The Climates of Moist Terrestrial Planets

Earth was once considered unique as the only planet in the cosmos, an assertion we now know to be untrue. Many confirmed population of planets are terrestrial, whilst a not insignificant proportion of these possess atmospheres or even a condensable component such as water. We now know that the climates of moist terrestrial planets vary greatly; the work in this thesis sets out to improve our understanding of some of the processes that influence their climatic state. The three results chapters presented herein provide novel findings for different aspects of moist terrestrial climates, making use of a range of computational methods and model complexities. We find in Chapter 3 that for cloudy aquaplanets, the seasonal cycle and planetary albedo are heavily influenced by the planetary rotation rate and its subsequent impact upon large-scale dynamics. The presence of clouds was also found to delay the seasonal transition and modify the migration of the ITCZ in slowly rotating planets through feedbacks upon radiative balance. Chapters 4 and 5 present a number of results relating to tidally-locked planets; those that rotate such that one side permanently faces their parent star, much like the Moon does towards Earth. In Chapter 4 we show how a tidally-locked planet can develop cold-trapped moisture distribution. More specifically, we show that in planets with a higher initial surface moisture budget, an intermediate evolutionary state exists where a deep substellar lake develops that can exist for many millenia. The longevity of the lake is owed to a strong convective system at the substellar point coupled with a low lifting condensation level that limits the amount of water being cold-trapped on the night side. In Chapter 5 we show how the tendency for climates to enter a runaway greenhouse state is influenced by factors including insolation, moisture inventory and whether the planet is tidally-locked or not. Significantly we find that for a specified insolation and moisture budget, a tidally-locked planet is more likely to transition to a runaway state. For the same configuration, a tidally-locked climate also holds far more precipitable liquid in its atmosphere due to the non-linear dependence of the Clausius-Clapeyron relation and the hotspot at the substellar point.<p></p>