Multiple flow velocities in the transition region

Abstract

Observations with the High Resolution Telescope and Spectrograph (HRTS) of the C IV lines at 1550 A above sunspots reveal the coexistence of several distinct high velocity gas components within the instrument resolution element of 1 x 1 arcsec. A further investigation of the HRTS material demonstrates that such multiple gas velocities are not restricted to the temperature region around 100,000 K, where the C IV lines are formed, but that the gas flows with essentially unchanged speed through all temperature layers from 250,000 K to 10,000 K. Furthermore, the phenomenon is not restricted to sunspots, but occurs also in other solar regions, often most easily distinguished in active regions. The characteristics of the velocity fields are described. The mass fluxes are analyzed, and the requirements they place on the resolving power of future space instruments are discussed.