Holger Baars
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Featured researches published by Holger Baars.
Geophysical Research Letters | 2009
Albert Ansmann; Holger Baars; Matthias Tesche; Detlef Müller; Dietrich Althausen; Ronny Engelmann; Theotonio Pauliquevis; Paulo Artaxo
[1] Quasi-simultaneous vertically resolved multiwavelength aerosol Raman lidar observations were conducted in the near field (Praia, Cape Verde, 15°N, 23.5°W) and in the far field (Manaus, Amazon basin, Brazil, 2.5°S, 60°W) of the long-range transport regime between West Africa and South America. Based on a unique data set (case study) of spectrally resolved backscatter and extinction coefficients, and of the depolarization ratio a detailed characterization of aerosol properties, vertical stratification, mixing, and aging behavior during the long-distance travel in February 2008 (dry season in western Africa, wet season in the Amazon basin) is presented. While highly stratified aerosol layers of dust and smoke up to 5.5 km height were found close to Africa, the aerosol over Manaus was almost well-mixed, reached up to 3.5 km, and mainly consisted of aged biomass burning smoke.
Geophysical Research Letters | 2014
Thomas Kanitz; Ronny Engelmann; Bernd Heinold; Holger Baars; Annett Skupin; A. Ansmann
Saharan dust was observed with shipborne lidar from 60° to 20°W along 14.5°N during a 1-month transatlantic cruise of the research vessel Meteor. About 4500 km off the coast of Africa, mean extinction and backscatter-related Angstrom exponent of 0.1, wavelength-independent extinction-to-backscatter ratios (lidar ratios) of around 45 sr, and particle linear depolarization ratio of 20% were found for aged dust (transport time >10 days). In contrast, dust with a shorter atmospheric residence time of 2–3 days showed Angstrom exponents of −0.5 (backscatter coefficient) and 0.1 (extinction coefficient), mean lidar ratios of 64 and 50 sr, and particle linear depolarization ratios of 22 and 26% at 355 and 532 nm wavelength, respectively. Traces of fire smoke were also detected in the observed dust layers. The lidar observations were complemented by Aerosol Robotic Network handheld Sun photometer measurements, which revealed a mean total atmospheric column aerosol optical thickness of 0.05 for pure marine conditions (in the absence of lofted aerosol layers) and roughly 0.9 during a strong Saharan dust outbreak. The achieved data set was compared with first Consortium for Small Scale Modeling-Multi-Scale Chemistry Aerosol Transport simulations. The simulated vertical aerosol distribution showed good agreement with the lidar observations.
Journal of Geophysical Research | 2014
Jörg Schmidt; Albert Ansmann; Johannes Bühl; Holger Baars; Ulla Wandinger; Detlef Müller; Aleksey V. Malinka
Date of Acceptance: 24/04/2014 This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made
Lidar Technologies, Techniques, and Measurements for Atmospheric Remote Sensing IX | 2013
Dietrich Althausen; Ronny Engelmann; Holger Baars; Birgit Heese; Thomas Kanitz; M. Komppula; Eleni Giannakaki; A. Pfüller; Ana Maria Silva; Jana Preißler; Frank Wagner; Juan Luis Guerrero Rascado; S. N. Pereira; Jae-Hyun Lim; Joon Young Ahn; Matthias Tesche; Iwona S. Stachlewska
PollyNET is a growing global network of automatized multiwavelength polarization Raman lidars of type Polly (Althausen et al., 2009). The goal of this network is to conduct advanced remote measurements of aerosol profiles and clouds by the same type of instrument. Since 2006 this network assists the controlling and adjustment activities of Polly systems. A central facility receives the data from the Polly measurements. The observational data are displayed in terms of quicklooks at http://polly:tropos.de in near real time. In this way, the network serves as a central information platform for inquisitive scientists. PollyNET comprises permanent stations at Leipzig (Germany), Kuopio (Finland), Evora (Portugal), Baengnyeong Island (South Korea), Stockholm (Sweden), and Warsaw (Poland). Non-permanent stations have been used during several field experiments under both urban and very remote conditions - like the Amazon rainforest. These non-permanent stations were lasting from several weeks up to one year and have been located in Brazil, India, China, South Africa, Chile, and also aboard the German research vessels Polarstern and Meteor across the Atlantic. Within PollyNET the interaction and knowledge exchange is encouraged between the Polly operators. This includes maintenance support in system calibration procedures and distribution of latest hardware and software improvements. This presentation introduces the PollyNET. Main features of the Polly systems will be presented as well as recent instrumental developments. Some measurement highlights achieved within PollyNET are depicted.
