## Voyager 2 Magnetometer Solar Wind Interplanetary Cruise Data Description ORIGINAL DATA_SET_NAME VOYAGER 2 SOLAR WIND MAGNETIC FIELD HGCOORDS 48SEC AVG V1.0 (VG2-SW-MAG-4-SUMM-HGCOORDS-48SEC-V1.0) START_TIME = 1977-08-20T15:19:47 STOP_TIME = 1989-12-31T22:08:33 PDS3 DATA_SET_RELEASE_DATE = 2009-02-16 PRODUCER_FULL_NAME = DR. LEONARD F. BURLAGA ## PDS4 Collections This document contains the data descriptions for the following collections: - data-hg-48s (urn:nasa:pds:vg1-mag-swind:data-hg-48s) ## Collection Description This document includes the Voyager 2 magnetometer solar wind data from the Interplanetary Cruise averaged to 48 second samples in Heliographic coordinates with additional termination shock data. ## Confidence Level These data have been extracted from the NSSDC archive for distribution by the PDS along with other Voyager solar wind collections. 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](https://doi.org/10.1029/JA076i016p03564). 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 A of [BURLAGAETAL2002](https://doi.org/10.1029/2001JA009217). #### Comments on the Voyager 2 48 sec termination shock data The average magnetic field strength produced by the spacecraft at the location of the outboard magnetometer of the dual magnetometers system on V2 varies between 0.1 - 0.2 nT, comparable to the most probable magnetic field strength in the inner heliosheath and significantly larger than the most probable magnetic field strength in the distant supersonic solar wind. The spacecraft magnetic field is a complex, time-dependent signal that must be removed from the measured magnetic field signal in order to derive the ambient magnetic fields of the solar wind and heliosheath. Corrections must also be made for spurious magnetic signals and noise associated with the telemetry system, ground tracking systems, and other factors. A non-periodic modulation of the spacecraft's magnetic field, with amplitudes comparable to the average ambient magnetic field strength and periods in the range from 1 to 12 hours, has been present approximately half the time in the V2 data since ~1990, beginning in ~1985. Finally, a spacecraft systems command during late 2006 had the unintended consequence of exposing the sensors to temperatures well beyond their design limits for more than one week. This command also rotated one set of dual triaxial sensors through a large angle and produced additional noise, drifts and spurious signals as a result of damage to the sensor assembly. Extracting the signal describing the solar wind and heliosheath from the many sources of uncertainty is a complex and partly subjective process that requires understanding of the instrument and judgment based on experience in dealing with the ever-changing extraneous signals. We estimate that the 1-sigma uncertainty in the 48 sec averages in the components of the magnetic field is typically ~ +/-0.03 nT. The uncertainties in F1, BR, BT, and BN can differ from one another and they may vary with time, but there is no practical way to determine these uncertainties more precisely at present. ## Data Processing 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. The high resolution data submitted to the NSSDC has its origins in the original MVS 'Summary' data sets formally produced on the NSSC IBM MVS mainframe system. The original data sets contain a mix of engineering, electron, magnetic field and plasma data. The Voyager magnetometer (MAG) experiment now resides on a dedicated workstation where only MAG data are processed. ## 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 - The Y(HG) axis is parallel to the solar equatorial plane and therefore parallel to the X(IHG)-Y(IHG) plane. - The Z(HG) axis is chosen to complete the orthonormal triad. A 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](https://doi.org/10.1007/BF00173902), L. F. Burlaga. ## 48 Second Averaged Data Format The data consists of the following columns: 1. s/c identification (FLT1=Voyager 1) (FLT2=Voyager 2) 2. coordinate system (HG=heliographic)used for this data set 3. Time (UTC) format 4. field magnitude (nT) 5. field component 1 (nT) - HG 6. field component 2 (nT) - HG 7. field component 3 (nT) - HG 8. spacecraft radial distance (AU) 9. spacecraft x position (AU) - IHG 10. spacecraft y position (AU) - IHG 11. spacecraft z position (AU) - IHG ## 1 hour Averaged Data Format The data consist in two formats described below: ### Data before 1990 1. s/c identification (FLT1=Voyager 1) (FLT2=Voyager 2) 2. Time (UTC) format 3. X IHG position component (A.U. - IHG coordinates) 4. Y IHG position component (A.U. - IHG coordinates) 5. Z IHG position component (A.U. - IHG coordinates) 6. Heliocentric Range = sqrt(X*X + Y*Y+Z*Z) 7. Field 1 Magnitude (nT) (avg(F2(48sec))) 8. Field 2 modulus (nT) norm (B1,B2,B3) 9. Delta Latitudinal angle (degrees - HG coordinates) 10. Lambda Longitudinal angle (degrees - HG coordinates) ### Field descriptor (termination shock data) 1. s/c identification (2=Voyager 2) 2. Time (UTC) format YYYY DDD.DDDD YY = year DDD.DDDD = decimal day of year 3. F1 average field magnitude (nT) 4. Br field component (nT) - HG 5. Bt field component (nT) - HG 6. Bn field component (nT) - HG 7. 1 sigma error in F1 8. 1 sigma error in Br 9. 1 sigma error in Bt 10. 1 sigma error in Bn ## 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.