Recherches environnementales

Direct Numerical Simulation of geophysical flows

Prof. Dr. Youri Podladtchikov

The driving motivation of this project is to bring a computational approach as a prediction tool for environment hazards such as landslides, or rock - and snow avalanches. Modeling such events requires to deal with large uncertainties on the initial conditions, and with turbulent flows of heterogeneous materials which experiences a chaotic evolution. This implies major issues in terms of accuracy, stability and scalability of the numerical algorithms, but may also require the develpment of specific rheological models since theses materials exhibit viscous,elastic and plastic behaviours. In this perspective, the simulation of a long run-out-avalanche is envisaged. Among such events, the Frank slide (Alberta, Canada) is one of the most documented in terms of initial and final conditions. The comparison of the numerical simulations with these measurements is a mandatory step in terms of validation. Moreover, it may provide new insights on the fundamental mechanisms of avalanche propagation which are not yet understood and thereby enable the improvement of the simplified models used to date.

Stability of the Atlantic meridional overturning circulation

Dr Maura Brunetti

Researcher at the Institute for Environmental Sciences. UNIGE

27 November 2013

The Northward head transport via the North Atlantic meridional overturning circulation has a critical role in high-latitude climate and in particular in the temperate climate of Northwest Europe.

Paleoclimate reconstructions have shown that the overturning cell can change its operation mode (from 'ON' to 'OFF' state) on decadal time scales, giving rise to significant climate impacts (e.g Heinrich events during the last ice age). The stability properties of the Atlantic Meridional overturning circulation have been investigated through climate numerical models of different complexity. They generally confirm the existence of switches between On and OFF modes, which depend on outbursts of fresh- water into the Atlantic ocean. However, the physical processes which effectively determine the state of the Atlantic Meridional overturning circulation are not yet fully understood. We investigate the freshwater budget of the Atlantic basin using an intermediate complexity code, the MIT general circulation model in the configuration where ocean and sea-ice dynamics are coupled to simplified descriptions of atmosphere and land. We compare different stability indicators proposed in the literature and discuss how the salinity content affects the behaviour of the North Atlantic ocean circulation. In particular, we investigate nonlinear dependences of the ON/OFF mode on the averaged salinity content in the Atlantic ocean.