Clouds and climate change

What role do clouds play in global warming? An international consortium, which includes LMU physicist Bernhard Mayer and his team, hopes to clarify this issue by carrying out a wide range of measurements and observations in the Caribbean.

Photo: Tobias Kölling/LMU

Photo: Tobias Kölling/LMU

Clouds are a major component of Earth’s climate. However, the impact of global warming on the nature and extent of cloud formation, how such changes affect circulation patterns and how the latter in turn influence the future course of climate change are questions that remain unanswered. Clouds have significant impact on the Earth’s energy budget, as they reflect part of the incoming solar radiation back to space, which has a cooling effect. But clouds also contribute to warming because they reduce the level of thermal radiation that can be emitted to space from Earth’s surface. Moreover, the relative impact of steadily rising temperatures on these two fundamental processes is unclear. Current climate models are only able to represent clouds in an approximated way which leads to further uncertainties in computer-based simulations of the future behaviour of the climate system.

An international consortium of scientists now hopes to shed new light on these issues. In a 6-week field study in the Caribbean, which begins on the 20th of January, the EUREC4A project will collect observational data that can be used to check, clarify and supplement current theories and climate simulations. The acronym describes the purpose of the campaign – Elucidating the Role of Cloud-Circulation Coupling in Climate – and the Caribbean was chosen as the ideal site for the campaign because it lies in the tropics. Here, the prevailing north-easterly trade winds are associated with the formation of shallow cumulus clouds – the most prominent type in the Earth’s climate system. These clouds normally reach altitudes of only a few kilometers, but their life cycles are complex. Below cloud basethe turbulent motions of moist, near-surface air give rise to small-scale circulation patterns, while the sinking of larger masses of denser, dry air affects the dynamics of their upper layers. The EUREC4A collaboration will make detailed observations relating to the interactions between these atmospheric and oceanic processes, which determine the balance between circulation, condensation and evaporation. The results will enable researchers to develop a better understanding of the formation and dissipation of these clouds.

The initial idea for the EUREC4A study was developed by teams based at the Max Planck Institute for Meteorology in Hamburg and the Laboratoire de Météorologie Dynamique in Paris. They succeeded in recruiting researchers from approximately 40 institutions for the project, including 13 located in Germany. The observation campaign will involve the use of four aircraft and four ocean-going research vessels, as well as ground-based remote sensing by the Barbados Cloud Observatory (BCO), which is run jointly by the MPI for Meteorology and the Caribbean Institute for Meteorology and Hydrology in Bridgetown. In addition, a new generation of satellite-based remote-sensing methods will be deployed, and the data obtained will serve as input for modern climate models that explicitly incorporate the effects of turbulence.

Among the participants in the project is Prof. Dr. Bernhard Mayer, who holds the Chair of Experimental Meteorology at LMU. He and his group have developed the specMACS instrument, which forms an important part of the instrumentation on board the HALO (High-Altitude and LOng-range) aircraft. specMACS is a high-end hyperspectral camera, which is designed to image clouds at high spatial and spectral resolution, revealing structural details that provide insights into their geometry, microphysics and temporal evolution. “My group and I can’t wait to get started,” says Mayer. “Since the last campaign three years ago, we have invested a great deal of work in our detectors and algorithms, and we are looking forward to carrying out and evaluating the observational data, which promise to provide entirely new insights into the microphysics of cloud formation.”

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