The lack of comprehensive high-quality data makes it difficult for weather models to
provide accurate predictions for rainfall. This can result in great damage or even loss of life if severe
weather warnings are delivered late or not at all. This is particularly true for upland areas. So in order
to get a handle on the problem, the Delft University of Technology has decided to participate in a major
international experiment in the Black Forest, Germany, which will help scientists to better understand
the causes of rain. Running from 1 June to 1 September 2007, the experiment is using an airship and
other aircraft, as well as ground-based observations.
The Black Forest experiences many thunderstorms over the summer months.
Rain is created via a range of physical processes, which can interact with one other on a scale ranging from a few micrometres to 100 kilometres. Weather models use a scale of a few kilometres, while physical processes occurring on a smaller scale have to be approximated. An example of this is the formation of clouds. The sheer complexity and differences in scale result in inaccuracies when attempting to predict the time, place and amount of rainfall.
The Black Forest was selected as the site for experiments because it experiences many thunderstorms during the summer months, and discrepancies between predicted and actual rainfall are huge. Five temporary observatories with state-of-the-art remote sensing equipment are spread out over a 10 000 km2 area. In July, nine aircraft and an airship will be used to undertake detailed measurements above, below and in the clouds. Large-scale data will be collected by satellite.
Delft’s transportable atmospheric radar (TARA) was placed on the summit of the Hornisgrinde, one of the tallest peaks in the Black Forest, at the start of June. TARA is being used to measure the atmosphere, along with other instruments like light detection and ranging instruments (LIDAR), radiometers and cloud radars. The University also plans to make use of two research aircraft (one French and one German) that will fly through the clouds in order to measure their physical properties.
The work of Delft University of Technology is concerned with how cloud and rain formation is influenced by dust particles contained in the atmosphere. It forms part of the international Convective and Orographically-Induced Precipitation Study (COPS). The main objective of COPS is to identify the physical and chemical processes responsible for the deficiencies in forecasting rainfall over low-mountain regions.
One of the least understood aspects of climate models is the aerosol-cloud interaction on the earth’s radiation balance. The information collected during the COPS experiment over Germany’s Black Forest this summer will be ideal for updating and improving computer models that describe the interaction between atmospheric dynamics and cloud formation.
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