Investigation of cloud by ground-based and airborne Radar and Lidar (CARL)








The CARL project is a joint effort involving research teams from Germany, France, Greece and the Netherlands. It is a three years project, started in December 1997, in the European Commision's RTD programme " Enviroment and Climate". New methodologies will be tested in order to derive microphysical parameters of warm and cold clouds during several campaigns involving groud-based and airborne radar and lidar systems. The most interesting cases of the experimental campaigns will be simulated with an advanced limited area model. A significant effort has been devoted in the intercomparison between the collected data from the observational systems and the model outputs. The model used for the simulations is the Regional Atmospheric Modeling System, RAMS.






GKSS Research Center Geesthacht, Institute of Atmospheric Physics, Max Planck Strasse D-21502 Geestacht, Germany



M.Quante (, tel: 494152871501, fax:494152872020

O.Danne (, tel: 494152871520, fax:494152872020

F.Albers (, D.Milferstadt, fax:494152872020



Institut Pierre Simon Laplace, 10-12 avenue de l'Europe, 78140 Velizy, France



J.Testud (, tel:33139254476, fax: 33139254922

F.Baudin (, tel:33139254850, fax: 33139254872

P.H.Flamant (, Ecole Polytechnique, 91128, Palaiseau, France, tel: 33169334550, fax:33169333005

J.Pelon(, Universite Pierre et Marie Curie,T14,E5,B102,4,Place Jussieu,75252, Paris cedex 05, France; tel: 33144273779, fax: 33144273776


National and Kapodistrian University of Athens (NKUA), Department of Physics, Division of Applied Physics, Atmospheric Modeling and Weather Forecasting Group, Panepistimioupolis, Bldg PHYS-V, 15784, Athens, Greece.



G. Kallos (, tel: 30 1 7276923, fax: 30 1 72 95 281

E. Mavromatidis (, tel: 30 1 7276832, fax: 30 1 72 95 281



KNMI, Koninklijk Nederlands Meteorologisch Institut, Postbus 201, 3730 AE De Bilt, Wilhelminalaan 10.




Hannelore Bloemink (






The main objectives of the project are:


  • To validate and improve cloud parameterizations in atmospheric models, detailed information about the cloud characteristics must be available on large scales. Crucial cloud characteristics to the cloud radiation budget, e.g. the particle size distribution (liquid or ice, as represented by the effective radius re ) and liquid or ice water content ( phase and W ), are presently poorly measured at such a scale. New measurements from airborne and spaceborne platforms will be utilized in order to allow cloud sampling on large horizontal scales. The objective of this work is to prepare such developments by testing new observational remote sensing methods combining lidar and radar systems.

  • To test different procedures involving several wavelengths, polarization, lidar fields of view and multi-beam analysis and ground-based versus airborne observations for the retrieval of the cloud parameters. As a first step, procedures will be tested, by using ground-based measurements and in-situ cloud sampling for warm clouds. In a second step airborne lidar and radar system will be involved.

  • Model simulations will be performed in order to analyze the impact of the cloud parameterization, on the radiation and dynamics at the mesoscale. The simulated fields and microphysical processes will be used also to provide a feedback on the measuring systems and especially the prototype ones (e.g. new radars at 96 GHZ, LIDAR).





    During the project, a cloud Radar (with polarization diversity to discriminate water and ice phases and Doppler capabilities) and two backscattering Lidar ( with polarization diversity) will be operated from the same site and airborne platform. The target of the measurements is high, middle and low level clouds. The main objective is to retrieve the effective radius and the water content of such clouds. To do so, it is aimed at deriving the second and third moment of the cloud droplet distribution from lidar and radar signal analysis, and to correct for diffraction and multiple scattering. Model calculations will be performed to analyze the impact of the retrieval and related errors, and check the quality of retrieved cloud parameters and their representativeness, with reference to radiation budget parameters measured at the same time. The atmospheric model will be used to perform multi-scale simulations with a state of the art cloud microphysical parameterization module activated. Two-way interactive nesting capabilities of the model will be used in order to cover a regional scale area and simultaneously to obtain very high resolution over the experimental location.




    Two experimental campaigns have been organized so far and a third is under way. The main task of the Atmospheric Modeling and Weather Forecasting Group of the University of Athens (NKUA/AM&WFG) is to perform the appropriate model development and simulations with RAMS and inter-compare the results with the observations from the experimental radar and lidar platforms.


    1st experimental campaign


    Location: Geestacht

    Date: 6 December 1995

    Period of observations: 8 minutes, from 16:06 UTC to 16:14 UTC.

    Instruments: The GKSS 95 GHz cloud Radar.


    (click here)


    2nd experimental campaign


    Location: Palaiseau ( near Paris)

    Period of observations: 26 April to 15 May 1999



    For ground-based measurements: 5.5 GHz Radar (IPSL), 95 GHz Radar (GKSS), Lidar 0.53 and 10.6 mm (IPSL), Lidar ceilometer 0.9 mm (KNMI), visible and infrared radiometers ( KNMI, IPSL)


    For airborne measurements: FSSP, 2DC, 2DP sondes(GKSS), Visible and infrared broadband radiometer, narrow band narrow beam infrared radiometer( Meteo-France)


    Flights : Five flights were performed during the campaign with the Merlin aircraft ( Meteo-France, subcontractor of IPSL) to get the observed cloud microphysics, for comparison and validation.



    (click here)



    Additional model simulations for the 2nd experimental period


    In order to investigate the model sensitivity to various settings, a number of additional simulations were performed. The new version of RAMS (4.2.9) was used. A number of figures have been prepared, especially in the form of time-versus-height form for better inter-comparison with the experimental observations (Radar, Lidar, ceilometer) and conventional measurements (soundings)


    (click here)



    A quick description of RAMS


    RAMS is a highly versatile numerical code developed by scientists at Colorado State University and Aster Division of Mission Research Inc. ( for simulating and forecasting meteorological phenomena (Walko and Tremback, 1996; Pielke et al., 1992). It is considered as one of the most advanced modeling systems available today. It is a merger of a non-hydrostatic cloud model (Tripoli and Cotton, 1982) and a hydrostatic mesoscale model (Mahrer and Pielke, 1977). It has been developed in order to simulate atmospheric phenomena with resolution ranging from tens of kilometers to a few meters. There is no lower limit to the domain size or to the mesh cell size of the model finite difference grid. A general description of the model and its capabilities is given in Pielke et al (1992). However some RAMS features are summarized in the following:


    1.      Two-way interactive nesting with any number of either telescoping or parallel fine nest grids (Clark and Farley, 1984).

    2.      Terrain following coordinate surfaces with Cartesian or polar stereographic horizontal coordinates.

    3.      Non-hydrostatic or hydrostatic time-split time differencing.

    4.      Cloud microphysics parameterization at various levels of complexity.

    5.      Various turbulence parameterization schemes.

    6.      Radiative transfer parameterizations (short and longwave) through clear and cloudy atmospheres.

    7.      Various options for upper and lateral boundary conditions and for finite operators.

    8.      Various levels of complexity for surface-layer parameterization (soil model, vegetation etc.).

    9.      Horizontally homogeneous or variable initialization (isentropic analysis). ECMWF and National Center for Environmental Predictions (NCEP) analysis files can also be used for initialization.

    10.  It is highly portable and runs on several types of computers.

    11.  A parallel version of RAMS is currently available for efficient use in high performance computers.