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C.-Y. Lee, H. Wang, J. Chae (Big Bear Solar Observatory)
The Littrow spectrograph in the Big Bear Solar Observatory (BBSO) is an unique grating system which can produce a 4-dimensional (x,y,\lambda,t) data array. We are mainly interested in studying H\alpha fine features like upflow events, spicules/fibrils, and dark grains by means of constructed spectroheligrams. We have found from upflow events: (1) The typical profile indicates a spectral character in which absorption is only observed in the blue wing. (2) The line-center optical thickness is lower than that of spicules. (3) The motion has no receding phase as seen in H\alpha as shown by Doppler signals. The lifetime, size, and velocity of upflow events are found to be 1.4 minutes, 2.5 arcsec (FWHM), and 15 km s-1 respectively. Dark grains may be considered to be the least energetic upflow events in the sense that its lifetime and size are about half that of upflow events. The total birthrate is estimated to be 200 s-1, which is about one third of that of explosive events. The association of the magnetic origin of explosive events has been reported by a previous study on the use of BBSO/magnetograms and SOHO/SUMER UV images. The electron temperature (104 K) and density (1010 cm-3) of upflow events can easily be found. The global particle and kinetic energy flux are determined to be 1015 cm-2 s-1 and 105 ergs cm-2 s-1 respectively. Judged by the favorable amount of particle flux, we propose a scenario in that the predominant downflow observed in UV is due to hot and diffusive returning material of H\alpha upflow events. Comparisons with TRACE/EUV images are in process.
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