The Effects of Active Regions on Solar Spectral Variability: Implications for the Sun’s
influence on climate
Dora Preminger [dora.preminger@csun.edu], Gary Chapman, and Angela Cookson, San
Fernando Observatory, California State University, Northridge
We use photometric parameters from the San Fernando Observatory’s solar data archive
to model the Total Solar Irradiance (TSI) for two full solar cycles. Our results have
implications for the ways in which the Sun might affect Earth’s climate. The TSI, incident at
the top of the Earth’s atmosphere, is about 1365 Wm-2 and varies from solar minimum to
solar maximum by an amount ΔTSI of order 1 Wm-2. Our TSI model, which successfully
reconstructs observed TSI values, implies that, to a first approximation, ΔTSI is caused by
solar active regions and can be attributed to two components: the change in the visible
continuum radiation from the photosphere and the change in the spectral line blanketing from
the chromosphere. The visible continuum component of TSI, which can pass through the
Earth’s atmosphere and warm the ground and oceans directly, changes by a small fraction, of
order 0.01%, from solar minimum to solar maximum, and its variability is anti-correlated
with the solar cycle. If high solar activity is associated with high global temperatures, then
this component cannot be the cause. The energy in chromospheric spectral lines, which are
mostly concentrated at ultraviolet wavelengths, changes by an amount of order +ΔTSI from
solar minimum to solar maximum. Ultraviolet radiation is absorbed in the Earth’s
atmosphere and could constitute a different mechanism for driving climate change that would
be positively correlated with solar activity.