Drizzle Radar: A Gain For Climate Research

The radar was successfully installed on the 213 metre-high Royal Netherlands Meteorological Institute (KNMI) measurement tower in Cabauw, near Lopik, on Thursday, August 23. From this spot the highly sensitive radar, together with the other advanced instruments of the CESAR observatory (Cabauw Experimental Site for Atmospheric Research), is to provide a complete picture of the interaction between dust, clouds, rain and radiation. The latter is still one of the least understood factors in climate models.

Clouds and the climate

Clouds are of great importance for the greenhouse effect. On the one hand, clouds wrap a blanket round the Earth which retains heat, but they also cool the planet through the reflection of sunlight. Clouds can therefore compensate for some of the global warming, but the question is how much, and how precisely does it work. Dust particles play a crucial role in the formation of clouds and precipitation. They act as condensation nuclei, around which small droplets form. In an atmosphere without dust, clouds would not even be able to form. The more dust particles, the more clouds, the more solar radiation is reflected and the cooler the Earth stays.

A cooler Earth leads, in its turn, to less precipitation, because cooler air cannot hold as much moisture as warm air. Thus we have an extremely complicated interplay of factors that can be elucidated only through detailed measurements. The new 'Drizzle radar' is able to measure cloud droplets and precipitation extremely accurately. In addition, the measurement tower in Cabauw monitors the quantity and composition of dust particles and of clouds. Climate researchers are particularly interested in the extent to which dust particles influence rainfall.

IDRA

The International Research Centre for Telecommunications and Radar (IRCTR) Drizzle Radar, or IDRA, developed by TU Delft, is able to measure the smallest raindrops in a thirty kilometre zone around the observatory. The data are used to determine cloud life cycles, and their relationship to radiation and airborne dust These measurements, which will lead to a better understanding of the climate system, are unique in the world and can be done nowhere else.

CESAR

The CESAR Observatory in Cabauw is one of the world’s most advanced observatories for atmospheric research.  Its highly accurate, multi-instrument array constantly measures atmospheric characteristics , to obtain a better picture of the atmosphere’s role in the climate system. The most eye-catching feature is the 213 metre-high measurement tower of the KNMI, where the Drizzle Radar has now been installed. CESAR is a consortium of KNMI (Royal Netherlands Meteorological Institute), TU Delft (Delft University of Technology), TNO (Netherlands Organisation for Applied Scientific Research), RIVM (National Institute of Public Health and Environmental Protection), ECN (Energy Research Centre of the Netherlands), Wageningen University and ESA (European Space Agency).