, 0-360
of the Spacecraft
7 F8.3 Field Magnitude Average |B| 1/N SUM |B|, nT
8 F8.3 Magnitude of Average Field sqrt(Bx^2+By^2+Bz^2), nT
9 F8.3 BR RTN-Coordinate System nanoteslas
10 F8.3 BT RTN-Coordinate System nanoteslas
11 F8.3 BN RTN-Coordinate System nanoteslas
12 F7.1 Proton flow speed, RTN km/s
13 F7.1 THETA-elevation angle degrees
of flow velocity vector
(RTN-cordinate system)
14 F7.1 PHI- azimuth angle of degrees
flow velocity vector.
(RTN-coordinate system) .
15 F9.5 Proton density [n/cc]
16 F9.0 Protom Temperature (calculated degrees, K
from thermal speed width
T=60.5*Vth*Vth)
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Notes on Voyager 1 and 2 Magnetometer Data After 1989.
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
(Ness et al., 1971; Behannon et al. 1977).
At distances > 40 AU, the heliospheric
magnetic fields are generally much weaker than 0.4 nT; the average magnetic field
strength near 40 AU and 85 AU is »0.15 nT and »0.05 nT, respectively. The use of roll
calibrations lasting »6 hours permits determination of the effective 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 »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 nT - 0.05 nT.
For further detail informaion look at
http://cohoweb.gsfc.nasa.gov/html/cw_data.html#vy_mag
DESCRIPTION OF COORDINATE SYSTEMS
The Heliographic Inertial (HGI) coordinates are Sun-centered and inertially
fixed with respect to an X-axis directed along the intersection line of
the ecliptic and solar equatorial planes. The solar equator plane is
inclined at 7.25 degrees from the ecliptic. This direction was towards
ecliptic longitude of 74.36 degrees on 1 January 1900 at 1200 UT;
because of precession of the celestial equator, this longitude increases
by 1.4 degrees/century. The Z axis is directed perpendicular and northward
from the solar equator, and the Y-axis completes the right-handed set. This
system differs from the usual heliographic coordinates (e.g. Carrington
longitudes) which are fixed in the frame of the rotating Sun.
The RTN system is fixed at a spacecraft (or the planet). The R
axis is directed radially away from the Sun, the T axis is the cross
product of the solar rotation axis and the R axis, and the N axis is the
cross product of R and T. At zero Heliographic Latitude when the
spacecraft is in the solar equatorial plane the N and solar rotation axes
are parallel.
Hour averages of the interplanetary solar wind data from, and hourly
heliocentric coordinates of, Voyager1/2 and other interplanetary spacecraft
may be also be accessed and plotted on-line through the COHOWeb service
http://cohoweb.gsfc.nasa.gov/
Acknowledgement:
Use of these data in publications should be accompanied at minimum by
acknowledgements of the Space Physics Data Facility and the responsible
Principal Investigator defined in the experiment documentation provided here.
Citation of SPDF's Coordinated Heliospheric Observations (COHO) data base
would also be appreciated, so that other potential users will be made aware of
this service.
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