ACTIVE REGIONS OBSERVED IN EXTREME-ULTRAVIOLET LIGHT BY THE CORONAL DIAGNOSTIC SPECTROMETER ON SOHO

We present observations of five active regions made by the Coronal Dia gnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory ( SOHO). CDS observes the Sun in the extreme ultraviolet range 150-780 A ngstrom. Examples of active region loops seen in spectral lines emitte d at various temperatures are shown, Several classes of loops are iden tified: those that are seen in all temperatures up to 2 x 10(6) K; loo ps seen at 10(6) K but not reaching 1.6 x 10(6) K; those at temperatur es 2-4 x 10(5) K and occasionally at 6 x 10(6) K but not reaching 10(6 ) K. An increasing loop size with temperature and the relationship bet ween the cool and hot structures is discussed. CDS observations reveal the existence of loops and other unresolved structures in active regi ons at temperatures between 1.5-4 x 10(5) K, which do not have counter parts in lines emitted above 8 x 10(5) K. Bright compact sources only seen in the transition region lines are investigated. These sources ca n have lifetimes of up to several days and are located in the vicinity of sunspots, We study the variability of active region sources on tim e scales from 30 sec to several days. We find oscillatory behaviour of He I and O V line intensities in an active region on time scales of 5 -10 min.