Some Descriptive Text

From top to bottom, the 4 panels represent the following solar wind proton parameters:

  1. the bulk speed in kilometers per second
  2. the density (protons per cm3)
  3. the most probable thermal speed (km/sec) = Sqrt(2kT/m)
  4. the flow direction in the plane perpendicular to the ecliptic plane, with positive values indicating flow FROM the south. On rare occassions the spacecraft's roll angle is changed for brief periods, during which the derived flow direction will refer to a different plane. A list of such times is available.

The Proton Monitor (PM) is a subsensor of the MTOF instrument, which is one of the 3 time-of-flight instruments comprising the CELIAS experiment on the SOHO spacecraft. MTOF determines high resolution mass spectra of heavy solar wind ions and uses a very wide bandwidth energy-per-charge analyzer to maximize counting statistics. The PM was designed to assist in the interpretation of MTOF data and for that reason uses a similar wide bandwidth analyzer that limits the accuracy of derived solar wind parameters. In addition, since SOHO is not a spinning spacecraft, the deflection system was designed to have a wide angular acceptance (+- 15 deg). For technical reasons this leads to an ambiguity between incident angle and incident energy/charge; this ambiguity was designed into the PM to match as closely as possible the behavior of the deflection system for the main MTOF sensor. It is not the energy/charge but rather the mass/charge that is needed for interpretation of the MTOF mass data.

The data presented here are derived from sets of 6 rates (one for each voltage step of the PM deflection system) obtained every 30 seconds. The voltage steps are spaced logarithmically (about 60% step size) from about 0.3 to 3 kV. At a given voltage step the energy per charge dynamic range is slightly more than a factor of 2. The overall geometry factor of the PM is about 1.0 x 10**-4 cm**2.

SOHO is never in the magnetosphere and enjoys excellent data coverage. The data on the Web page are typically between a few minutes and a few hours old.

The data are obtained by automatic electronic transfer from the Experimenters' Operations Facility (EOF), located at GSFC, to the University of Maryland. A batch file 'wakes up' every 15 mins to determine if any new files have arrived. If so, the data is processed to determine the rates, which are then compared with the simulations to determine the solar wind parameters. These parameters are then automatically plotted by another procedure that in turn updates the pointers on the Web page.

Typically one 'REL' file is received every half hours and contains a half hour of data. These data are then processed and plotted in the 48-hour plots (using 2-min averages) within a few minutes of receipt. Hence the age of the last plotted data normally ranges from a few minutes to a few hours. Approximately once per day we receive a long 'QKL' file that results in an additional delay of about 4 hours. At intervals the space craft is tracked continuously for a period of several months, eliminating the delay associated with the QKL file. During spacecraft orbit-trim maneuvers (approximately every 2 months) the PM deflection system is turned off, resulting in a data outage lasting a day or two.

The 2-week plots are generated once per day and use 15-minute averages.

The 27-day (Carrington Rotation) plots are generated when new 'Level 0' (LZ) files are downloaded. They are created using 5-min averaged parameters that are further averaged to form 1-hour averages.

A paper describing the analysis technique is available.