| dc.description.abstract | Utilizing the Earth System Model IPSL-CM5A2 and the Atmosphere-Land Surface
Model LMDZOR6 v2.2, I conduct simulations of the South American Monsoon
System (SAMS) during the Mid-Miocene Climatic Optimum (MMCO), a warm period
∼15Ma before present. A 3000-year IPSL-CM5A2 simulation is performed
with Mid-Miocene boundary conditions, including a pCO2 of 840 ppm, finding a
MAT increase of 8.85K compared to the preindustrial. Simulated MMCO SSTs
are then used to force LMDZOR6 to benefit from a higher spatial resolution, more
developed parameterizations of convection, and new radiative and soil hydrology
schemes. For the positive SAMS phase in the MMCO, the simulations consistently
demonstrate an intensification of the hydrological cycle in the core regions and decreased
precipitation in the Central Andes and La Plata Basin, accompanied by a
strengthening of all SAMS components apart from the South American Low-Level
Jet. The main convective activity shifts from the SACZ to the eastern Amazon,
resulting in a more northern Bolivian High, while the main SACZ activity relocates
over the southern tropical Atlantic. Diverging signals are found for the MMCO’s
negative SAMS phase, with increasing precipitation in IPSL-CM5A2 and decreasing
precipitation in LMDZOR6. Dynamical vegetation experiments show an expansion
of tropical biomes up to 30◦S. Dynamical versus static hydrological vegetation feedbacks
are identified but found to be small compared to differences between model
generations. The study shows how MMCO-warmth and paleogeography affect different
parts of the monsoon circulation and might help to understand past, as well
as possible future changes in the SAMS. | |
