Reconstruction of solar irradiance variations for use in studies of global climate change : application of recent SoHO observations with historic data from the Greenwich Observatory

Abstract

In this thesis, I develop a composite of observations from a variety of datasets that is homogeneous in both sunspot area and sunspot position.

I use this continuous and homogeneous dataset to investigate known long-term variations in sunspot latitudes and area, and relate these to variations in the open magnetic flux of the Sun, as recently discovered from analysis of historical records of geomagnetic activity.  The dataset is also readily applicable to the reconstruction of the darkening effect of sunspots on TSI, but reconstruction of the brightening effect of faculae is more challenging.  I investigate the implications for facular brightening if the correlation of open flux with TSI were to apply on century as well as decadal timescales.  This work has implications for paleoclimate studies which use cosmogenic isotopes as an indicator of solar variability.

Lastly, I employ recent SoHO observations of the contrast of flux tubes such as faculae in conjunction with the composite sunspot data series to model the variation in facular brightening over the past century, and using inferred variations in the solar magnetic field.  This procedure allows the brightening by active region faculae around sunspots to be reconstructed with some certainty, but still requires assumptions to be made about the behaviour of network faculae and any other small flux tubes outside active regions.  Three models of TSI are developed, based upon three assumptions.  These models are compared to the standard models and satellite measurements of TSI, and the possible implications for the detection and attribution of the various factors, which have influenced global climate change over the past 150 years are discussed.

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