We report on an investigation of the microwave enhancement and its
variability in the elephant trunk coronal hole observed during the Whole
Sun Month campaign (August 10 - September 09, 1996).  The microwave images
from the Nobeyama Radioheliograph were compared with magnetograms and EUV
images obtained simultaneously by the Michelson Doppler Imager (MDI) and
the Extreme Ultraviolet Imaging Telescope (EIT) on board the SOHO
spacecraft.  The combined data set allowed us to understand the detailed
structure of the microwave enhancement in the spatial and temporal
domains.  We find that the radio enhancement is closely associated with
the enhanced unipolar magnetic regions underlying the coronal hole.  The
radio enhancement consists of a smooth component originating from network
cell interiors and a compact component associated with network magnetic
elements.  When a minority polarity is present near a majority polarity
element, within the coronal hole, the resulting mixed polarity region is
associated with a bright-point-like emission in coronal EUV lines such as
the Fe XII 195 angstrom.  These coronal bright points are also observed
distinctly in the EIT 304 angstrom band, but not in microwaves.  On the
other hand, the lower temperature line emission (304 angstrom) and the
microwave enhancement are associated with the unipolar magnetic flux
elements in the network.  We found strong time variability of the radio
enhancement over multiple time scales, consistent with the initial results
obtained by SOHO instruments.  The microwave enhancement is most probably
due to temperature enhancement in the chromosphere and may be related to
the origin of solar wind.