The study of atmospheric circulation and climate began hundreds of years ago with attempts to understand the processes that determine the local climate on Earth and predict it for human needs. Today, we can represent the complex global circulation of Earth with extraordinary detail, through numerical simulations. As theories of Earth’s general circulation became more sophisticated, the characterization of the other Solar-System planets by spacecraft, demonstrated that the climate and circulation of other atmospheres differ, sometimes radically, from that of Earth. Nevertheless, since the law of physics have to be the same in all our universe, it is safe to assume that, using some universal equations, is possible to reproduce any planetary atmosphere circulation with good approximations. Extrasolar planets, occupying a far greater range of physical and orbital characteristics than planets in our Solar System, likewise plausibly span an even greater diversity of circulation and climate regimes. This diversity provides a motivation for extending the theory of atmospheric circulation beyond our terrestrial experience. Particular attention is given to terrestrial planets, in the light of the fact that liquid water and life could be present on them. This brought several authors to study the boundaries of the so called ‘habitable zone’, i.e. the area around a star in which the planet has to orbit in order to receive the amount of radiant energy necessary to sustain liquid water on its surface . Although this definition of habitable zone seems to be reasonable, it is very partial and simplistic, because liquid water could exist in a wide ranges of pressure and temperatures (i.e. above 300 deg C and 107 millibars) or conditions (beneath ice covered surface), so it’s hard to unambiguously define the habitable zone boundaries. Moreover, a planet inside the habitable zone is not necessarily habitable. However, even if the habitability criteria are without doubt one of the most important purposes for studying the climate of exoplanets, it is not the only one. A lot of different and overlapping topics can be explored with numerical models, for example: understanding and explaining new observations constraining atmospheric structure, such as light curves, photometry, and spectra obtained with current telescopes or prepare the observations for non-transiting planets or planets that are not yet observable; extend the theory of atmospheric circulation to the wide range of planetary parameters encompassed by exoplanets; evaluate an Earth-like atmosphere response and evolution to different stellar inputs or orbital configurations; investigate the sensitivity to parameters which affect the equilibrium states and their stability.
Whatever the purpose, all our current (and probably future) knowledge about the conditions at the surface of several exoplanets derives from numerical simulations, by Radiative Transfer Models, Energy Balance Models or General Circulation Models. In these last years, several 3D GCM, have been built or adapted with the aim to simulate exo-atmospheres. They helped us to explore several scenarios for Earth-like exoplanets climate and they have proved to be very useful tools.
Related Researchers
G. Piccioni
Related Projects
WorkPackage C1: Climate of Solar System Planets