Relation of transition region blinkers to the low chromosphere

Abstract

We investigated the coupling between the low chromosphere, lower and upper transition region through the study of blinkers. Blinkers are extreme ultraviolet (EUV) small-scale transient brightenings best detected in transition region lines showing an intensity enhancement on the 60−100% level on average. We analysed time-series spectra of the C II 1037 A (2−4 × 10 4 K, lower transition region) and O VI 1038 A (3×10 5 K, upper transition region) lines, as well as the C I continuum at 1042 A formed about 1 Mm above the solar surface, obtained with the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) spectrometer on SOHO. Blinkers detected in C II and O VI have similar enhancement levels. We found a modest space-time overlap between blinkers in the two lines and a small correlation between C II or O VI blinkers and the corresponding light curve in the chromospheric continuum. This suggests a relation of EUV blinkers to the chromosphere, which could support the idea that blinkers are the consequence of granular collisions. The average duration of O VI blinkers amounts to 10.0 min and of C II blinkers to 6.7 min.