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Mechanisms behind the phenomenon of Arctic amplification are widely discussed. To contribute to this debate, the (AC)3 project was established in 2016 (www.ac3-tr.de/). It comprises modeling and data analysis efforts as well as observational elements. The project has assembled a wealth of ground-based, airborne, shipborne, and satellite data of physical, chemical, and meteorological properties of the Arctic atmosphere, cryosphere, and upper ocean that are available for the Arctic climate research community. Short-term changes and indications of long-term trends in Arctic climate parameters have been detected using existing and new data. For example, a distinct atmospheric moistening, an increase of regional storm activities, an amplified winter warming in the Svalbard and North Pole regions, and a decrease of sea ice thickness in the Fram Strait and of snow depth on sea ice have been identified. A positive trend of tropospheric bromine monoxide (BrO) column densities during polar spring was verified. Local marine/biogenic sources for cloud condensation nuclei and ice nucleating particles were found. Atmospheric–ocean and radiative transfer models were advanced by applying new parameterizations of surface albedo, cloud droplet activation, convective plumes and related processes over leads, and turbulent transfer coefficients for stable surface layers. Four modes of the surface radiative energy budget were explored and reproduced by simulations. To advance the future synthesis of the results, cross-cutting activities are being developed aiming to answer key questions in four focus areas: lapse rate feedback, surface processes, Arctic mixed-phase clouds, and airmass transport and transformation. more...

SRef-ID: 1607-7962/gra/EGU05-A-08329. Geophys. Res. Abstracts

[1] During the Lindenberg Aerosol Characterization Experiment (LACE 98) simultaneous measurements with ground-based and airborne lidars and with two aircraft equipped with aerosol in situ instrumentation were performed. From the lidar measurements, particle backscatter coefficients at up to eight wavelengths between 320 and 1064 nm and particle extinction coefficients at 2-3 wavelengths between 292 and 532 nm were determined. Thus, for the first time, an extensive set of optical particle properties from several lidar platforms was available for the inversion into particle microphysical quantities. For this purpose, two different inversion algorithms were used, which provide particle effective radius, volume, surface-area, and number concentrations, and complex refractive index. The single-scattering albedo follows from Mie-scattering calculations. The parameters were compared to the ones from airborne measurements of particle size distributions and absorption coefficients. Two measurement cases were selected. During the night of 9-10 August 1998 measurements were taken in a biomass-burning aerosol layer in the free troposphere, which was characterized by a particle optical depth of about 0.1 at 550 nm. Excellent agreement between remote-sensing and in situ measurements was found. In the center of this plume the effective radius was approximately 0.25 mum, and all methods showed rather high complex refractive indices, ranging from 1.56-1.66 in real part and from 0.05- 0.07i in imaginary part. The single-scattering albedo showed low values from 0.78-0.83 at 532 nm. The second case, taken on 11 August 1998, presents the typical conditions of a polluted boundary layer in central Europe. Optical depth was 0.35 at 550 nm, and particle effective radii were 0.1-0.2 mum. In contrast to the first case, imaginary parts of the refractive index were below 0.03i. Accordingly, the single-scattering albedo ranged from 0.87-0.95. more...

EARLINET (European Aerosol Research Lidar Network to Establish an Aerosol Climatology) is a joint project of 19 lidar groups operating aerosol lidar systems at 21 stations over a large part of Europe, plus one group focussing on mathematical problems associated with the retrieval of aerosol properties from lidar observations. The main goal of EARLINET is to establish a comprehensive statistically representative data set of the aerosol vertical distribution. For this purpose, each lidar group performs vertical aerosol soundings on a routine basis three times a week on preselected days and times. Additionally several special measurements (e.g. on Saharan dust, temporal cycles, rural and urban differences, long and medium range transport) are part of the project. more...

The German Aerosol Lidar Network has attempted, for the first time worldwide, to establish a cli- matological data set for the aerosol vertical distribution over several stations in a quantitative and coordinated approach. Quantitative results have been obtained by employing advanced lidar methods like Raman or scanning lidar to retrieve profiles of the extinction coefficient directly. To provide for a sufficiently homogeneous data set substantial effort was put into data quality assurance. Intercom- parisons were performed at both system and retrieval algorithm levels. A very satisfactory agreement between the different systems was achieved. A rather large data set of aerosol extinction and backscat- ter profiles was collected using regularly scheduled measurements on predetermined days and times to avoid a bias due to ”preferred” weather conditions for lidar observations. A large number of ad- ditional measurements were devoted to studies of special weather conditions. The results of special studies related to the aerosol distribution associated with high pressure systems and cold front pas- sages are reported as well as special studies on the long term development of the stratospheric aerosol distribution, transport processes in an Alpine valley, and long range transport of aerosol. The retrieval of aerosol microphysical properties using lidar measurements at several wavelengths is described mathematically and applied to actual examples, showing very promising results. Several methods for the statistical analysis of the climatological data set are developed making use of the simultaneously collected data set of backtrajectories. Products of these analyses include the seasonal dependence of boundary layer heights, the mean extinction and backscatter profiles, the mean optical depth, sep- arately for PBL and free troposphere, the seasonal dependence of aerosol extinction, the statistical distribution of aerosol extinction and of extinction-to-backscatter ratio values, and the dependence of aerosol optical properties on the airmass history. more...

The present knowledge of the aerosol distribution is not sufficient to estimate the aerosol influence on global and regional environmental conditions and climate. This observational gap can be closed by using advanced laser remote sensing. EARLINET (European Aerosol Research Lidar Network) is the first aerosol lidar network, established in 2000, with the main goal to provide a comprehensive, quantitative, and statistically significant database for the aerosol distribution on a continental scale. EARLINET is a coordinated network of European stations (25 at present) using advanced lidar methods for the vertical profiling of aerosols. The network activity is based on simultaneous scheduled measurements, a rigorous quality assurance program addressing both instruments and evaluation algorithms, and a standardised data exchange format. Further observations are performed to monitor special events. EARLINET-ASOS (Advanced Sustainable Observation System) is a five year EC Project started in 2006, based on the EARLINET infrastructure. The main objectives are: to make EARLINET a world-leading instrument for the observation of the 4-D aerosol distribution on continental scale; to foster aerosol-related process studies, validation of satellite sensors, model development and validation, assimilation of aerosol data into operational models; and to build a comprehensive climatology of the aerosol distribution. more...

EARLINET, the European Aerosol Research Lidar Network, is the first aerosol lidar network, established in 2000, with the main goal to provide a comprehensive, quantitative, and statistically significant data base for the aerosol distribution on a continental scale. At present, 23 stations distributed over Europe are part of the network. The EARLINET-ASOS (Advanced Sustainable Observation System) EC Project, starting on the EARLINET infrastructure, will contribute to the improvement of continuing observations and methodological developments that are urgently needed to provide the multi-year continental scale data set necessary to assess the impact of aerosols on the European and global environment and to support future satellite missions. The main objective of EARLINET-ASOS 5-year project, started on 1 March 2006, is to improve the EARLINET infrastructure resulting in a better spatial and temporal coverage of the observations, continuous quality control for the complete observation system, and fast availability of standardized data products. This will be reached by defining and using common standards for instruments, operation procedures, observation schemes, data processing including advanced retrieval algorithms, and dissemination of data. The expected outcome is the most comprehensive data source for the 4-D spatio-temporal distribution of aerosols on a continental scale. more...