Observations with the Interface Region Imaging Spectrograph ( IRIS ) have revealed numerous sub-arcsecond bright dots in the transition region above sunspots .
These bright dots are seen in the 1400Å and 1330Å slit-jaw images .
They are clearly present in all sunspots we investigated , mostly in the penumbrae , but also occasionally in some umbrae and light bridges .
The bright dots in the penumbrae typically appear slightly elongated , with the two dimensions being 300–600 km and 250–450 km , respectively .
The long sides of these dots are often nearly parallel to the bright filamentary structures in the penumbrae but sometimes clearly deviate from the radial direction .
Their lifetimes are mostly less than one minute , although some dots last for a few minutes or even longer .
Their intensities are often a few times stronger than the intensities of the surrounding environment in the slit-jaw images .
About half of the bright dots show apparent movement with speeds of \sim 10–40 km s ^ { -1 } in the radial direction .
Spectra of a few bright dots were obtained and the Si iv 1402.77Å line profiles in these dots are significantly broadened .
The line intensity can be enhanced by one to two orders of magnitude .
Some relatively bright and long-lasting dots are also observed in several passbands of the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory , and they appear to be located at the bases of loop-like structures .
Many of these bright dots are likely associated with small-scale energy release events at the transition region footpoints of magnetic loops .