From 16-24 April 2010 multiwavelength EARLINET Raman lidar and AERONET Sun photometer measurements
were performed at the Leibniz Institute for Tropospheric Research (IfT) in Leipzig (51.3° N, 12.5° E),
Germany, to monitor the ash layers originating from the eruptions of the Eyjafjallajokull volcano in southern
Iceland. We observed the first ash plumes on 16 April 2010. They showed strong depolarization which indicates
non-spherical particles. Extinction coefficients were as high as 500 Mm-1. We estimate ash mass concentrations
of the order of 1000 μg/m3 in the main plume. For an aged ash plume on 19 April 2010 we observed much
lower extinction coefficients of around 50 Mm-1 which lead to estimated ash mass concentrations of the order
of 100 μg/m3.
EARLINET, the European Aerosol Research Lidar NETwork, established in 2000, is the first coordinated lidar network
for tropospheric aerosol study on the continental scale. The network activity is based on scheduled measurements, a rigorous quality assurance program addressing both instruments and evaluation algorithms, and a standardised data
exchange format. At present, the network includes 27 lidar stations distributed over Europe.
EARLINET performed almost continuous measurements since 15 April 2010 in order to follow the evolution of the
volcanic plume generated from the eruption of the Eyjafjallajökull volcano, providing the 4-dimensional distribution of
the volcanic ash plume over Europe. During the 15-30 April period, volcanic particles were detected over Central Europe
over a wide range of altitudes, from 10 km down to the local planetary boundary layer (PBL). Until 19 April, the
volcanic plume transport toward South Europe was nearly completely blocked by the Alps. After 19 April volcanic
particles were transported to the south and the southeast of Europe. Descending aerosol layers were typically observed
all over Europe and intrusion of particles into the PBL was observed at almost each lidar site that was affected by the
volcanic plume. A second event was observed over Portugal and Spain (6 May) and then over Italy on 9 May 2010. The
volcanic plume was then observed again over Southern Germany on 11 May 2010.
Lidar techniques represent the most suitable tool to obtain information on the aerosol vertical distribution and therefore
to close this kind of observational gap. Lidar networks are fundamental to study aerosol on large spatial scale and to
investigate transport and modification phenomena. These are the motivations why EARLINET, the European Aerosol
Research Lidar Network, was established in 2000. At present, EARLINET consists of 25 lidar stations: 7 single
backscatter lidar stations, 9 Raman lidar stations with the UV Raman channel for independent measurements of aerosol
extinction and backscatter, and 9 multiwavelength Raman lidar stations (elastic channel at 1064 nm, 532 nm, 355 nm,
Raman channels at 532 nm and 355 nm, plus depolarization channel at 532 nm) for the retrieval of aerosol microphysical
properties.
EARLINET data can significantly contribute to the quantification of aerosol concentrations, radiative properties, long-range
transport and budget, and prediction of future trends on European and global scale. It can also contribute to
improve model treatment on a wide range of scales and to a better exploitation of present and future satellite data.
EARLINET is playing an important role in the validation and in the full exploitation of the CALIPSO mission.
EARLINET started correlative measurements for CALIPSO since June 2006. A strategy for correlative measurements
has been defined on the base of the analysis of the high resolution ground track data provided by NASA. Results in terms
of comparisons between EARLINET and available CALIPSO products, both level 1 and level 2 data, are presented.
Coordinated lidar observations of Saharan dust over Europe are performed in the frame of the EARLINET-ASOS
(2006-2011) project, which comprises 25 stations: 16 Raman lidar stations, including 8 multi-wavelength
(3+2 station) Raman lidar stations, are used to retrieve the aerosol microphysical properties. Since
the launch of CALIOP, the two-wavelength lidar on board the CALIPSO satellite (June 2006) our lidar
network has been performing correlative aerosol measurements during CALIPSO overpasses over the
individual stations. In our presentation, we report on the correlative measurements obtained during Saharan
dust intrusions in the period from June 2006 to June 2008. We found that the number of dust events is
generally greatest in late spring, summer and early autumn periods, mainly in southern and south-eastern
Europe. A measurement example is presented that was analyzed to show the potential of a ground based lidar
network to follow a dust event over a specific study area, in correlation with the CALIOP measurements. The
dust transport over the studied area was simulated by the DREAM forecast model. Cross-section analyses of
CALIOP over the study area were used to assess the model performance for describing and forecasting the
vertical and horizontal distribution of the dust field over the Mediterranean. Our preliminary results can be
used to reveal the importance of the synergy between the CALIOP measurement and the dust model, assisted
by ground-based lidars, for clarifying the overall transport of dust over the European continent.
The European Aerosol Research Lidar Network (EARLINET) was established in 2000 to derive a comprehensive, quantitative, and statistically significant data base for the aerosol distribution on the European scale.
At present, EARLINET consists of 25 stations: 16 Raman lidar stations, including 8 multi-wavelength Raman lidar stations which are used to retrieve aerosol microphysical properties.
EARLINET performs a rigorous quality assurance program for instruments and evaluation algorithms. All stations measure simultaneously on a predefined schedule at three dates per week to obtain unbiased data for climatological studies.
Since June 2006 the first backscatter lidar is operational aboard the CALIPSO satellite. EARLINET represents an excellent tool to validate CALIPSO lidar data on a continental scale. Aerosol extinction and lidar ratio measurements provided by the network will be particularly important for that validation.
The measurement strategy of EARLINET is as follows: Measurements are performed at all stations within 80 km from the overpasses and additionally at the lidar station which is closest to the actually overpassed site. If a multi-wavelength Raman lidar station is overpassed then also the next closest 3+2 station performs a measurement.
