OBJECTIVES OF THE BBC2-CAMPAIGN
OBJECTIVES OF THE BBC2-CAMPAIGN |
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Clouds show a high variability in both time and space, have complex interactions with radiation and do have (strong) inhomogeneous structures. These characteristics make clouds hard to monitor and to model. Our present (limited) knowledge of cloud processes and their representations in climate and weather forecasts models limits out ability to predict clouds. The BALTEX BRIDGE Campaign (BBC) was performed in response to the need for a better understanding of these cloud processes.
The objectives of the BBC2-campaign are more or less similar to those of the previous BBC-campaign. During the Science Meeting on 14th of November, 2002, participants expressed their specific interest in the framework of the BBC2-campaign. A preliminary list of objectives expressed before the meeting by several of the participating research groups is presented here in no particular order.
Victor Venema (1), Clemens Simmer (1), Markus Quante (2)
(1) Meteorological institute University Bonn, Bonn, Germany
(2) GKSS Research centre, Geesthacht, Germany
Improvement of the radiative transfer calculations in NWP and climate models through inhomogeneous clouds. To achieve this 4D-clouds goal we need measurements of the cloud structure, cloud cover, LWP power spectrum, cloud boundaries, cloud layers, etc. These measurements will be used to generate 3D-cloud fields with a search algorithm for the radiative transfer calculations.
Jean-François Millot, Yvonick Hurtaud, Jean-François Kerdraon
Centre d’électronique de l’armement
The main goal of this project is to get infrared images of clouds (base and top) for:
Those image must be collected with contextual information needed by the 3D radiative transfer model : base and top altitude of cloud, cover ratio, LWC, LWP, albedo of cloud base and cloud top, optical thickness, temperature and humidity). This approach is based on the combination of in-situ aircraft, remote sensing aircraft and ground-based measurements. The geometry of observation depends on the availability and the relative position of aircrafts. It is very important to notice that the line of sight of ground-based infrared imager is not vertical but 10° above the horizon (it is important to notice that cloud structure - optical thickness, base altitude, etc -could not be measured with the instruments based in Cabauw) and that the line of sight of those in aircraft is 10° under the horizon.
Victor Venema (1), Clemens Simmer (1), Markus Quante (2)
(1) Meteorological institute University Bonn, Bonn, Germany
(2) GKSS Research centre, Geesthacht, Germany
This project has two goals, firstly, to quantify the error made in validation studies of cloud retrievals of LWC profiles with ground based remote sensing due to the 3D-structure of clouds. Based on this quantification method, one can, secondly, investigate which validation method performs best. Therefore, we need measurements of cloud structure (we can easily combine data from various instruments with our evolutionary search algorithm thus the more the better) and simultaneously in-situ measurements of LWC profiles.
Victor Venema
Meteorological institute University Bonn, Bonn, Germany
Investigate if the radar reflections in stratocumulus and cumulus are dominated by scattering due to Poisson distributed cloud droplets, spatial humidity structures (usually called Bragg scattering), or due to spatially correlated droplets (coherent particle scattering).
Dagmar Nagel
GKSS Research Centre, Institute for Coastal Research, Geesthacht, Germany
The validation of ground-based and remote sensing data (ENVISAT) for the development of correction algorithms due to the influence of clouds, their optical and microphysical properties on satellite data. The second aim of the project is the measurement of microphysical aerosol properties in the PBL and the investigation of aerosol-cloud interaction. For that, profiles and horizontal legs below, inside and above the clods should be flown with as many overpasses over the remote sensing side as possible. A co-ordination with satellite overpasses is desirable but not urgent.
