Our Research

The Tropics, i.e. the area between the tropics of Cancer and Capricorn, cover about 40% of the Earth’s surface. Throughout the year the earth-ocean-atmosphere system gains energy in this region, which drives important components of the general circulation such as the Hadley cells, the “El Niño-Southern Oscillation (ENSO)”, monsoons and not least tropical cyclones. Including the subtropical parts of northern India and East Asia that are influenced by the Asian monsoon, the majority of the world’s population lives in the tropical climate zone – with tendency to rise.

Food security and livelihoods in many tropical countries depend on rain-fed agriculture and therefore on abundant but not too extreme precipitation, the most important climate parameter socio-economically in the Tropics. The predictability of tropical rainfall on time scales from few hours to several days, in many regions also on seasonal and decadal timescales, however, is surprisingly small. A prime example is the region of the West African monsoon, one of the research foci of the WG “Atmospheric Dynamics”. During boreal summer, extensive and long-lived convective complexes form in this region, some of which turn into seedlings for Atlantic hurricanes after crossing the West African coast. Numerical simulations of these cloud complexes, which often span more than 100,000 km², require a solid understanding and sound representation of surface energy fluxes, of turbulent fluxes of energy and momentum in the planetary boundary layer and in the thunder clouds as well as of cloud microphysical processes, which are influenced by Saharan dust and anthropogenic aerosols.

These enormous tropical thunderstorms cause an efficient interaction between small-scale processes near the surface and the larger-scale circulation. These complex processes are not resolved or simulated realistically in global weather forecast models. In a hitherto unprecedented comprehensive study regarding the predictability of convective rainfall over northern tropical Africa, Vogel et al (2018) demonstrated that nine numerical global weather forecast models did not provide more skillful forecast than statistical methods based on past observations. in turn, large-scale tropical and extratropical wave phenomena impact on the initiation and growth of tropical thunderstorm complexes. Members of the WG “Atmospheric Dynamics” have shown this in recent publications for southeast Asia (van der Linden et al. 2016; van der Linden et al. 2017) and West Africa (Engel et al. 2017; Knippertz et al. 2017).

An innovative research approach that members of the WG pursue at the moment in collaboration with colleagues from Applied Mathematics is to test if the better predictability of large-scale wave phenomena can be utilized in statistical methods to improve (extreme) rainfall predictions on the ground. Progress would be of immediate benefit for smallholding farmers in tropical Africa and Southeast Asia.