00readme.txt - NSSDCftp Directory: This subdirectory contains daily files of 40.5 sec Helios magnetic field and plasma data described below. It also contains a file of software written by Aaron Roberts, readhelios40s_dat.pro, for creating alfvenicity graphs. The Helios mission consisted of two spacecraft launched into the inner heliosphere, both executing orbits from 0.3 to 1 AU with roughly a six month orbital period. Magnetic field data were recorded at high resolution, with plasma data recorded at approximately 40.5 s resolution. These datasets give the highest resolution plasma (proton and helium) moments with the corresponding average magnetic field for each plasma measurement. There are results from two plasma sensors, one of which gives the vector velocity. The coverage is best in the early years and varies considerably for the rest of the mission. The files "Helios1_stats" and "Helios2_stats" give the year, day of year, number of points, and percentage of possible points for the days included in the sets. There is no coverage for many days, with the main reason being that the spacecraft pass behind the Sun with respect to the Earth, thus cutting off communication. The overall intervals covered are: Helios 1: 1974 day 346 to 1985 day 247 Helios 2: 1976 day 017 to 1980 day 068 The present set of files were produced by R. Schwenn and obtained from J. Luhmann. They have been reformatted by Aaron Roberts to assure spaces between the variables, and in the process the HGI longitude and the "RTN" versions of the variables were added for convenience. Also, spacecraft positions were interpolated to make them distinct. The fill value for missing data in the original files was either -1 or 0; all these have been changed to 0. The other entries are directly from the original files. R. Schwenn should be acknowledged for plasma data and F. Neubauer for magnetic field data. GSFC/SPDF's nssdcftp (or successor) should be acknowledged as the immediate source of the data. There are 34 fields in these ASCII datasets. There is a one-line header with the variable names in each file. The format for writing was 34(f12.4, 1x), and the variables are (in order): year Four digit year day Day of year, 1 = Jan 1 dechr Decimal hour hour Hour min Minute sec Second rh Heliocentric distance (AU) esh Earth-sun-spacecraft angle (deg) clong Carrington longitude (deg) clat Carrington/HGI latitude (deg) HGIlong HGI Longitude (deg) br The HGI "R" component of the magnetic field* (nT) bt The "T" component of the magnetic field (nT) bn The "N" component of the magnetic field (nT) vp1r The "R" component of the proton velocity (km/s) vp1t The "T" component of the proton velocity (km/s) vp1n The "N" component of the proton velocity (km/s) crot Carrington rotation np1 Proton number density (cm^-3) vp1 Proton speed (Km/s) Tp1 Proton Temperature (K) vaz Azimuth of the velocity vector (deg) vel Elevation of the velocity vector (deg) Bx SSE (spacecraft) X component of the magnetic field By SSE (spacecraft) Y component of the magnetic field Bz SSE (spacecraft) Z component of the magnetic field sBx Standard deviation of the BX component over the 40.5 s sBy Standard deviation of the BY component over the 40.5 s sBz Standard deviation of the BZ component over the 40.5 s nal Alpha number density (cm^-3) val Alpha speed (Km/s) Tal Alpha temperature (K) np2 Proton density (second instrument) vp2 Proton speed (second instrument) * The RTN components were calculated from the SSE XYZ components using R -> -X, T -> -Y, and N -> Z. The Cartesian coordinates for B and the angles for V are the original variables in the file, and no correction was made in the conversion to RTN for the actual spacecraft position. Since RTN and SSE are defined relative to the helioequatorial plane and to the ecliptic plane, respectively, and since these planes are inclined by 7.25 degrees relative to each other (heliocentric orbits of Earth, Helios 1 and Helios 2 are virtually co-planar), this introduces errors of up to 100% * (1 - cos 7.25) = 1% in the RTN components. However, the V and B are consistent with each other and can be compared directly. (text by Aaron Roberts, with edits by Joe King; October, 2008)