C. Forster

Norwegian Institute for Air Research, Kristiania (historical), Oslo County, Norway

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Publications (124)159.61 Total impact

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    1st ECATS Conference; 11/2013
  • 13th EMS Annual Meeting & 11th ECAM; 09/2013
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    Dennis Stich, Caroline Forster, Arnold Tafferner
    06/2013;
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    ABSTRACT: In this paper, recent changes to the Meteosat thunderstorm TRacking And Monitoring algorithm (Cb-TRAM) are presented as well as a validation of Cb-TRAM against data from the European ground-based LIghtning NETwork (LINET) of Nowcast GmbH and the South African Weather Service Lightning Detection Network (SAWS LDN). Validation is conducted along the well-known skill measures probability of detection (POD) and false alarm ratio (FAR) on the basis of Meteosat/SEVIRI pixels as well as on the basis of thunderstorm objects. The values obtained demonstrate specific limitations of Cb-TRAM, as well as limitations of satellite methods in general which are based on thermal emission and solar reflectivity information from thunderstorm cloud tops. Although the climatic conditions and the occurrence of thunderstorms are quite different for Europe and South Africa, quality score values are similar. Our conclusion is that Cb-TRAM provides robust results of well-defined quality for very different climatic regimes. The POD for a thunderstorm with intense lightning is about 80% during the day. The FAR for a Cb-TRAM detection which is not even close to intense lightning is about 50%. If only proximity to any lightning activity is required, FAR is much lower at about 15%. Pixel-based analysis shows that detected thunderstorm object size is not indiscriminately large, but well within physical limitations of the satellite method. Night-time POD and FAR are somewhat worse as the detection scheme does not use the high-resolution visible information during night-time hours. Nowcasting scores show useful values up to approximately 30 min in advance.
    Atmospheric Measurement Techniques 06/2013; 6(6):1567-1583. · 3.21 Impact Factor
  • Arnold Tafferner, Caroline Forster
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    ABSTRACT: Within the project Distributed Research Infrastructure for Hydro-Meteorology (DRIHM) DLR is involved with its nowcasting tools Cb-TRAM and Rad-TRAM. Cb-TRAM (thunderstorm Tracking And Monitoring) is a fully automated tracking and nowcasting algorithm. Intense convective cells are detected, tracked and discriminated with respect to onset, rapid development, and mature phase. In addition, short range forecasts are provided. The detection is based on Meteosat SEVIRI data by combining four selected channels. Areas of convection initiation, of rapid vertical development, and mature thunderstorm cells are identified. The tracking is based on geographical overlap between current detections and first guess patterns of cells detected in preceding time steps. Based on a so-called pyramid matcher also nowcasts of motion and development of detected areas are provided. In contrast to Cb-TRAM, the tool Rad-TRAM (Radar Tracking And Monitoring) operates with radar data (regional or composite) with the aim to detect areas of heavy precipitation. Both trackers can be run both on observed and model generated (synthetic) data. Examples of tracking and nowcasting of severe convection are presented, including the Genoa flood of 4 November 2011.
    04/2013;
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    ABSTRACT: In this manuscript, recent changes to the DLR METEOSAT thunderstorm TRacking And Monitoring algorithm (Cb-TRAM) are presented as well as a validation of Cb-TRAM against the European ground-based LIghtning NETwork data (LINET) of Nowcast GmbH and Lightning Detection Network (LDN) data of the South African Weather Service (SAWS). The validation is conducted along the well known skill scores probability of detection (POD) and false alarm ratio (FAR) on the basis of METEOSAT/SEVIRI pixels as well as on the basis of thunderstorm objects. The values obtained demonstrate the limits of Cb-TRAM in specific as well as the limits of satellite methods in general which are based on thermal emission and solar reflectivity information from thunderstorm tops. Although the climatic conditions and the occurence of thunderstorms is quite different for Europe and South Africa, the quality score values are similar. Our conclusion is that Cb-TRAM provides robust results of well-defined quality for very different climatic regimes. The POD for a thunderstorm with intense lightning is about 80% during the day. The FAR for a Cb-TRAM detected thunderstorm which is not at least close to intense lightning activity is about 50%; if the proximity to any lightning activity is evaluated the FAR is even much lower at about 15%. Pixel-based analysis shows that the detected thunderstorm object size is not indiscriminately large, but well within the physical limitations of the method. Nighttime POD and FAR are somewhat worse as the detection scheme can not use high resolution visible information. Nowcasting scores show useful values up to approximatelly 30 min.
