We have discovered a way to calculate solar wind velocities using the LECP ion channels. We require the angular dependent count rate at a particular energy and the spectrum in order to calculate a solar wind velocity. During quiet times the data must be averaged into long term bins. We have used averaging that varies from 1 day to 26 days depending on the level of activity present. Some of the ion channels do not operate in anticoincidence and therefore have high cosmic background rates which must be subtracted from foreground solar wind ions to determine their flow. This is possible since we assume isotropy for cosmic rays and therefore can subtract the same number of counts from each sector. During the most quiet times, we can calibrate this rate to a rate in a high energy channel that only counts cosmic rays so that a linear correlation is calculated between the cosmic ray channel and the lower energy ion channels. We frequently use a 1 MeV channel called Channel 1 which does operate in anticoincidence and has a very low cosmic ray background rate. However, this also has a calculated background which is subtracted during quiet times.
We have calculated the velocity at Voyagers 1 and 2 for periods during 1980, 1991, and 1992 and the majority of the period 1980-1994 for Voyager 1 although substantial gaps in coverage still exist. As we are working at the boundary of the capability of LECP, we will continue to push our limits to obtain Voyager 1 numbers and to improve our resolution from 26 day averaging to 5 day and even 1 day where conditions permit. Since Voyager 1 speeds are not available after 1980 from the PLS detector, we will focus our efforts on Voyager 1, that spacecraft most likely to cross the Termination Shock of the heliosphere first.
We have included a tutorial that outlines our methodology, and are working on a paper to be submitted to the Journal of Geophysical Research as a follow up to our 1998 paper on the subject. This work has evolved from our work on Jupiter's magnetodisk using both the Voyager LECP and Galileo EPD detectors. Please send your suggestions to mark_kane (note the underscore which may not be visible if you set your browser to underline links but it is in the link address) (e-mail: mark_kane@yahoo.com) as well as requests for data or graphics.