Conférence de William Ball, Imperial College London.
Résumé
Absorption of solar ultraviolet (UV) radiation by ozone is the main source of heating in the stratosphere, affecting the chemistry, temperature and dynamics of the atmosphere. Here, I will (1) present a revised and updated SSI dataset using the SATIRE-S model, in the context of other irradiance models and observations, and (2) investigate the limits in our knowledge of how SSI may vary over the solar cycle (SC) by using stratospheric ozone observations and Bayesian inference. The new SATIRE-S SSI dataset spans 1974 to 2009. I compare SATIRE-S with the NRLSSI model and SORCE/SOLSTICE observations. SATIRE-S and NRLSSI show similar SC changes below 250 nm. However, SATIRE-S show almost double the change in flux as NRLSSI between 250 and 310 nm, but less than half that of SORCE/SOLSTICE. These various UV changes lead to different ozone responses in the stratosphere. Instead of just comparing the ozone response to these different SSI datasets with ozone observations, I pose the question: Can the observed SC change in stratospheric ozone constrain the allowed range of solar UV changes? To answer this, I first show that the response of equatorial stratospheric ozone to SC changes in UV can be estimated using a simple linear approximation. This then allows a Bayesian formalism to show that one cannot distinguish between different SSI datasets using current estimates of ozone changes. The Bayesian approach presented here could be developed to investigate other datasets and provide a better understanding of both variations in SSI and the atmospheric response to it.
Présentée par le Groupe Astronomie et astrophysique du Département de physique de l'Université de Montréal. Cette conférence est destinée à des spécialistes dans le domaine de l'astrophysique et sera donnée en anglais.
