Preprint version. Journal of Geophysical Research, Volume 110, Issue B02207, February 10, 2004, pages 1-2.
NOTE: At the time of publication, the author Scott Johnston was not yet affiliated with Cal Poly.
The definitive version is available at https://doi.org/10.1029/2004JB003490.
An edited version of this paper was published by AGU. Further reproduction or electronic distribution is not permitted.