Peter Foukal/Heliophysics, Inc.
Facular
Studies to Understand
Solar Dynamo and Irradiance Behavior.
Digitization
of the archival plates at Mt Wilson and Kodaikanal Observatories now
provides a continuous record of white light faculae since 1907. We
propose to measure facular areas to investigate a relation reported
between the (facula/ spot) area ratio at the onset of a solar cycle,
and that cycle’s peak amplitude. This relation, if verified, suggests a
predictively useful and dynamically interesting connection between the
spatial structure of photospheric magnetic fields, and solar dynamo
efficiency.
These recent digitizations also provide extended time series of Ca K
plage areas. We have used these to reconstruct solar UV flux variation,
pointing out that it correlates only weakly with 20th century global
temperature, thus calling into question UV driving of global warming.
Reconstruction of total solar irradiance (TSI) variation poses a
tougher challenge, because the contributions of spots and faculae tend
to cancel so they must be known accurately to provide confidence in the
calculation of their small difference . We propose to apply the
extended plage area record, together with broad band facular contrasts
from the balloon - borne Solar Bolometric Imager, to improve TSI
reconstruction back to 1907.
We also propose to extend this irradiance reconstruction yet further
back in time using recent modeling of active region evolution, which
indicates that plage area variations can be reconstructed usefully from
spot and white light facular areas. To do this, we will develop a
simplified kinematical model to improve irradiance reconstructions to
the beginning of the Royal Greenwich Observatory records in 1874.
Finally, we propose to investigate whether the unusually low TSI values
measured during the present sunspot minimum might be explained by
declining numbers of polar faculae. If not, new TSI variation
mechanisms not associated with photospheric magnetism might be
required, with profound implications for Sun - climate driving.
