[Observation and diagnostic of ultraviolet spectra in the solar transition region]

The solar transition region is the thin atmosphere layer between the chromosphere and corona. Although the thickness of the solar transition region is only several hundred kilometers, the parameters of the plasma change dramatically. The temperature increases from 10(4) to 10(6) K and the density drops from 10(10) to 10(8) cm(-3). The emission of the solar transition region is generally of optical-thin far-ultraviolet (FUV) spectral lines, extreme-ultraviolet (EUV) spectral lines and background continuous spectral lines. However, the traditional ground-based observations can not be made for FUV/EUV lines, owing to their strong absorption by ozone and other molecules in the earth's atmosphere. Thus, FUV/EUV lines only can be obtained with space-based observations. In recent decades, the successful launch of space-borne instruments opened a new era of the research for the solar transition region. The present paper reviews the observation history of ultraviolet spectra in the solar transition region and some kinds of space-borne instruments, especially several important spectrometers in recent ten years. At the same time, the diagnostics of the emissivity, electron density and electronic temperature of ultraviolet spectra in the solar transition region are expounded in detail. The shape of ultraviolet line is discussed and several important parameters with physical significance are showed using SOHO/SUMER spectrometer.