Velocity gradients in the chromosphere-corona transition region

Velocity data obtained from Doppler shifts of EUV spectral lines observed with the High Resolution Telescope and Spectrograph flown on Spacelab II are analyzed to determine the properties of the mean velocities V-bar and its spatial variance V(sigma), for chromospheric and transition region lines. The lines studied include the ions O I, C I, Fe II, C II, Si III, Si IV, and C IV. The constancy of V(sigma) from center to limb together with a systematic maximum redshift in V-bar in central disk regions is interpreted to mean that the plasma flow is divergent from the tops of closed field lines and that the cool plasma more or less fills the magnetic loops from which most of the radiation originates. The same is true of the hotter plasma. It is suggested that the crossfield component of Delta T is large and that the alternation from cool loops to hot loops occurs on spatial scales much less than 1 arcsec.