Abstracts submitted by Thierry Dudok de Wit

Multispectral analysis of EIT images: linking temperature to morphology

T. Dudok de Wit [1] and F. Auchère [2]

[1] LPCE, CNRS and University of Orléans, Orléans; [2] IAS, CNRS and Paris Sud University, Orsay

EIT images in different wavelengths have frequently been studied with the aim of inferring information about emission temperatures and thereby distinguish different solar structures. We consider a more empirical approach to this problem, using blind source separation methods.

The morphology of solar structures changes with the wavelength of observation; we explore the possibility of using this property to separate different solar structures from a linear combination of EIT images. A set of statistically independent ``source'' images is built from the original EIT images, using independent component analysis. These source images show more contrast than the original ones and ease the characterisation of morphological structures. A comparison with the differential emission measure shows that each source image also isolates structures with specific emission temperatures. Such a decomposition is well suited for scanning through multispectral solar images and identifying structures of interest.
Can the total solar irradiance be reconstructed from solar activity proxies ?

T. Dudok de Wit [1], M. Kretzschmar [2], J. Lilensten [3], P.-O. Amblard [4], S. Moussaoui [5], J. Aboudarham [6], F. Auchère [7]

[1] LPCE, Orléans, [2] ROB, Brssels, [3] LPG, Grenoble, [4] GIPSAlab, Grenoble, [5] IRCCYN, Nantes, [6] LESIA, Paris, [7] IAS, Orsay

Understanding how the Total Solar Irradiance (TSI) is related to solar activity is not only important for predicting its value in the past, but also for understanding what causes its variability. It is today widely accepted that the variability of the TSI is mainly governed by the presence of thermal regions (plages and faculae) and a deficit caused by sunspots. Attempts in modelling the TSI from these two contributions have been quite succesful, but significant discrepancies persist.

Instead of answering the usual question of how the TSI can be reconstructed from solar proxies, we want to know if and to what degree the TSI can actually be reconstructed from solar proxies. Using concepts from infomation theory, we estimate how much information the TSI shares with 29 years of various proxies such as the sunspot number, the MgII, CaK and HeI indices, the daily sunspot area and more. From this, we determine: 1) which quantities are best for reconstructing the TSI, and 2) if there are (linear or nonlinear) combinations of proxies from which the TSI can be reconstructed.

The results first show that no single combination of proxies can fully reproduce the variability of the TSI, whose dynamics contains a contribution that isn't contained in any of the proxies. Secondly, they clearly reveal the importance of regions of intense magnetic field (e.g. Mount Wilson Sunspot Index, and Optical Flare Index) for fitting short time scales and of more thermal regions (Lyman-a, CaK, coronal index) for reproducing long (>> 27 days) scales.