  Recent high-resolution observations reveal that subarcsecond bright dots
(BDs) with sub-minute lifetimes appears ubiquitously in the transition region
(TR) above sunspot penumbra. The presence of penumbral micro-jets (PMJs) in the
chromosphere have also been reported earlier. It was proposed that both the
PMJs and BDs are formed due to magnetic reconnection process and may play an
important role in heating of the penumbra. Using simultaneous observation of
the chromosphere from the Solar Optical Telescope (SOT) aboard Hinode and the
TR from the Interface Region Imaging Spectrograph (IRIS), we study the dynamics
of BDs and their relation with PMJs. We find two types of BDs, one which is
related to PMJs and the others which do not show any visible dynamics in the
SOT Ca II H images. From a statistical analysis we show that these two types
have different properties. The BDs which are related to PMJs always appear at
the top of the PMJs, the vast majority of which show inward motion and
originate before the generation of the PMJs. These results may indicate that
the reconnection occurs at the lower coronal/TR height and initiates PMJs at
the chromosphere. This formation mechanism is in contrast with the currently
believed formation of PMJs by reconnection in the (upper) photosphere between
differently inclined fields.
