The 530.3 nm corona irradiance from 1939 to 2001

Abstract

We introduce the coronal index of solar activity (CI) for the period 1939–2001. The CI represents the total irradiance for the Sun as a star in the 530.3 nm coronal emission line as observed with ground-based coronagraphs over the world. There have been found long-term variations in the values of CI (monotonously increasing from 1947 to 1996), cycle variations (11 years), intermediate variability (from 3 months to 5 years), and rotational rate of 27.3 days (with some subsidiary peaks ranging from 25 to 30 days). Comparison between the CI and total magnetic flux showed a good relationship in 1976–1999. This relation was used to derive the magnetic flux before 1976 back to 1939 when the green corona (530.3 nm, the Fe XIV) began to be observed. Similar comparisons have been made between the CI and total solar irradiance, enabling us to extrapolate the values of total solar irradiance from 1986 back to 1939. It follows that density, temperature, magnetic flux and total solar irradiance increased in the observational period from 1946 to 1996 of cycle maxima. The last solar cycle 23 exhibited a drop-off in irradiance about a third in comparison with the solar cycle 22.