Atomic physics for atmospheric composition measurements

The atomic physics relevant to the interpretation of solar spectra produced by plasmas at temperatures greater than or similar to 10(5) K are discusse d. Methods for determining relative abundance ratios are presented and exam ples provided from the Coronal Diagnostic Spectrometer on board SOHO. In pa rticular, the Fe/Si ratio in the corona is found to be close to photospheri c; the Mg/Ne ratio in the transition region is found to vary by an order of magnitude in different solar features. The Mg/Ne ratios in supergranule ce ll centres and the network are separated for the first time, although no si gnificant differences are found.