Solar Chromospheric Flares: Observations in Ly-alpha and H-alpha and Radiative Hydrodynamic Simulations

This thesis is divided into two main parts: a multi-wavelength observational study of solar flares, focusing mainly in the chromosphere in Ly-alpha and H-alpha, and an application of a radiative transfer code and a radiative hydrodynamic code, to compare the results obtained by observations with the simulated ones. The Ly-alpha emission is a very interesting line because it is a natural tracer of the solar activity in the chromosphere. The Transition Region And Coronal Explorer satellite observed a small number of flares in the Ly-alpha passband, but apart from this, these events have not often been observed in this strong chromospheric line. Because TRACE has a broad Ly-alpha channel, in order to estimate the ``pure'' Ly-alpha emission, we had to apply an empirical correction. We found that there is a reasonable coverage in TRACE 1216 A and the TRACE 1600 A for two different flares: on 8 September 1999 and on 28 February 1999. Studying them we estimated, for the first time, the pure Ly-alpha flare signature, being on the order of 10^{25} erg/s at the flare peak. The study of the first flare gave us the possibility to calculate the electron energy budget using the X-ray data from Yohkoh/HXT in the context of the collisional thick target model, finding that the Ly-