Remote Sensing of Clouds and the Atmosphere XVIII; and Optics in Atmospheric Propagation and Adaptive Systems XVI | 2013
Johannes Bühl; Patric Seifert; Ulla Wandinger; Holger Baars; Thomas Kanitz; Jörg Schmidt; Alexander Myagkov; Ronny Engelmann; Annett Skupin; Birgit Heese; André Klepel; Dietrich Althausen; A. Ansmann
The study of interactions between aerosol particles, atmospheric dynamics and clouds and their resulting corresponding indirect effects on precipitation and radiative transfer demand new measurement strategies combining the strength of lidar, radar, and in-situ instrumentation. To match this challenge the Leipzig Aerosol and Cloud Remote Observations System (LACROS) has been set up at TROPOS, combining the strengths of a unique set of active and passive remote sensing and in-situ measurement systems.
Journal of Geophysical Research | 2014
Zhenyi Chen; Wenqing Liu; Birgit Heese; Dietrich Althausen; Holger Baars; Tianhai Cheng; Xiaowen Shu; Tianshu Zhang
We present combined Raman and elastic backscatter lidar observations in Zhongshan, PRD (Pearl River Delta), China, during two periods in 2009: one haze period and one moderate pollution period. During the haze period, high Aerosol Optical Depth (AOD) (0.86 and 1.20 at 355 nm) and medium Angstrom exponents (1.23 and 1.35 at 355 nm/532 nm) were observed. In the moderate pollution period, the corresponding parameters were comparatively lower with values of 0.83 and 0.74 at 355 nm for AOD and 1.108 and 0.98 at 355 nm/532 nm for Angstrom exponent. The mean lidar ratios in the two periods were 64 ± 10 sr and 56 ± 9 sr, respectively, at 355 nm. The Angstrom exponent was calculated for the extinction from the wavelength pair 355 nm/532 nm, with high values of around 1.35 for the haze event. The particle size distribution and single-scattering albedo derived from Sun photometer measurements indicate the presence of rather small particles. The 3 day back trajectories from a Hybrid Single-Particle Lagrangian Integrated Trajectory model in the haze period indicate that the air masses in the lower layer were advected from the southeast coast of China, where incomplete combustion of carbonaceous fuels and straw burning are frequently found in Shanghai during the heating period in winter. In the moderate pollution period, the air mass passed through western China, indicating a combination of some pollution from South Asia in case of strong convection, local aerosol aging, and smoke from adjacent fire burning spots in the PRD region.
Geophysical Research Letters | 2015
Patric Seifert; Clara Kunz; Holger Baars; Albert Ansmann; Johannes Bühl; Fabian Senf; Ronny Engelmann; Dietrich Althausen; Paulo Artaxo
Based on 11 months of polarization lidar observations in the Amazon Basin near Manaus, Brazil (2.3∘S, 60∘W), the relationship between temperature and heterogeneous ice formation efficiency in stratiform clouds was evaluated in the cloud top temperature range between −40 and 0∘C. Between −30 and 0∘C, ice-containing clouds are a factor of 1.5 to 2 more frequent during the dry season. Free-tropospheric aerosol backscatter profiles revealed a twofold to tenfold increase in aerosol load during the dry season and a Monitoring Atmospheric Composition and Climate—Interim Implementation reanalysis data set implies that the aerosol composition during the dry season is strongly influenced by biomass burning aerosol, whereas other components such as mineral dust do not vary strongly between the seasons. The injection of smoke accompanied by the likely dispersion of biological material, soil dust, or ash particles was identified as a possible source for the increased ice formation efficiency during the dry season.
