Atmospheres, dynamics Meteorology Earth

a b s t r a c t The question of climate at high obliquity is raised in the context of both exoplanet studies (e.g. habitabil-ity) and paleoclimates studies (evidence for low-latitude glaciation during the Neoproterozoic and the ‘‘Snowball Earth’ ’ hypothesis). States of high obliquity, /, are distinctive in that, for /P 54!, the poles receive more solar radiation in the annual mean than the equator, opposite to the present day situation. In addition, the seasonal cycle of insolation is extreme, with the poles alternatively ‘‘facing’ ’ the Sun and sheltering in the dark for months. The novelty of our approach is to consider the role of a dynamical ocean in controlling the surface climate at high obliquity, which in turn requires understanding of the surface winds patterns when temperature gradients are reversed. To address these questions, a coupled ocean–atmosphere–sea ice GCM configured on an Aquaplanet is employed. Except for the absence of topography and modified obliquity, the set-up is Earth-like. Two large obliquities /, 54! and 90!, are compared to today’s Earth value, / = 23.5!. Three key results emerge at high obliquity: (1) despite reversed temperature gradients, mid-latitudes surface winds are westerly and trade winds exist at the equator (as for / = 23.5!) although the westerlie