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++++++ CURRENTLY HIRING++++++
WG Complexity & Climate is currently hiring several ERC-funded PhD students and a postdoc. We offer attractive international collaborations.
See also research project INTERACTION.
For further information, please contact Prof. Dr. Jan O. Haerter.
Complexity & Climate studies the self-organization of convective cloud, e.g., thunderstorms, using high-resolution simulations, conceptual modeling and observations. Convective cloud dominates much of the rainfall and storminess in the tropics, and especially when thunderstorms organize into larger cluster, termed mesoscale convective systems, or MCSs (> 100 km in diameter), these groups of clouds can produce heavy rainfall. Over continents, such as tropical Africa, MCS are very common and show typical diurnal, i.e. day-to-night, variations.
Over the ocean, diurnal variation is weaker and cloud organization is more "long-term," with clusters organizing over several days. Dependent on sea surface temperatures and the details of interaction with the surface, clusters can grow into tropical cyclones (TCs). TCs are extreme events, that heavily impact tropical or sub-tropical coasts.
A particular focus of the group is on the special role played by the coasts, technically: the interface between regimes mentioned, in experiencing and promoting the organization of cloud clusters.
Through the PI's double affiliation, there is strong collaboration and scientific exchange with the Atmospheric Complexity group at the Niels Bohr Institute, University of Copenhagen.
Crowding of thunderstorms leads to runaway heavy rainfall
Thunderstorms are fascinating, as they produce spatially rather confined rainfall, which can be quite heavy and cause substantial flooding. Flooding is much more pronounced when single thunderstorm "pillars" join together in space so that a wider area is covered by heavy rainfall events - leading to extremes. Such clusters of thunderstorm events are, therefore, of high scientific interest, yet, it is not well-understood how they form.
Our study shows that under relatively simple conditions, such thunderstorm events emerge spontaneously, that is, without an external driver causing them to develop. All it takes is that the surface temperature repeatedly varies by several degrees Celsius between night and day (see Animation). In this case, clusters of thunderstorms, 180 km across and with a duration of 6 hours, spontaneously develop, leading to heavy rainfall. In contrast, when the temperature varies less between day and night, no such clustering is found - rainfall is modest throughout the simulation domain.