  It is well-known that extreme ultraviolet emission emitted at the solar
surface is absorbed by overlying cool plasma. Especially in active regions dark
lanes in EUV images suggest that much of the surface activity is obscured.
Simultaneous observations from IRIS, consisting of UV spectra and slit-jaw
images give vital information with sub-arcsecond spatial resolution on the
dynamics of jets not seen in EUV images. We studied a series of small jets from
recently formed bipole pairs beside the trailing spot of active region 11991,
which occurred on 2014 March 5 from 15:02:21 UT to 17:04:07 UT. There were
collimated outflows with bright roots in the SJI 1400 {\AA} (transition region)
and 2796 {\AA} (upper chromosphere) that were mostly not seen in AIA 304 {\AA}
(transition region) and AIA 171 \AA\ (lower corona) images. The Si IV spectra
show strong blue-wing but no red-wing enhancements in the line profiles of the
ejecta for all recurrent jets indicating outward flows without twists. We see
two types of Mg II line profiles produced by the jets spires: reversed and
non-reversed. Mg II lines remain optically thick but turn into optically thin
in the highly Doppler shifted wings.The energy flux contained in each recurrent
jet is estimated using a velocity differential emission measure technique which
measures the emitting power of the plasma as a function of line-of-sight
velocity. We found that all the recurrent jets release similar energy (10$^8$
erg cm$^{-2}$ s$^{-1}$ ) toward the corona and the downward component is less
than 3\%.
