Source of sunspot supersonic downflows. (a) An EUVI 304 Å image showing the condensation-related dip region. The solar disk and the FOV of these images are shown as the white circle and the green rectangle, respectively. The two arrows indicate the thickness for a condensation clump. (a1) and (a2) Examples of condensation identification in the white box of panel a at two different times. The green dots denote the pixels where condensation takes place. (b) Time variation of the condensation mass (black diamonds) and condensation rate (red triangles) during the period of 16:46−19:26 UT (IRIS Raster 5).