| dc.description.abstract | Projected precipitation changes due to increasing greenhouse gas concentrations exhibit considerable spatial structure with increases in the mid- to high-latitudes, and decreases in the subtropics. In the Equatorial regions, precipitation is pro- jected to increase over oceans, over Africa and over the Maritime Continent, but to decrease in the Amazon basin. The decrease in precipitation over the Amazon basin and increase over the Maritime Continent are both enhanced in response to plant physiological changes. The aim of this thesis is to identify basic controls on tropical precipitation change over ocean and land, with a particular focus on the zonal asymmetry in the Equatorial region and amplification of precipitation changes due to vegetation. We find that soil-moisture limits on evaporation and a teleconnection between Equatorial Africa and the Amazon basin contribute to the zonal asymmetry in rainfall changes over the two regions. When vegetation changes are included, the amplification of the drying over the Amazon basin is largely due to relatively weak local evapotranspiration, providing further evidence that loss of the Ama- zon rain forest could lead to strong decreases in rainfall. Furthermore, we find that tropical precipitation changes over a warm surface temperature anomaly are related to changes in the atmospheric energy budget, and that monsoon-type rainfall behaviour can be obtained even when the thermal inertias of land and ocean are the same, thus partly contradicting the historical view of monsoons as a large-scale land-sea breeze. Our findings are based on idealised Atmospheric General Circulation Model simulations with continental configurations ranging from flat rectangles to realistic continents with topography. Despite their simplicity, the simulations exhibit pre- cipitation changes similar to complex General Circulation Models, indicating that the mechanisms identified here contribute to tropical rainfall changes on Earth. | en_GB |
