AAS 200th meeting, Albuquerque, NM, June 2002
Session 38. Solar Photosphere, Chromosphere and Transition Region
Display, Tuesday, June 4, 2002, 10:00am-6:30pm, SW Exhibit Hall

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[38.11] The Structure of the Lower Solar Transition Region

G. A. Doschek, J. T. Mariska (E. O. Hulburt Center for Space Research, NRL), S. Akiyama (George Mason University/NRL)

Recent high-spatial resolution monochromatic images obtained from the SUMER spectrometer on SOHO have shown that the lower transition region (~ 2 x 104 - 2 x 105 K) is composed of small loops and knots of emission (seen on the disk), and thread-like structures (seen above the limb) (Feldman, Widing, & Warren, ApJ, 522, 1133 (1999)). The structures seen in images of different spectral lines formed at significantly different electron temperatures look quite similar. However, because the temperatures are different, the emitting plasma cannot be the same for the different images. What is the physical relationship between lower transition region structures that appear in lines formed at different temperatures? The answer to this question can begin to be addressed by examining SUMER spectra of lower transition region lines formed at different temperatures that appear on the same SUMER exposures. In this case the spatial region on the Sun viewed in both spectral lines is precisely the same, and both lines are recorded simultaneously. The intensity relationship between lines of Si IV (6.3 x 104 K) and O IV (1.3 x 105 K) for such spectra has already been discussed by Doschek & Mariska (ApJ, 560, 420 (2001)), and a strong correlation between Si IV and O IV intensities was found. We will discuss an extension of this work to line groups of, (1) O II, O III (3 x 104, 9.0 x 104 K), (2) C IV, S V, O IV (1 x 105, 1.6 x 105, 1.6 x 105 K), and (3) N IV, O V (1.4 x 105, 2.5 x 105 K). The O II, O III comparison does not show the strong correlation found for higher temperature lines, indicating that chromospheric structures are significantly different from lower transition region structures. The S V and O IV temperature regions strongly overlap but are not identical. Nevertheless, the intensity correlation is quite high. This work was supported by NASA solar physics Guest Investigator Grant S137816.

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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.