Introduction
The Cesar Observatory is located in the western part of the Netherlands (51.971° N, 4.927° E) in a polder 0.7 m below average sea level. At the site a large set of instruments is operated to study the atmosphere and its interaction with the land surface. The Cesar site is used for:
- Monitoring of long term tendencies in atmospheric changes,
- Studies of atmospheric and land surface processes for climate modelling
- Validation of space-borne observations
- The development and implementation of new measurement techniques
- Training of young scientists at post-doc, PhD and master level.
Three universities and five major research institutes collaborate in Cesar. It is the focal point of experimental atmospheric research in The Netherlands.
The aim is the development of the CESAR observatory to an EU-recognized measurement facility for long-term observation of essential climate variables. User-friendly data sets of coherent climate parameters in the atmospheric column will be derived by combining in situ and remote sensing observations to be used in process studies and to provide a generally applicable testing environment for climate and weather model evaluation and validation.
Site Description
A 213 m high mast was specifically built at the Cabauw site for meteorological research to establish relations between the state of the atmospheric boundary layer (ABL), land surface conditions and the general weather situation for all seasons. This site was chosen, because it is rather representative for this part of the Netherlands and because only minor landscape developments were planned in this region. Indeed the present surroundings of Cabauw do not differ significantly from those in 1972. The North Sea is more than 50 km away to the WNW. The nearby region is agricultural, and surface elevation changes are at most a few metres over 20 km. Within 40 km radius there are four major synoptic weather stations, among which is the regular radiosonde station at De Bilt (06260), ensuring a permanent supporting mesoscale network. Near the mast, the terrain is open pasture for at least 400 m in all directions, and in the WSW direction for at least 2 km. Farther away, the landscape is generally very open in the West sector, while the distant East sector is more rough (windbreaks, orchards, low houses). The distant North and South sectors are mixed landscapes, much pasture and some windbreaks. Therefore the highest mast levels have in all directions a long fetch of landscape roughness which is usefully similar to the roughness observed in the lower surface layer. The soil consists of 0.6 m of river-clay, overlying a thick layer of peat. The water table is about 1 m below the surface, but can be higher during wet periods.
The Cabauw tower
On the mast itself no undisturbed measurements can be made below 20 m. Auxiliary 20 m masts are installed to the SE and the NW at sufficient distance from the mast foot building. On site are also well-kept observation fields for micrometeorological observations, including soil heat flux, soil temperatures and various radiation measurements (including a BSRN station). Remote sensing observations are mostly performed at the Remote Sensing Site located 300 m SSE of the main tower. A scanning X-band radar operated by Technical University of Delft is located on top of the tower. In preparation of the EUCAARI campaign in 2009 an air inlet was installed at 60 m level. Air from this level is pumped through a pipe to the basement where several analysers are installed.
Data Access
Close-up of Cabauw tower with instrument booms and air inlet pipe
Timely delivery and accessibility of the data collected is of great importance for all users of Cesar data. The option of early comparison of data acquired during the Cesar continuous operational program or intensive field campaigns leads to improved understanding of instrument performance and improvements in the observational data stream. Also scientists not directly involved in the acquisition of the observational data benefit by timely access to the acquired data to accelerate their own research programs and can, on the other hand, contribute to the field program by a feedback on data quality or improved observational strategies. Early sharing of available data helps to ensure that the full benefit from the Cesar observations is realized. This can only be successful if the data are accessible, well documented and archived. Therefore the Cesar consortium initiated a project to develop, operate and maintain a central webportal for access to the Cesar Observatory products.
The webportal and database were developed by the Royal Netherlands Meteorological Institute (KNMI) in cooperation with and feedback from the Cesar partners. The KNMI also hosts and maintains the webportal and database.
Click here for the CESAR Database System webportal.
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