Altogether we performed more than 1000 correlative observations for CALIPSO between June 2006 and June 2007.
Direct intercomparisons between CALIPSO profiles and attenuated backscatter profiles obtained by EARLINET lidars look very promising.
Two measurement examples are used to discuss the potential of multi-wavelength Raman lidar observations for the validation and optimization of the CALIOP Scene Classification Algorithm.
Correlative observations with multi-wavelength Raman lidars provide also the data base for a harmonization of the CALIPSO aerosol data and the data collected in future ESA lidar-in-space missions.
Multiwavelength Raman lidar observations have matured into a powerful tool for the vertical resolved characterization of optical and microphysical properties of atmospheric aerosol particles. Raman lidars that operate with laser pulses at three wavelengths are the minimum requirement for a comprehensive particle characterization. Parameters that are derived with such systems are particle backscatter and extinction coefficients, and particle extinction-to-backscatter (lidar) ratios. Effective radius and complex refractive index can be derived with inversion algorithms. In the past ten years we carried out regular observations over Leipzig, Germany, with multiwavelength Raman lidar. We could
establish a time series of important aerosol properties. For instance, we find that pollution layers are present in the free troposphere in more than 30% of our observations in each year. These layers result from long-range transport of, e.g., forest-fire smoke from North America and Siberia, anthropogenic pollution from North America, Arctic haze from North polar areas, and mineral dust from the Sahara. Observations were also carried out with our mobile six-wavelength Raman lidar during several international field campaigns since 1997. Those data allow us to establish a first comprehensive overview on the vertical distribution of optical and microphysical particle properties in different areas of the world.
EARLINET-ASOS (European Aerosol Research Lidar Network - Advanced Sustainable Observation System) is a 5-year EC Project started in 2006. Based on the EARLINET infrastructure, it will provide appropriate tools to improve the quality and availability of the continuous observations. The EARLINET multi-year continental scale data set is an excellent instrument to assess the impact of aerosols on the European and global environment and to support future satellite missions. The project is addressed in optimizing instruments and algorithms existing within EARLINET-ASOS, exchanging expertise, with the main goal to build a database with high quality aerosol data. In particular, the optimization of the algorithms for the retrieval of the aerosol optical and microphysical properties is a crucial activity. The main objective is to provide all partners with the possibility to use a common processing chain for the evaluation of their data, from raw signals to final products. Raw signals may come from different types of systems, and final products are profiles of optical properties, like backscatter and extinction, and, if the instrument properties permit, of microphysical properties. This will have a strong impact on the scientific community because data with homogeneous well characterized quality will be made available in nearly real time.
This lecture describes the development of lidar techniques to measure the atmospheric temperature profile. Particular attention is given in the lecture to the technique that uses pure rotational Raman scattering of light by molecular nitrogen and oxygen. At present, this approach to temperature profiling in the atmosphere with lidars has received a new impulse because of recent advances in laser and optoelectronics technologies. The instrumentation aspects that determine the feasibility of one or another lidar technique to measure temperature profiles based on the pure rotational Raman spectrum (PRRS) of N2 and O2 molecules are considered. The primary instrumental problem is isolation of extremely weak Raman-lidar returns within the PRRS of N2 and O2 against the background from the much stronger line of unshifted scattering. Mie + Rayleigh, that simultaneously contributes to lidar returns. Besides, the daytime sky background is the factor that severely hampers daytime lidar measurements especially in the case with Raman lidars. So it is an important task of Raman-lidar technologists to find proper ways to overcome this difficulty that would made it possible the temperature profiling in the atmosphere to be performed whole day round. The approach to achieving this task by use of a Fabry-Perot interferometer (FPI) is discussed in the lecture.
We propose a new optical arrangement of the double grating monochromator (DGRM), intended for use in a pure rotational Raman-lidar. The main idea of the construction proposed is in the use of optical monofibers, to couple two chambers of the DGRM. The coupling with optical monofibers enables isolation of two pairs of spectral portions in the S and O branches of the pure rotational Raman spectra (PRRS) of nitrogen and oxygen symmetric relative to the line of exciting radiation. The use of monofibers provides for optically summing the symmetric portions of the PRRS at the exit of the second monochromator, thus increasing the power of PRRS collected for further temperature retrieval. It is important that this approach provides for better than 107 suppression of the spectral line, due to unshifted Mie+Rayleigh scattering. As calculations and laboratory experiments show the end-to-end transmission of the DGRM, with the account of optical summing mentioned, can compare with the transmission of the interference filters available. At the same time, the DGRM provides better spectral purity of the RRS portions isolated, which is a crucial point of the Raman-lidar temperature measurements. Temperature profiles of the atmosphere acquired with the combined Raman- lidar of the Institute for Tropospheric Research in Leipzig, Germany, equipped with the DGRM proposed, showed a good agreement with the profiles measured with a radiosonge.
The increase of particle surface-area concentration in the stratosphere after strong volcanic eruptions is believed to exacerbate the manmade ozone depletion because of the modified conditions for heterogeneous chemical reactions. To quantify this effect longterm observations of both particle surface-area and ozone concentrations are performed since the eruption of Mt. Pinatubo in June 1991. Surface-area concentrations are measured with a Raman elastic- backscatter lidar at Geeshacht (53.5 degrees N). Ozone measurements are made with ECC sondes by the German Weather Service at Lindenberg (52 degrees N). Surface-area concentrations of the order of 20 micrometers 2cm-3 have been found between 10 and 20 km height during the first two years after the Mt. Pinatubo eruption. In the same height region, ozone losses of more than 20% during winter and spring seasons 1991/92 and 1992/93 have been observed.
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