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Christian Werner

Abstract

A method for developing and constructing a cloud cover indicator system is described.

The method involves pointing an IR radiometer vertically downward to a movable mirror and measuring the reflected sky radiation by comparing the difference in thermal radiance between clouds and the sky.

To determine cloud cover it is only important to have a threshold value for the clear sky. A value for the coverage is produced by a sunning system summation of all signal lengths of one cycle.

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Victor A. Banakh, Igor’N. Smalikho, Friedrich Köpp, and Christian Werner

Abstract

The results of a theoretical and experimental study of the feasibility of the turbulent energy dissipation rate ε T measurements with a continuous wave (CW) CO2 Doppler lidar in the atmospheric boundary layer are presented. Three methods of probing ε T are considered: 1) Doppler spectrum width, 2) the temporal spectrum (temporal structure function) of wind velocity measured by the Doppler lidar, and 3) spatial structure function. In these methods, information on the dissipation rate is extracted by means of analysis of the corresponding statistical characteristics of wind velocity in the inertial subrange of the turbulence, taking into account the spatial averaging of the measured wind velocity fluctuations over sounded volume.

In the first and third methods, the spatial structure of the turbulence is analyzed directly. In the second method, to determine ε T from the measured temporal characteristics, it is necessary to use a model for the spatiotemporal correlation function of wind velocity. As a result of the study, it has been shown that in the case of large longitudinal size of sounded volume and weak side wind, Taylor’s hypothesis of “frozen” turbulence cannot be accepted for the correlation function. The strict limitation on the longitudinal size of the sounded volume and therefore sounding height is the main restriction of the first method. The third method is free of such limitations. It allows one to obtain the information on the dissipation rate profile throughout the entire boundary layer. Comparison of the developed theory for statistical characteristics of wind velocity measured by the Doppler lidar with the obtained experimental data has demonstrated their good agreement.

The vertical profiles of the turbulent energy dissipation rate retrieved from Doppler lidar data with the use of the methods described above do not contradict the known experimental results. This fact confirms the feasibility of application of lidar remote sensing methods to the study of the small-scale turbulence in the atmospheric boundary layer.

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Ines Leike, Jürgen Streicher, Christian Werner, Viktor Banakh, Igor Smalikho, Werner Wergen, and Alexander Cress

Abstract

Doppler lidars measure the range-resolved line-of-sight wind component by extracting the Doppler shift of radiation backscattered from atmospheric aerosols and molecules. A virtual instrument was developed to simulate wind measurements by flying virtually over the atmosphere. The atmosphere contains all components that influence the lidar, that is, wind, turbulence, aerosols, clouds, etc. For a selected time period, a dataset of the atmospheric conditions from the global model and the local model was provided by the German Weather Service. Three different Doppler lidar systems were simulated for this report: a coherent airborne conical scanning 10-μm Doppler lidar, a 10-μm and a 2-μm spaceborne system, and a spaceborne incoherent ultraviolet Doppler lidar.

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Oliver Reitebuch, Christian Werner, Ines Leike, Patricia Delville, Pierre H. Flamant, Alexander Cress, and Dirk Engelbart

Abstract

The airborne Wind Infrared Doppler Lidar (WIND) has been developed through French–German cooperation. The system is based on a pulsed 10.6-μm laser transmitter, a heterodyne receiver, and a conical scanning device. To the authors' knowledge, it is the first airborne Doppler lidar for atmospheric research to retrieve the whole tropospheric wind profile between the ground and the flight level looking downward. The wind vector is measured with the velocity-azimuth display (VAD) technique with a vertical sampling of 250 m. The first flights on board the DLR Falcon 20 aircraft were performed in 1999. Results of a comparison among WIND, radiosondes, wind-profiler radar measurements, numerical models, and simulations are presented. It is shown that the correspondence of airborne WIND measurements with those of other instruments or models is better than 1.5 m s−1 and 5° for the horizontal wind vector. These results show the excellent capability of conical scanning Doppler lidars to provide unique insights into mesoscale dynamic processes and progress made toward future spaceborne systems.

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Sophie Bastin, Philippe Drobinski, Vincent Guénard, Jean-Luc Caccia, Bernard Campistron, Alain M. Dabas, Patricia Delville, Oliver Reitebuch, and Christian Werner

Abstract

The three-dimensional structure and dynamics of the combination of the sea breeze and the mistral at the Rhône Valley exit, in southeastern France, have been investigated experimentally and numerically on 22 June 2001. The mistral refers to a severe northerly wind that develops along the Rhône Valley. The exit of this valley is located near the Mediterranean Sea where sea-breeze circulation often develops. The sea breeze and the mistral coexist this day because of the weakness of this mistral event.

