The definition of magnetosonic speed (Vms) used in this database
is not the most generic definition thereof.  The generic definition of
Vms (for "fast mode") is given by (e.g., Merka et al, JGR, Feb 2003)

Vms**2 = 0.5 * {Va**2 + Vs**2 + [(Va**2 + Vs**2)**2 -
4 * Va**2 * Vs**2 * (cos (theta))**2]**0.5}

(Note to reader: For "slow mode," replace the "+" immediately preceding 
the [...] term in the above expression with a "-".)

In this expression, Va and Vs are the Alfven and sound speeds,
and theta is the angle between the wave propagation direction and
the ambient magnetic field.  Under the usual assumption that the
wave propagation direction and the solar wind flow direction are
nearly coaligned, theta is typically taken to be the angle between
the magnetic field vector and the solar wind flow vector,
cos (theta) = (V dot B) / |V|*|B|.

In this context, it clear that this database's "magnetosonic speed" is
actually the magnetosonic speed for the fast-mode wave for the case
of magnetic field vector normal to the solar wind flow vector.

Users may compute "true" magnetosonic speed from the parameters
contained in the data records of this database.

JHK, 6/2/2005