Climate of an Earth-like extrasolar planet orbiting a K-type star
Résumé
For terrestrial planets the energy provided by the central star is usually the main energy source.The total amount of energy received at the top of the planetary atmosphere depends on the stellar luminosity, hence stellar type, and the planet to star distance. The influence of the total amount of energy, the spectral distribution of the stellar energy and the concentration of some radiative species on global mean atmospheric and surface temperatures has been investigated with one-dimensional (1D) radiative convective models and with a three-dimensional (3D) climate model for the special case of Gliese 581d, for example. To improve the understanding of the interaction between stellar radiation characteristics, atmospheric dynamics and local planetary conditions, we make use of the 3D general circulation model EMAC (ECHAM/MESSy Atmospheric Chemistry model, Jöckel et al., 2006), which has been developed for Earth climate studies, to calculate the climate of an Earth-like extrasolar planet around a K-type star. In the EMAC-FUB configuration the model is run with a high spectral resolution scheme (Nissen et al., 2007) in the stellar radiative transfer, which is important for studying the influence of the stellar spectral distribution. As a first step we investigate the influence of a K-type stellar spectral energy distribution upon atmospheric dynamics, focusing on the stratosphere, since the radiation has its largest impact here. In a second step, we couple a mixed layer ocean to the atmosphere, to investigate the influence of the surface properties upon surface temperatures, e.g. the change in surface albedo due to melting surface ice. Since the total stellar irradiance depends on the planet to star distance, we consider in a third scenario consistent values for the stellar radiation and the length of year. The response of the surface temperatures and other atmospheric properties is analysed. The 3D model results are compared to those of a 1D radiative-convective model to evaluate the importance of atmospheric dynamics and surface properties for the global mean climate state of Earth-like extrasolar planets yielding information about the potential usability of 1D modelling results in view of the search for especially habitable extrasolar planets.