Overview of research and networking with ground based remote sensing for atmospheric profiling at the Cabauw experimental site for atmospheric research (Cesar) - the Netherlandse

CESAR, the Cabauw Experimental Site for Atmospheric Research, is the Dutch focal point for collaboration on climate monitoring and atmospheric research and is situated on the KNMI meteorological research site near Cabauw in the Netherlands (Cabauw, 51.97 N, 4.93 E). CESAR addresses challenging topics in atmospheric research, especially the questions that are related to the interaction between clouds, aerosols and radiation and questions dealing with land-atmosphere interaction. These topics are approached via process studies, model evaluations, climate monitoring, development of new experimental techniques and supporting activities for satellite missions. For each of these approaches, specific demands are put on the instrumentation, mode of operation and overall infrastructure. The station has large benefits to offer for atmospheric science, both in the Netherlands and internationally. It provides a platform for collaboration in this important field and will provide the routine observations needed to assess the impact of the different atmospheric parameters on local climate. The station fits in directly in the selected group of global monitoring networks that are currently operational or are being set-up to address the problems of climate change. One of CESARs strengths lies in the integrated approach of atmospheric profiling and on studying aerosol-cloud interactions using advanced multi-sensor techniques. These are used to fill one of the largest gaps for improving the understanding of our climate. CESAR integrates many essential measurements that are needed to increase understanding of climate, air quality issues and observations needed for assimilation in NWP models. These observations include profiles of wind, aerosols, clouds, water vapor and precipitation, as well as radiation. The resulting anchor-point provides much needed interrelationships between the fields of research. CESAR serves as a test bed for an in-depth understanding of existing measurement techniques, development of new measurement techniques that take advantage of availability of multiple sensors, intercomparisons for climate research, and air quality monitoring. Last but not least, use is made of the possibilities of the research station for validating and improving satellite measurements. The perspectives from space observations and ground based measurements are complementary: from space a global overview is obtained, built up from snap-shot like observations over different locations, while a temporal development over one place is obtained from a ground based station. Ground-based stations have the ability to provide spatio-temporal development of the state of the atmosphere for many parameters simultaneously, and in much greater detail than from space. This offers a unique opportunity for validation of observations from space. The complete picture can only be obtained through the combination of both perspectives. An overview will be given on developments in the instrumental suite at Cabauw that was recently augmented with a scanning drizzle radar (IDRA) and a multi-wavelength Raman lidar for aerosols, clouds and water vapor (Caeli). Also, an overview will be given of routine observations and campaigns (intensive observation periods) carried out in the past and planned for the future. Ongoing research projects at CESAR will be illustrated by examples. The final part of the paper will high-light participation in (global) observation networks (e.g. EARLINET, BSRN, Aeronet, EMEP, etc.) that will spill over to the prospects of a network of observatories on European scale.