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  • Attenuated backscatter profiles from the CALIOP satellite lidar are used to estimate cloud base heights of lower-troposphere liquid clouds (cloud base height below approximately 3 km). Even when clouds are thick enough to attenuate the lidar beam (optical thickness > 5), the technique provides cloud base heights by treating the cloud base height of nearby thinner clouds as representative of the surrounding cloud field. Using ground-based ceilometer data, uncertainty estimates for the cloud base height product at retrieval resolution are derived as a function of various properties of the CALIOP lidar profiles. Evaluation of the predicted cloud base heights and their predicted uncertainty using a second, statistically independent, ceilometer dataset shows that cloud base heights and uncertainties are biased by less than 10%. CBASE provides two files for each CALIOP VFM input file: one using a 40 km window to detect the cloud field base height, and one using a 100 km window. (The input CALIOP VFM dataset is organized by the daytime/nighttime half of each orbit.) The file name pattern is CBASE<resolution>_<date>T<time><day/night>.nc (identical to the input CALIOP VFM file name with the exception of the product name). Files are organized into subdirectories by half-orbit start date.

  • The field experiment FRONTEX 1989 (FRONT EXperiment) took place in the German coastal area of the North Sea between 2 May and 6 June 1989. It was coordinated by the Meteorological Institute of the University of Hamburg and was primarily funded by the German Research Foundation (DFG) in the frame of the priority programme "Fronten und Orographie". The scientific aim was the investigation of cold fronts moving in from the North Sea and reaching the coastal area. The different physical properties of sea and land surface (roughness, humidity, temperature, heat conduction and heat capacity) modify the frontal structure at landfall. The modification should first alter the boundary layer and is then communicated to higher levels, thus effects like convection and convergence will be found farther inland. The experimental concept was to monitor the passing front on all relevant temporal and spatial scales. To obtain this goal a large variety of measurement platforms was employed. Ground based remote sensing and in-situ measurements were performed at Heligoland, Schleswig, Hanover, Emden, Berlin, and on board the research vessel. Three research aircraft (POLAR-2 and POLAR-4 of AWI Bremerhaven and DO-128 of TU Braunschweig) were used to measure the frontal structure with high temporal and spatial resolution.

  • The Convection and Turbulence Experiment (KonTur) was conducted in the southeastern part of the North Sea from 14 September to 21 October 1981 (with a break from 4 to 8 October). KONTUR aimed at two main scientific objectives. First, to observe the formation and time variation of regularly organized convection in the lower troposphere as a function of the mean atmospheric flow and the lower boundary condition and to quantify the dependence of the vertical transports of momentum, heat and water mass on various scales of motion in order to test existing convection models and to provide an observational background for the extension of theoretical concepts. Second goal was to determine the mean and turbulent quantities within the marine atmospheric boundary layer (ABL), including the large scale horizontal and vertical advection of momentum, heat and water vapour, cloud microphysics and the radiation field, in order to assemble a comprehensive data set for boundary layer modelling with first and second order closure methods. The experiment covered an area in the southeastern part of the North Sea (German Bight), roughly between latitudes 53¿N and 56¿N and longitudes 6¿E and 9¿E. Both the convection and the turbulence programme made use of the same experimental tools which can be subdivided in the following four groups: the central station occupied by the research vessel Meteor, the aerological network (Borkumriff, RV Meteor, RV Gauss/Poseidon, Research Platform Nordsee, Elbe 1), two aircraft (Hercules C-130, Falcon 20) and supporting observations, such as satellite images, cloud photography, surface and upper air large-scale fields from routine data. KONTUR 1981 was followed by the experiments KONTROL 1984 and KONTROL 1985.

  • KONTROL 1985 is part of research activities focused on organized convection phenomena as they are often manifested in organized cloud patterns like the well-known boundary layer cloud streets or open and closed cellular cloud structures. The experimental part of the investigations began with the experiment KonTur (Konvektion and Turbulenz) in September and October 1981. It continued with the experiments KONTROL in August 1984 and KONTROL in October 1985. All experiments took place over the German Bight in the southeastern part of the North Sea. The experimental concept based on the use of three fixed stations performing continuous aerological and surface observations and two aircraft conducting detailed observations during special periods. The stations were the island of Heligoland, the research vessel Valdivia and the research platform NORDSEE (54°42'N, 7°10'E). The aircraft were a FALCON-20 of DFVLR and a DO-28 Skyservant of the TU Braunschweig.

  • KONTROL 1984 is part of research activities focused on organized convection phenomena as they are often manifested in organized cloud patterns like the well-known boundary layer cloud streets or open and closed cellular cloud structures. The experimental part of the investigations began with the experiment KonTur (Konvektion and Turbulenz) in September and October 1981. It continued with the experiments KONTROL in August 1984 and KONTROL in October 1985. All experiments took place over the German Bight in the southeastern part of the North Sea. The experimental concept based on the use of two fixed stations performing continuous aerological and surface observations and two aircraft conducting detailed observations during special periods. The stations were the research vessel Valdivia and the research platform NORDSEE (54°42'N, 7°10'E). The aircraft were a FALCON-20 of DFVLR and a DO-28 Skyservant of the TU Braunschweig.