Manfred Wendisch, Evelyn Jäkel, Sebastian Schmidt, Holger Siebert
Institute for Tropospheric Research, Leipzig, Germany
As a result of our discussion at the Leipzig BBC workshop and in Toulouse we propose a somewhat different approach for tackling the cloud enhanced absorption problem during BBC-2. It is based on the combination of balloon, aircraft and ground-based measurements. The balloon shell be used to characterize the microphysical properties of the cloud field, whereas the aircraft is concentrating on the radiation measurements above the cloud. Below- and in-cloud measurements with the aircraft are not attempted, instead at the surface a spectrometer, similar to that installed on the aircraft will be deployed. Additionally pyranometer measurements at the surface will be included. The balloon will perform continuous vertical profiling of the cloud layer and thus the microphysical measurements with the balloon will characterize the temporal and spatial cloud inhomogeneity in detail. The advantage of using two instrumental platforms (balloon and aircraft) for the airborne measurements is that the aircraft may sample and average a larger area above the cloud, which yields measurements that are more representative. With this approach, the airborne and ground-based radiation measurements are performed simultaneously with the balloon microphysical sampling.
Fred Bosveld (1), Henk Klein Baltink (1), Cindy Werner (2), Jordi Vila (3), Eddy Moors (3), Alex Vermeulen (4)
(1) Royal Netherlands Meteorological Institute, the Netherlands
(2) Geological and Nuclear Sciences, New Zealand
(3) WUR, The Netherlands
(4) ECN, The Netherlands
Observe the profiles of fluxes in the convective boundary layer for wind, temperature, humidity and carbon dioxide to understand their atmospheric budgets. Assess the added value of turbulence characteristics derived from ground based remote sensing sensors, i.e. windprofiler for clear sky part and cloud radar for boundary layer clouds.
Remko Uijlenhoet
Hydrometeorology, Wageningen University, the Netherlands
Obtaining a better understanding of the origins and parameterization of the micro- (i.e. discrete) and the macro- (i.e. continuous) structure of rainfall. This is important for 1) an improved parameterization of rainfall in climate and weather prediction models; 2) an improved quantitative use of ground-based and space-borne (e.g. Global Precipitation Mission - GPM) weather radars. Moreover, the space-time variability of rainfall over a range of scales has many important applications in hydrometeorology and other environmental sciences.
Han van Dop, Keitth M. Wilson
IMAU, Utrecht University, The Netherlands
The aim is to provide radiation and in-situ observations for cumulus and broken stratocumulus clouds to complement the remote sensing and ground based in-situ measurements. Also to provide a link between the ground based and the satellite observations. From long horizontal legs below and above the cloud the transmission and albedo of solar radiation will be determined. Horizontal in-cloud legs will determine the micro- and macrophysical properties of the cloud, in order to study their effect on the solar radiation field.
Michael H. Smith
Institute for Atmospheric Science, University of Leeds, Leeds, UK
Improvements in our understanding of the influence of aerosol particles on the microphysical characteristics of stratiform clouds. This will be accomplished by deploying a group of small, lightweight particle counters developed at Leeds (minimum 3) just below, at and just above cloud base. Given suitable meteorological conditions (light winds and moderate updraughts), this experiment should give a true Lagrangian study of the activation of aerosol particles to produce cloud droplets.
Arnout Feijt, Dominique Jolivet, Rob Roebeling
Royal Netherlands Meteorological Institute, de Bilt, the Netherlands
Our goal is to validate cloud products from MSG and AVHRR, which are produced with the retrieval algorithm that KNMI developed for EUMETSATs SAF on Climate Monitoring : cloud phase, optical thickness, LWP and cloud particle size.
Wouter Knap, Piet Stammes
Royal Netherlands Meteorological Institute, De Bilt, the Netherlands
Performing a clear-sky shortwave radiation closure study: radiative transfer calculations versus measurements of direct and diffuse irradiance. To perform the closure study we need accurate irradiance measurements and measurements of atmospheric state variables, like aerosol optical thickness, water vapour, ozone, etc. Furthermore we need measurements of the spectral surface albedo. The atmospheric and surface albedo measurements will be used as input for the radiative transfer model.
Piet Stammes, Juan Acarreta, Martin de Graaf
Royal Netherlands Meteorological Institute, De Bilt, the Netherlands
Our goal is to validate cloud and aerosol data products from SCIAMACHY produced with
the operational data processor (ESA) and our own retrieval algorithms:
- cloud phase (own algorithm)
- cloud top pressure (own algorithm)
- UV aerosol index (operational and own algorithm)
- aerosol optical thickness (own algorithm in development).