The event was documented in the framework of the Expérience sur Site pour Contraindre les Modèles de Pollution Atmosphérique et de Transport d'Emissions (ESCOMPTE) field experiment. Several important data sources are used (airborne Doppler lidar, UHF wind profilers, radiosoundings, and surface stations) as well as nonhydrostatic mesoscale simulations.

This paper examines the various mechanisms that drive the time and spatial variability of the mistral and the sea breeze in various regions of the Rhône Valley. In the morning, the sea breeze penetrates inland near the western side of the Rhône Valley then moves back because of the reinforcement of the mistral flow caused by the deepening of the leeward surface low due to convection at noon. At midday, the sea breeze penetrates inland in the middle of the Rhône Valley only. In contrast to pure sea-breeze episodes when the sea breeze can extend inland over a horizontal range of more than 150 km, the presence of the mistral prevents the sea breeze from penetrating more than 40 km onshore. In the late afternoon, the sea breeze reaches the eastern side of the Rhône Valley but over a smaller horizontal range because of higher local topography and because the mistral is more intense in this part of the Rhône Valley.

The situations of sea-breeze–mistral interactions can have a severe impact on regional air quality. Indeed, the southerly sea breeze, which advects toward the countryside the pollutants emitted from the large coastal city of Marseille, France, and its industrialized suburbs, cannot penetrate far inland because of the mistral blowing in the opposite direction. This leads to the stagnation of the pollutants near the area of emission that is also the most densely inhabited area of the region (over one million inhabitants).

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Christiane Voigt, Ulrich Schumann, Andreas Minikin, Ahmed Abdelmonem, Armin Afchine, Stephan Borrmann, Maxi Boettcher, Bernhard Buchholz, Luca Bugliaro, Anja Costa, Joachim Curtius, Maximilian Dollner, Andreas Dörnbrack, Volker Dreiling, Volker Ebert, Andre Ehrlich, Andreas Fix, Linda Forster, Fabian Frank, Daniel Fütterer, Andreas Giez, Kaspar Graf, Jens-Uwe Grooß, Silke Groß, Katharina Heimerl, Bernd Heinold, Tilman Hüneke, Emma Järvinen, Tina Jurkat, Stefan Kaufmann, Mareike Kenntner, Marcus Klingebiel, Thomas Klimach, Rebecca Kohl, Martina Krämer, Trismono Candra Krisna, Anna Luebke, Bernhard Mayer, Stephan Mertes, Sergej Molleker, Andreas Petzold, Klaus Pfeilsticker, Max Port, Markus Rapp, Philipp Reutter, Christian Rolf, Diana Rose, Daniel Sauer, Andreas Schäfler, Romy Schlage, Martin Schnaiter, Johannes Schneider, Nicole Spelten, Peter Spichtinger, Paul Stock, Adrian Walser, Ralf Weigel, Bernadett Weinzierl, Manfred Wendisch, Frank Werner, Heini Wernli, Martin Wirth, Andreas Zahn, Helmut Ziereis, and Martin Zöger

Abstract

The Midlatitude Cirrus experiment (ML-CIRRUS) deployed the High Altitude and Long Range Research Aircraft (HALO) to obtain new insights into nucleation, life cycle, and climate impact of natural cirrus and aircraft-induced contrail cirrus. Direct observations of cirrus properties and their variability are still incomplete, currently limiting our understanding of the clouds’ impact on climate. Also, dynamical effects on clouds and feedbacks are not adequately represented in today’s weather prediction models.

Here, we present the rationale, objectives, and selected scientific highlights of ML-CIRRUS using the G-550 aircraft of the German atmospheric science community. The first combined in situ–remote sensing cloud mission with HALO united state-of-the-art cloud probes, a lidar and novel ice residual, aerosol, trace gas, and radiation instrumentation. The aircraft observations were accompanied by remote sensing from satellite and ground and by numerical simulations.

In spring 2014, HALO performed 16 flights above Europe with a focus on anthropogenic contrail cirrus and midlatitude cirrus induced by frontal systems including warm conveyor belts and other dynamical regimes (jet streams, mountain waves, and convection). Highlights from ML-CIRRUS include 1) new observations of microphysical and radiative cirrus properties and their variability in meteorological regimes typical for midlatitudes, 2) insights into occurrence of in situ–formed and lifted liquid-origin cirrus, 3) validation of cloud forecasts and satellite products, 4) assessment of contrail predictability, and 5) direct observations of contrail cirrus and their distinction from natural cirrus. Hence, ML-CIRRUS provides a comprehensive dataset on cirrus in the densely populated European midlatitudes with the scope to enhance our understanding of cirrus clouds and their role for climate and weather.

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