J.-D. F. Bartoe

Transition zone flows observed in a coronal hole on the solar disk

A rocket flight of the NRL High Resolution Telescope and Spectrograph (HRTS) was performed to obtain ultraviolet spectra of a well-defined coronal hole on the solar system. Observed emission lines included strong transition zone lines of C IV at 1548 and 1550 A, strong chromospheric lines of C I near 1560 A, and chromospheric lines of Fe (II) at 1563 A. Continuum radiation formed in the temperature minimum was also recorded. The cumulative histogram of the C IV velocities in the coronal hole shows an average Doppler shift of 2 km/sec to the red (downflow) with 26 percent of the profiles having blueshifts (outflows) compared to 7 percent in the quiet sun. The present observations have the advantages of higher spatial resolution and a nearly absolute wavelength scale determined from narrow chromospheric lines of Si I with an accuracy of about 1 km/sec. The nonthermal velocities, derived from the C IV line widths, are only marginally larger inside the coronal hole than those in the quiet sun, thus indicating that the magnitude of small-scale motions, which may represent energy available for coronal heating and solar wind acceleration, is equal in the two regions. 21 refs.

Plasma motions in an emerging flux region. [in solar atmosphere]

Ultraviolet spectra of C IV show large nonthermal broadening in an area of emerging flux. These nonthermal motions are observed at a very early stage of reconnecting field lines. The spectra can be traced to small, rapidly changing surge or filament-like features which are seen in the center, blue, and red wing of H-alpha. They seem to have the characteristics of macrospicules or explosive events. They are precursors of the reconnection process. Plasma turbulence and/or plasma waves in the reconnecting plasma may cause the broad C IV line profiles. The activity in the transition zone precedes the formation of a bright chromospheric loop system. 19 references.

Outflows and ejections in the solar transition zone

Fourteen examples of blue-shifted emission patterns detected in C IV profiles are studied. Time series images of C IV transition zone intensities and velocities, obtained with a high resolution telescope and spectrograph, are described and analyzed. It is observed that three of the blue-shifts are produced by wide-profile events, and 11 of the blue-shifted events, six of which are associated with the chromospheric network, are characterized by near-Gaussian profiles. The analysis reveals that the blue-shifted profiles are more complex than the red-shifted profiles, the blue-shifted events are highly transient, and the spatial extent of the blue-shift patterns is smaller than that of the red-shift patterns. 13 references.

CO fluorescence in the extreme-ultraviolet solar spectrum

Emission lines in the fourth positive system of CO have been identified in the extreme-ultraviolet solar spectrum 1540-1660 A. These lines are excited by the C IV transition-zone lines at 1548 and 1551 A. They are strong in the spectrum of a sunspot and in parts of the adjacent active region. Some of them appear as weak, broad emission features in the quiet sun.