    Atmospheric Measurement Techniques Discussions. 02/2013; 6(1):1269-1310.
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    ABSTRACT: Near-real-time in-flight weather services for business and regional aviation are nowadays quite well developed in USA, but still very limited in Europe due to the lack of equivalent infrastructure and service offer. The operators of the business and regional aviation in Europe would strongly benefit from in-flight weather forecasting and trajectory tracking in order to fly safely and to optimise the trajectory. On the other hand, weather agencies would greatly benefit from weather observations provided by regional and business aviation (e.g. temperature and wind speed data collected by the aircraft sensors, nowadays delivered only by commercial airlines in the framework of AMDAR) as they would drastically increase geographical coverage and number of measurement thanks to different routes w.r.t. commercial airlines.
    Integraded Communications Navigation and Surveillance; 01/2013
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    ABSTRACT: The operators of the business and regional aviation in Europe would strongly benefit from inflight weather forecasting and trajectory tracking in order to fly safely and to optimise the trajectory. On the other hand, weather agencies would greatly benefit from weather observations provided by regional and business aviation (e.g. temperature and wind speed data collected by the aircraft sensors, nowadays delivered only by commercial airlines in the framework of AMDAR) as they would drastically increase geographical coverage and number of measurement thanks to different routes w.r.t. commercial airlines. Near-real-time in-flight weather services for business and regional aviation are nowadays quite well developed in USA, but still very limited in Europe due to the lack of equivalent infrastructure and service offer. Thus, the PLANET-2 project, co-funded by the European Space Agency (ESA) and led by ATMOSPHERE-F (F) with ATMOSPHERE-D (G), DLR (G), TRIAGNOSYS (G) and METEO-FRANCE (F), aims at developing a commercially sustainable in-flight weather service based on integrated space assets (i.e. SatCom and Navigation, with the support of Earth Observation data for some of the weather products) and terrestrial wireless networks (e.g. GPRS, 3G, 4G) to reduce service costs. The paper presents the main results of the work carried out to meet the PLANET-2 requirements.
    Integrated Communications, Navigation and Surveillance Conference (ICNS), 2013; 01/2013
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    Caroline Forster, Arnold Tafferner
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    ABSTRACT: The successful demonstration and assessment of the DLR thunderstorm nowcasting algorithms at Munich Airport during two campaigns in the summers of 2010 and 2011 are described. The algorithms Cb-TRAM and Rad-TRAM, that detect, monitor, and forecast up to one hour (nowcast) thunderstorm cells from satellite and radar data, run in real time and provided new thunderstorm products for users at the airport. The products were presented on displays the users were already familiar with as well as on webpages designed by DLR. On the webpages, also additional information like measurements with DLR’s polarimetric radar and model forecasts was shown. Moreover, thunderstorm warnings were is-sued and sent via email to the users whenever a thunderstorm was detected in the terminal manoeu-vring area of the airport of Munich. The nowcasting skills of Rad-TRAM and Cb-TRAM are encouraging, especially for lead times up to 30 minutes, and the user feedback on the DLR thunderstorm products was very positive. The Rad-TRAM and Cb-TRAM products provide a good overview on the situation and its future development, and the thunderstorm warnings were very helpful for the collaborative decision making at the airport. However, some suggestions for improvements were made like the demand for nowcasts beyond one hour. This will be considered within the integrated weather forecast system, WxFUSION, which has been further developed during the campaigns.
