  To better understand a preferred magnetic field configuration and its
evolution during Coronal Mass Ejection events, we investigated the spatial and
temporal evolution of photospheric magnetic fields in the active region NOAA
9236 that produced eight flare-associated CMEs during the time period of 2000
November 23-26. The time variations of the total magnetic helicity injection
rate and the total unsigned magnetic flux are determined and examined not only
in the entire active region but also in some local regions such as the main
sunspots and the CME-associated flaring regions using SOHO/MDI magnetogram
data. As a result, we found that: (1) in the sunspots, a large amount of
postive (right-handed) magnetic helicity was injected during most of the
examined time period, (2) in the flare region, there was a continuous injection
of negative (left-handed) magnetic helicity during the entire period,
accompanied by a large increase of the unsigned magnetic flux, and (3) the
flaring regions were mainly composed of emerging bipoles of magnetic fragments
in which magnetic field lines have substantially favorable conditions for
making reconnection with large-scale, overlying, and oppositely directed
magnetic field lines connecting the main sunspots. These observational findings
can also be well explained by some MHD numerical simulations for CME initiation
(e.g., reconnection-favored emerging flux models). We therefore conclude that
reconnection-favored magnetic fields in the flaring emerging flux regions play
a crucial role in producing the multiple flare-associated CMEs in NOAA 9236.