  • The field experiment ARKTIS 1991 was an expedition planned by meteorologists of the Collaborative Research Centre 318 entitled "Climatically relevant processes in the system ocean-atmosphere-ice" which is funded by the German Research Foundation and established at the University of Hamburg. The expedition took place in the Norwegian Sea between Northern Norway, Bear Island and Jan Mayen during the period 17 February until 15 March 1991. The main aim of the experiment was the investigation of cold air outbreaks from the surrounding Arctic ice sheets. During such weather episodes the air mass coming from the ice is rapidly modified over the water due to the contrasts in temperature, heat conduction, humidity and roughness between ice and water. This leads to the formation of a "new" boundary layer. Its depth, mean temperature and moisture increases with increasing distance from the ice edge mainly due to sensible and latent heat supply from the ocean. The investigations of cold air outbreaks and Arctic stratus by scientists of the Collaborative Research Centre 318 began already three years before with the field experiment ARKTIS 1988 which took place in the area west of Spitsbergen in May 1988. ARKTIS 1991 is a continuation of this work under winterly weather conditions. ARKTIS 1991 was followed by the experiment ARKTIS 1993. As in ARKTIS 1988 the research vessel Valdivia and the two research aircraft FALCON-20 of the DLR at Oberpfaffenhofen and DO-128 of the TU Braunschweig were at our disposal. Radiosonde measurements were performed on board of RV Valdivia and on Bear Island.

  • The field campaign LOFZY 2005 (LOFoten ZYklonen, engl.: Cyclones) was carried out in the frame of Collaborative Research Centre 512, which deals with low-pressure systems (cyclones) and the climate system of the North Atlantic. Cyclones are of special interest due to their influence on the interaction between atmosphere and ocean. Cyclone activity in the northern part of the Atlantic Ocean is notably high and is of particular importance for the entire Atlantic Ocean. An area of maximum precipitation exists in front of the Norwegian Lofoten islands. One aim of the LOFZY field campaign was to clarify the role cyclones play in the interaction of ocean and atmosphere. In order to obtain a comprehensive dataset of cyclone activity and ocean-atmosphere interaction a field experiment was carried out in the Lofoten region during March and April 2005. Employed platforms were the Irish research vessel RV Celtic Explorer which conducted a meteorological (radiosondes, standard parameters, observations) and an oceanographic (CTD) program. The German research aircraft Falcon accomplished eight flight missions (between 4-21 March) to observe synoptic conditions with high spatial and temporal resolution. In addition 23 autonomous marine buoys were deployed in advance of the campaign in the observed area to measure drift, air-temperature and -pressure and water-temperature. In addition to the published datasets several other measurements were performed during the experiment. Corresonding datasets will be published in the near future and are available on request. Details about all used platforms and sensors and all performed measurements are listed in the fieldreport. The following datasets are available on request: ground data at RV Celtic Explorer

  • The Fram Strait Cyclone Experiment, FRAMZY 1999, took place in the Fram Strait and Greenland Sea region during April 1999. Using aircraft, ice buoys, ship and satellite measurements a data set was compiled to investigate the properties of Fram Strait cyclones, their cyclogenetic conditions on the large- and meso-scale, and their local effects on sea ice drift and sea ice distribution and, thus, on the freshwater flow through the Fram Strait. The data were used for validation of cyclone simulations with coupled mesoscale models of the atmosphere-ice-ocean system. FRAMZY 1999 was the first one in a series of five field experiments (2002,2007,2008,2009) carried out in the frame of the Collaborative Research Centre 512 (Cyclones and the North Atlantic Climate System) funded by the German Science Foundation. In addition to the published datasets several other measurements were performed during the experiment. Corresonding datasets will be published in the near future and are available on request. Details about all used platforms and sensors and all performed measurements are listed in the fieldreport. The following datasets are available on request: ground data at RV Valdivia

  • The FRAMZY 2008 experiment aimed at the measurement of the sea ice drift in the Fram Strait and its relation to the atmospheric forcing, primarily to that by cyclones. FRAMZY 2008 was the fourth experiment with this objective and followed the FRAMZY experiments in 1999, 2002 and 2007. On 20 January 2008, seven CALIB (Compact Air-Launch Ice Buoys) buoys were deployed from a transport aircraft in a regular array of 200 km by 100 km size centered at 82.6¿N, 1.0¿E in the northern part of Fram Strait. Buoys measured autonomously air pressure, temperature and position at approximately one-hourly intervals and transmitted the data via the Argos satellite system. The lifetime of the buoys before they were lost at the ice edge or due to the breaking of ice was between 7 and 39 days (final date 28 February 2008). The southernmost position reached by a buoy after 39 days was 76.2¿N, -12.0¿E, corresponding to an average drift speed of 16.9 km per day or 0.20 ms-1. During the FRAMZY 2008 period eight cyclones passed through Fram Strait. The paper presents details of the ice motion and the atmospheric conditions. In the appendix 12-hourly maps of sea-level pressure and surface air temperature as analysed by the ECMWF, daily maps of ice concentration and daily NOAA satellite images are presented.

  • Aerosols originating from volcanic emissions have an impact on the climate: sulfate and ash particles from volcanic emissions reflect solar radiation, act as cloud condensation and ice nuclei, and modify the radiative properties and lifetime of clouds, and therefore influence the precipitation cycle. These volcanic particles can also have an impact on environmental conditions and could be very dangerous for aircraft in flight. In addition to the routine measurements, further EARLINET observations are devoted to monitor volcano eruptions. The EARLINET volcanic dataset includes extended observations related to two different volcanoes in Europe Mt. Etna (2001 and 2002 eruptions), and the Eyjafjallajökull volcano in Iceland (April - May 2010 eruption). This dataset includes also events of volcanic eruptions in the North Pacific region (2008-2010) that emitted sulfuric acid droplets into the upper troposphere lower stratosphere (UTLS) height region of the northern hemisphere. The EARLINET volcanic observations in the UTLS are complemented by the long-term stratospheric aerosol observations collected in the Stratosphere category.