Showing papers by "Matthias Wiegner published in 2008"

Systematic lidar observations of Saharan dust over Europe in the frame of EARLINET (2000-2002)

Abstract: [1] More than 130 observation days of the horizontal and vertical extent of Saharan dust intrusions over Europe during the period May 2000 to December 2002 were studied by means of a coordinated lidar network in the frame of the European Aerosol Research Lidar Network (EARLINET). The number of dust events was greatest in late spring, summer, and early autumn periods, mainly in southern (S) and southeastern (SE) Europe. Multiple aerosol dust layers of variable thickness (300–7500 m) were observed. The center of mass of these layers was located in altitudes between 850 and 8000 m. However, the mean thickness of the dust layer typically stayed around 1500–3400 m and the corresponding mean center of mass ranged from 2500 to 6000 m. In exceptional cases, dust aerosols reached northwestern (NW), northern (N), or northeastern (NE) Europe, penetrating the geographical area located between 4°W–28°E (longitude) and 38°N–58°N (latitude). Mean aerosol optical depths (AOD), extinction-to-backscatter ratios (lidar ratios, LR), and linear depolarization ratios of desert aerosols ranged from 0.1 to 0.25 at the wavelength of 355 or 351 nm, 30 to 80 sr at 355 or 351 nm, and 10 to 25% at 532 nm, respectively, within the lofted dust plumes. In these plumes typical Saharan dust backscatter coefficients ranged from 0.5 to 2 Mm−1sr−1. Southern European stations presented higher variability of the LR values and the backscatter-related Angstrom exponent values (BRAE) (LR: 20–100 sr; BRAE: −0.5 to 3) than northern ones (LR: 30–80 sr; BRAE: −0.5 to 1).

Influence of Saharan dust on cloud glaciation in southern Morocco during the Saharan Mineral Dust Experiment

Abstract: [1] Multiwavelength lidar, Sun photometer, and radiosonde observations were conducted at Ouarzazate (30.9°N, 6.9°W, 1133 m above sea level, asl), Morocco, in the framework of the Saharan Mineral Dust Experiment (SAMUM) in May–June 2006. The field site is close to the Saharan desert. Information on the depolarization ratio, backscatter and extinction coefficients, and lidar ratio of the dust particles, estimates of the available concentration of atmospheric ice nuclei at cloud level, profiles of temperature, humidity, and the horizontal wind vector as well as backward trajectory analysis are used to study cases of cloud formation in the dust with focus on heterogeneous ice formation. Surprisingly, most of the altocumulus clouds that form at the top of the Saharan dust layer, which reaches into heights of 4–7 km asl and has layer top temperatures of −8°C to −18°C, do not show any ice formation. According to the lidar observations the presence of a high number of ice nuclei (1–20 cm−3) does not automatically result in the obvious generation of ice particles, but the observations indicate that cloud top temperatures must typically reach values as low as −20°C before significant ice production starts. Another main finding is that liquid clouds are obviously required before ice crystals form via heterogeneous freezing mechanisms, and, as a consequence, that deposition freezing is not an important ice nucleation process. An interesting case with cloud seeding in the free troposphere above the dust layer is presented in addition. Small water clouds formed at about −30°C and produced ice virga. These virga reached water cloud layers several kilometers below the initiating cloud cells and caused strong ice production in these clouds at temperatures as high as −12°C to −15°C.

Vertical aerosol profiles from Raman polarization lidar observations during the dry season AMMA field campaign

Abstract: [1] Lidar measurements of the vertical distribution of optical particle properties were performed in January 2006 in the frame of the dry season field experiment of the African Monsoon Multidisciplinary Analyses (AMMA) The measurements were conducted at a remote site in West Africa in the Sahel region just south of the Saharan desert to investigate the influence of particles on the West African monsoon The portable Raman polarization lidar system POLIS of the University of Munich was operated each forenoon and during selected nights These measurements are the first Raman and depolarization lidar measurements taken in the Sahel The particle depolarization ratio and the extinction coefficient profiles allow the characterization of the particles and the distinction between Saharan dust particles and biomass burning aerosol (BBA) The origin of this aerosol was investigated by trajectory analyses The profiles show a varying dust layer in the lowermost troposphere during the whole period Above the dust layer a broad layer of BBA reaching up to an altitude of 5 km was frequently observed The extinction coefficient in the dust layer was between 02 and 04 km−1 at 355 nm, and the particle depolarization was around 25% In the BBA layer the extinction coefficient was lower with values between 01 and 02 km−1, and the particle depolarization ratio was below 10% Lidar ratio values around 55 sr were found for the dust layer and around 75 sr for the BBA layer From previous observations, lidar ratios between 40 and 80 sr were expected for BBA

The general observation period 2007 within the priority program on quantitative precipitation forecasting: concept and first results

Abstract: In the year 2007 a General Observation Period (GOP) has been performed within the German Priority Program on Quantitative Precipitation Forecasting (PQP). By optimizing the use of existing instrumentation a large data set of in-situ and remote sensing instruments with special focus on water cycle variables was gathered over the full year cycle. The area of interest covered central Europe with increasing focus towards the Black Forest where the Convective and Orographically-induced Precipitation Study (COPS) took place from June to August 2007. Thus the GOP includes a variety of precipitation systems in order to relate the COPS results to a larger spatial scale. For a timely use of the data, forecasts of the numerical weather prediction models COSMO-EU and COSMO-DE of the German Meteorological Service were tailored to match the observations and perform model evaluation in a near real-time environment. The ultimate goal is to identify and distinguish between different kinds of model deficits and to improve process understanding.

The European Aerosol Research Lidar Network (EARLINET): An Overview

Abstract: The European Aerosol Research LIdar NETwork (EARLINET) is the first aerosol lidar network on a continental scale with the main goal to provide a comprehensive, quantitative, and statistically significant database for the aerosol distribution over Europe. Next, we present EARLINET along with the main network activities.