Optics and Photonics for Energy and the Environment | 2016
Julian Hofer; Dietrich Althausen; Sabur F. Abdullaev; Abduvosit Makhmudov; Bakhron I. Nazarov; Georg Schettler; Ronny Engelmann; Holger Baars; Bernd Heinold; K. Müller; Khanneh Wadinga Fomba
Dust influences climate and weather by direct and indirect radiative effects or heterogeneous ice nucleation. Dust is often transported to and across Tajikistan. Tajikistan and Central Asia suffer from climate change and the potential role of dust needs to be investigated. But up to now, only a small number of measurements are available in that region, especially no vertical profiles of aerosol optical properties are known. Therefore the Central Asian Dust EXperiment (CADEX) conducts first lidar measurements in Tajikistan for long-term vertically resolved aerosol measurements from March 2015–September 2016. The multiwavelength polarization Raman lidar PollyXT is used for these measurements. Two characteristic measurement examples of dust layers are presented in this contribution.
Atmospheric Chemistry and Physics | 2018
Stephanie Bohlmann; Holger Baars; Martin Radenz; Ronny Engelmann; Andreas Macke
The multi-wavelength Raman lidar PollyXT has been regularly operated aboard the research vessel Polarstern on expeditions across the Atlantic Ocean from north to south and vice versa. The lidar measurements of the RV Polarstern cruises PS95 from Bremerhaven, Germany, to Cape Town, Republic of South Africa (November 2015), and PS98 from Punta Arenas, Chile, to Bremerhaven, Germany (April/May 2016), are presented and analysed in detail. The latest set-up of PollyXT allows improved coverage of the marine boundary layer (MBL) due to an additional near-range receiver. Three case studies provide an overview of the aerosol detected over the Atlantic Ocean. In the first case, marine conditions were observed near South Africa on the autumn cruise PS95. Values of optical properties (depolarisation ratios close to zero, lidar ratios of 23 sr at 355 and 532 nm) within the MBL indicate pure marine aerosol. A layer of dried marine aerosol, indicated by an increase of the particle depolarisation ratio to about 10 % at 355 nm (9 % at 532 nm) and thus confirming the non-sphericity of these particles, could be detected on top of the MBL. On the same cruise, an almost pure Saharan dust plume was observed near the Canary Islands, presented in the second case. The third case deals with several layers of Saharan dust partly mixed with biomass-burning smoke measured on PS98 near the Cabo Verde islands. While the MBL was partly mixed with dust in the pure Saharan dust case, an almost marine MBL was observed in the third case. A statistical analysis showed latitudinal differences in the optical properties within the MBL, caused by the downmixing of dust in the tropics and anthropogenic influences in the northern latitudes, whereas the optical properties of the MBL in the Southern Hemisphere correlate with typical marine values. The particle depolarisation ratio of dried marine layers ranged between 4 and 9 % at 532 nm. Night measurements from PS95 and PS98 were used to illustrate the potential of aerosol classification using lidar ratio, particle depolarisation ratio at 355 and 532 nm, and Ångström exponent. Lidar ratio and particle depolarisation ratio have been found to be the main indicator for particle type, whereas the Ångström exponent is rather variable.
Optics and Photonics for Energy and the Environment | 2017
Julian Hofer; Dietrich Althausen; Sabur F. Abdullaev; Abduvosit Makhmudov; Bakhron I. Nazarov; Georg Schettler; Holger Baars; Ronny Engelmann; Bernd Heinold; K. Müller; K. Wadinga Fomba; Konrad Kandler; Albert Ansmann
Dust influences climate and weather by direct and indirect radiative effects or heterogeneous ice nucleation. Dust is often transported to and across Tajikistan. Tajikistan and all other countries in Central Asia suffer from climate change and the potential role of dust in that climate change needs to be investigated and quantified. Therefore the Central Asian Dust EXperiment (CADEX) conducted first lidar observations in Tajikistan for long-term vertically resolved aerosol measurements with the multiwavelength polarization Raman lidar PollyXT from March 2015–August 2016. A measurement example of a polluted dust layer as well as mean values of intensive optical properties and the aerosol optical thickness measured during the months August 2015 and August 2016 are shown.