    The DLR Project Wetter & Fliegen. 02/2012;
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    Thomas Gerz, Caroline Forster, Arnold Tafferner
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    ABSTRACT: Thunderstorms are top-ranked by pilots as weather situations compromising the flight safety. The information for pilots about adverse weather like thunderstorms today is, if at all, based on significant weather charts. Such services, however, do not give the required information for a particular flight in a particular circumstance because thunderstorms are relatively short-living phenomena. Information is required in the time-scale of up to about one hour with frequent updates clearly outlining the dangerous areas which should be avoided. Tools and products are descried which deliver that information tailored along the aircraft’s trajectory. The information is produced on ground by weather expert systems and delivered to and stored in a ground-based weather processor which serves as a data base and interface between the expert system and the aircraft. Concepts and first tests are described where the information on thunderstorms is up-linked from the data base to the aircraft.
    The DLR Project Wetter & Fliegen. 02/2012;
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    Arnold Tafferner, Caroline Forster, Thomas Gerz
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    ABSTRACT: The meteorological network of observation and prediction continuously delivers an enormous amount of various atmospheric parameters. In particular in the area of an aerodrome the observation density is typically higher than on average. In the project we spawned the idea to smartly concatenate the variety of available data which are relevant for aviation and develop new products which use the information contained in the data but describe the phenomenon of interest in a simple and unambiguous way for direct use for the aviation stakeholders. We developed this idea in a concept and related system named WxFUSION, meaning “weather forecast user-oriented system including object nowcasting”.
    DLR Deutsches Zentrum fur Luft- und Raumfahrt e.V. - Forschungsberichte 02/2012;
  • Arnold Tafferner, Caroline Forster
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    ABSTRACT: This article is about present weather and its immediate development, on the challenge of how to observe it, and how to forecast it in the short term. It touches on the problems meteorologists have in delivering reliable estimates of, e.g., which path a thunderstorm will take during its track, whether it will bring hail or just rain, or when there will be freezing conditions at an airport with subsequent problems for air traffic on ground, arrival and departure. Some illustrative examples are given, showing how the problems are tackled and how integrated forecasting systems, in particular, can be successful in meeting the challenge.
    Atmospheric Physics: Background - Methods - Trends. 01/2012;
  • 63rd International Astronautical Congress, Naples; 01/2012
  • Toulouse Space Show; 01/2012
  • Thomas Gerz, Caroline Forster, Arnold Tafferner
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    ABSTRACT: Weather has a significant impact on the safety and efficiency of air traffic during all phases of flight. Especially information on adverse weather must be tailored to the user's needs, easy to understand, self-explaining and clear in its message. DLR-IPA has developed a concept and tools to detect, track and predict hazardous weather elements and provide this information in simple unambiguous form to controllers and pilots. It has been demonstrated that these products make a significant contribution to raising the safety and efficiency of the air transport system.
