  One of the key problems in star formation research is to determine the role
of magnetic fields. Starting from the atomic inter-cloud medium (ICM) which has
density nH ~ 1 per cubic cm, gas must accumulate from a volume several hundred
pc across in order to form a typical molecular cloud. Star formation usually
occurs in cloud cores, which have linear sizes below 1 pc and densities nH2 >
10^5 per cubic cm. With current technologies, it is hard to probe magnetic
fields at scales lying between the accumulation length and the size of cloud
cores, a range corresponds to many levels of turbulent eddy cascade, and many
orders of magnitude of density amplification. For field directions detected
from the two extremes, however, we show here that a significant correlation is
found. Comparing this result with molecular cloud simulations, only the
sub-Alfvenic cases result in field orientations consistent with our
observations.
