Correlated variations of solar EUV line emissions

Spectral measurements of the AEROS satellites were used to check Hinteregger's (Hinteregger, H.E. The extreme ultraviolet solar spectrum and its variation during a solar cycle. Ann. Geophys. 26, 547, 1970) idea that monitoring two suitably chosen EUV lines might well allow assessing the aeronomical effects of solar EUV. Representative daily intensity values have been determined for 25 most important EUV emission lines. Cross correlations calculated for each of these with three classical activity indices (RZ, F10.7 and Ap) ended-up with mostly insignificant correlation values. Correlations were also determined for all couples of the 25 emission lines themselves. In a two-dimensional field there appeared two distinct districts with significant correlations amongst all lines therein, one district with mainly chromospheric emissions, the other one with those of the corona. Our results may confirm Hinteregger's idea. It is concluded that an extremely simple spectrometer monitoring just two lines might be most helpful to fill the gaps between more ambitious solar EUV-missions.