Fifty years of Atmospheric Boundary-Layer Research at Cabauw serving Weather, Air Quality and Climate.

An overview is given of 50-year Cabauw observations and research on the structure and dynamics of the atmospheric boundary layers (ABL). It is shown that over time this research site with its 200 m meteorological tower has grown into an atmospheric observatory with a comprehensive observational program encompassing almost all aspects of the atmospheric column including its boundary conditions. This is accomplished by the Cabauw Experimental Site for Atmospheric Research (CESAR) a consortium of knowledge institutes and of universities. CESAR plays an important role in the educational programs of the CESAR universities. The current ABL observational program is described in detail and the other parts of the CESAR program are described briefly. Due to an open data policy the CESAR datasets are used by researchers all over the world. Examples of results are given to the use of the long time series, model evaluation, satellite validation, and process studies. The role of tall towers is discussed in relation to the development of more and better ground based remote sensing techniques. CESAR is now incorporated into the Ruisdael observatory, the large scale atmospheric research infrastructure in the Netherlands. With Ruisdael the embedding of the Dutch atmospheric community in national policy landscape, and in the European Atmospheric Research Infrastructures is assured for the coming decade.