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It is well-known that extreme ultraviolet emission emitted at the solarsurface is absorbed by overlying cool plasma. Especially in active regions darklanes in EUV images suggest that much of the surface activity is obscured.Simultaneous observations from IRIS, consisting of UV spectra and slit-jawimages give vital information with sub-arcsecond spatial resolution on thedynamics of jets not seen in EUV images. We studied a series of small jets fromrecently 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 werecollimated 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 spectrashow strong blue-wing but no red-wing enhancements in the line profiles of theejecta for all recurrent jets indicating outward flows without twists. We seetwo types of Mg II line profiles produced by the jets spires: reversed andnon-reversed. Mg II lines remain optically thick but turn into optically thinin the highly Doppler shifted wings.The energy flux contained in each recurrentjet is estimated using a velocity differential emission measure technique whichmeasures the emitting power of the plasma as a function of line-of-sightvelocity. 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 lessthan 3\%.

Undercover EUV Solar Jets Observed by the Interface Region Imaging Spectrograph