The MIT Faraday cup experiment on IMP 8 measures currents from solar wind ions, and from these measurements we calculate the velocity, density, and temperature of the solar wind. The IMP 8 data files consist of fine resolution data (approximately 1 minute resolution). IMP 8 spins with a period of approximately 2.7s. The Faraday Cup (FC) instrument scans the solar wind distribution stepping through a contiguous set of energy windows, one step per spacecraft spin. The FC instrument divides the spin into thirty-two, 11.25 degree angular sectors and integrates the measured currents over different angular sectors depending upon the Mode in which the instrument is operating. The border between two of the 11.25 degree angular sectors lies on the Sun-spacecraft line. The FC sensor collector plate is divided into two, semi-circular halves; the division line is parallel to the spacecraft spin plane which is approximately parallel to the ecliptic plane. The split collector allow determination of the bulk plasma flow relative to the spin plane; North/South angles refer to flows coming from above or below the spin plane respectively (flows from the South are designated as having a positive N/S angle). The bulk flow angle in the spin plane is determined from the measurements of current vs. rotation angle. The currents telemetered to the ground are the sums of currents for the two half-collectors ("A" and "B") and, for the TMS and AQM modes, also the current for the half-collector "B". Electrons are measured except for the eight angles near the Sun. The experiment has two memories only one of which is operating perfectly. As a result, only every other TMS spectrum is usable, and the time between spectra is usually twice that that would be expected from the spacecraft spin rate. The bad half-memory also limits the energy windows that can be used in the other modes, since they require both memories to hold the data. On occasion, the data are read out rapidly enough by the spacecraft to allow repeated use of the good half-memory, and the time resolution in the TMS is approximately 32 seconds.

Time

Spacecraft flag (6/7/8 = IMP 6/7/8)

Decimal year

Region flag provides an estimate of the region from which the data came. There are three flag values: * 1 - This time is definitely solar wind. * 2 - This time is either solar wind or magnetosheath, with no differentiation being made. This designation is used for multiple crossings between the solar wind and sheath regions. * 3 - This time is definitely NOT solar wind, being either magnetosheath or magnetospheric data.

Indicates the operating mode of the experiment. The following table describes the measurements for each mode. +---------------------------------------------------------------------------------------------------------+ Mode Mode Angles number Currents Energy windows Energy windows Number Name [deg] Protons Electrons ----------------- ---------------- ------------------ ----------- ------------------ -------------------- 2 Tracking (TMS) eight: 11.25 centered on Sun-spacecraft line; six: 45 for remainder of spin A+B and A 8* 4 3 Acquisition (AQM same as TMS same as TMS 24 21 1 Non-tracking (NTMS) eight, 45 A+B only 24 21 +---------------------------------------------------------------------------------------------------------+ *Selected so that the peak flux energy step of the prior distribution is the 3rd step of this measurement. Note that the mode names are historical and confusing: the NTMS mode has the greatest sensitivity because of the 45 degree angular sectors and hence longer integration times, but all the energy windows won't fit into the working side of our on board memory. So all the parameters will be in modes 2 or 3. In order to reduce the time between spectra, in the TMS mode the eight lowest electron energy windows are covered using four sets of two windows of increasing energy; those eight electron windows are thus covered in a sequence of four TM spectra.

Spacecraft position in GSE coordinates

Spacecraft position Y-component in GSM coordinates

Spacecraft position Z-component in GSM coordinates

(Better, from fits) Ion Flow Velocity (aberration corrected)

(From moments) Proton Flow Velocity (no aberration correction)

(Better, from fits) Proton most-probable thermal speed (aberration corrected). Thermal speed is the most probable thermal speed (i.e., the square root of [2kT/m(proton)]). To convert thermal speed to temperature in eV, multiply 0.0052 by the square of the thermal speed; to convert to temperature [K], multiply the square of the thermal speed by 60.5.

(From moments) Proton most-probable thermal speed (no aberration correction). Thermal speed is the most probable thermal speed (i.e., the square root of [2kT/m(proton)]). To convert thermal speed to temperature in eV, multiply 0.0052 by the square of the thermal speed; to convert to temperature [K], multiply the square of the thermal speed by 60.5.

(Better, from fits) Proton number density

(From moments) Proton number density

(Best, from fits) Proton East/West flow angle (aberration corrected). Azimuth is E/W, meaning bulk flow from the East or the West side of the Sun respectively. Positive azimuth angle means flow from the West.

(From moments) Proton East/West flow angle (no aberration correction). Azimuth is E/W, meaning bulk flow from the East or the West side of the Sun respectively. Positive azimuth angle means flow from the West.

(Better, from fits) Proton flow elevation angle (aberration corrected) from North or South of the spacecraft spin plane (almost identical to the plane of the ecliptic).Positive elevation angle means flow from the South. Threshsp values are determined from currents greater than a threshold value, below which we are not confident about the contribution of noise.

(From moments) Proton flow elevation angle (no aberration correction) from North or South of the spacecraft spin plane (almost identical to the plane of the ecliptic).Positive elevation angle means flow from the South. Thresh values are determined from all currents.