    Atmospheric Physics: Background - Methods - Trends. 01/2012;
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    ECSS 2011 - 6th European Conference on Severe Storms; 05/2011
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    ABSTRACT: Airborne lidar and in-situ measurements of aerosols and trace gases were performed in volcanic ash plumes over Europe between Southern Germany and Iceland with the Falcon aircraft during the eruption period of the Eyjafjalla volcano between 19 April and 18 May 2010. Flight planning and measurement analyses were supported by a refined Meteosat ash product and trajectory model analysis. The volcanic ash plume was observed with lidar directly over the volcano and up to a distance of 2700 km downwind, and up to 120 h plume ages. Aged ash layers were between a few 100 m to 3 km deep, occurred between 1 and 7 km altitude, and were typically 100 to 300 km wide. Particles collected by impactors had diameters up to 20 m diameter, with size and age dependent composition. Ash mass concentrations were derived from optical particle spectrometers for a particle density of 2.6 g cm-3 and various values of the refractive index (RI, real part: 1.59; 3 values for the imaginary part: 0, 0.004 and 0.008). The mass concentrations, effective diameters and related optical properties were compared with ground-based lidar observations. Theoretical considerations of particle sedimentation constrain the particle diameters to those obtained for the lower RI values. The ash mass concentration results have an uncertainty of a factor of two. The maximum ash mass concentration encountered during the 17 flights with 34 ash plume penetrations was below 1 mg m-3. The Falcon flew in ash clouds up to about 0.8 mg m-3 for a few minutes and in an ash cloud with approximately 0.2 mg m-3 mean-concentration for about one hour without engine damage. The ash plumes were rather dry and correlated with considerable CO and SO2 increases and O3 decreases. To first order, ash concentration and SO2 mixing ratio in the plumes decreased by a factor of two within less than a day. In fresh plumes, the SO2 and CO concentration increases were correlated with the ash mass concentration. The ash plumes were often visible slantwise as faint dark layers, even for concentrations below 0.1 mg m-3. The large abundance of volatile Aitken mode particles suggests previous nucleation of sulfuric acid droplets. The effective diameters range between 0.2 and 3 µm with considerable surface and volume contributions from the Aitken and coarse mode aerosol, respectively. The distal ash mass flux on 2 May was of the order of 500 (240-1600) kg s-1. The volcano induced about 10 (2.5-50) Tg of distal ash mass and about 3 (0.6-23) Tg of SO2 during the whole eruption period. The results of the Falcon flights were used to support the responsible agencies in their decisions concerning air traffic in the presence of volcanic ash.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 02/2011; 11(2011):2245-2279. · 5.51 Impact Factor
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    Nikolai Dotzek, Caroline Forster
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    ABSTRACT: Severe thunderstorms constitute a major weather hazard in Europe, with an estimated total damage of € 5-8 billion each year. Yet a pan-European database of severe weather reports in a homogeneous data format has become available only recently: the European Severe Weather Database (ESWD). We demonstrate the large potential of ESWD applications for storm detection and forecast evaluation purposes. The study of six warm-season severe weather days in Europe from 2007 and 2008 revealed that up to 47% of the ESWD reports were located exactly within the polygons detected by the Cb-TRAM algorithm for three different stages of deep moist convection. The cool-season case study of extratropical cyclone “Emma” on 1 March 2008 showed that low-topped winter thunderstorms provide a challenge for satellite storm detection and nowcasting adapted to warm-season storms with high, cold cloud tops. However, this case also demonstrated how ESWD reports alone can still be valuable to identify the hazardous regions along the cold front of the cyclone. The analysis of all warm-season (JJA) severe weather days in Europe in 2008 corroborated these findings. There is good agreement between ESWD reports and Cb-TRAM detected thunderstorms, even though no exact correspondence between ESWD reports and Cb-TRAM cells is required (e.g., due to storm morphology). Correspondingly, a large portion of ESWD reports regarded as misses by our strict in/out-of-Cb-TRAM-polygon criterion were still located close to a Cb-TRAM cell. Quantitatively, only the probability of detection (POD) can be evaluated due to the different characteristics of the two data sources. For the JJA 2008 period, the POD for storm detection was 0.24 on average, with maximum values up to 0.58. The respective analysis for the 30 and 60 minutes nowcasts yielded average POD values of 0.11 and 0.08, respectively, with maximum values of POD exceeding 0.4 on three different days for the 30 minutes nowcast and on one day for the 60 minutes nowcast.
    Atmospheric Research 01/2011; online(2011). · 2.20 Impact Factor
  • A. Tafferner, C. Forster, T. Zinner
    EMS Annual Meeting; 01/2011
  • Integration and Operations (ATIO) Conference; 01/2011