A. Pier Siebesma (1), Stephan de Roode (2)
(1) Royal Netherlands Meteorological Institute, the Netherlands
(2) IMAU, Utrecht University, the Netherlands
Mixing of cumulus clouds and their environment is a key mechanism that needs to be parameterized in any convection scheme. However, very few measurements of this mixing mechanism are available. In order to determine these entrainment rates it is necessary to have accurate and high-frequency measurements of temperature, humidity and liquid water inside and outside cumulus clouds. This can be obtained by the flight tracks of the Merlin in the cloud layer but also by the Leipzig tethered balloon. Since various entrainment parameterizations are formulated in terms of incloud vertical velocity, it would be desirable to have additional vertical velocity measurements
A. Pier Siebesma
Royal Netherlands Meteorological Institute, the Netherlands
The concept of a statistical cloud scheme is that cloud cover and cloud liquid water can be easily derived if the variability of humidity and temperature is given. These schemes have been developed and evaluated with cloud resolving models but hardly with insitu observations. By analyzing long straight flight tracks with high frequency measurements of temperature, pressure and humidity and liquid water these schemes can be evaluated
A. Pier Siebesma
Royal Netherlands Meteorological Institute, the Netherlands
Determination of the cloud base properties as a function of subcloud layer properties. In convection parameterization the cloud base properties (i.e. cloud base temp, humidity and vertical velocity are are usually parameterized in terms of surface fluxes and subcloud layer profiles of temperature and humidity. By simultaneous measurements of cloud base variables, surface fluxes and subcloud layer profiles it is possible to evaluate the various subcloud layer parameterizations. Surface flux measurements are provided by the Cabauw site, Subcloud layer profiles can be obtained by radiosondes and the Leipzig tethered balloon. The cloud base properties can be obtained lidar and cloud radar and by insitu measurements of the Leipzig tethered balloon.
A. Pier Siebesma
Royal Netherlands Meteorological Institute, the Netherlands
The key mechanism that controls the (Scu) boundary layer equilibrium and the breaking up of Scu is the top-entrainment flux of heat and moisture. The use of a tethered balloon offers a unparalleled opportunity to make direct measurements of these fluxes and test top-entrainment instability criteria.
Gerrit de Leeuw
TNO-FEL, the Hague, the Netherlands
Aerosol particle size distributions and the concentrations of their volatile components will be measured during BBC2 to provide information on the effect of aerosols on cloud formation and their microphysical properties. A scanning lidar will be used to obtain information on the vertical profile of aerosol backscatter in clear air and near cloud edges. A sun photometer will be used to provide information on the aerosol optical depth (AOD) at several wavelengths.
Iwan Holleman, Sylvia Barlag
Royal Netherlands Meteorological Institute, the Netherlands
Our goal is to assess the quality and availability of water vapour profile observations and boundary layer height estimations by remote sensing techniques. For this, we want to use profiles from Lidars systems and ceilometers. Radiosonde profiles and GPS data will be used for validation of water vapour profiles, and other remote sensing data will be used for validation of the boundary layer height.
Dave Donovan
Royal Netherlands Meteorological Institute, the Netherlands
To compare in-situ derived ice cloud particle size distribution parameters with those obtained using a combined lidar/radar technique.
D. Donovan (1), S. Crewell (2)
(1) Royal Netherlands Meteorological Institute, the Netherlands
(2) Meteorological institute University Bonn, Bonn, Germany
The goal of this activity is to quantify the extent of and frequency of occurrence of oriented ice crystals during BBC2. For a certain range of sizes and atmospheric conditions ice crystals may exist in preferred orientations. Direct backscatter from a vertically pointing lidar may be greatly enhanced compared to randomly oriented crystals. The degree of enhancement will depend on the type of crystals and the degree of `flutter' possessed by the falling crystals. Areas of aligned crystals may be distinguished from super-cooled water l ayers if the enhanced backscatter vanishes for a non-vertically pointing lidar. Thus multiple lidars (ceilometers) with different pointing angles will be deployed.