Estimation of Magnetic Field Strength in the Turbulent Warm Ionized
  Medium
  We studied Faraday rotation measure (RM) in turbulent media with the rms Mach
number of unity, using isothermal, magnetohydrodynamic turbulence simulations.
Four cases with different values of initial plasma beta were considered. Our
main findings are as follows. (1) There is no strong correlation between the
fluctuations of magnetic field strength and gas density. So the magnetic field
strength estimated with RM/DM (DM is the dispersion measure) correctly
represents the true mean strength of the magnetic field along the line of
sight. (2) The frequency distribution of RMs is well fitted to the Gaussian. In
addition, there is a good relation between the width of the distribution of
RM/$\bar{\rm RM}$ ($\bar{\rm RM}$ is the average value of RMs) and the strength
of the regular field along the line of sight; the width is narrower, if the
field strength is stronger. We discussed the implications of our findings in
the warm ionized medium where the Mach number of turbulent motions is around
unity.
