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 Ångström exponent values (BRAE) (LR: 20–100 sr; BRAE: −0.5 to 3) than northern ones (LR: 30–80 sr; BRAE: −0.5 to 1).
Since its establishment in 2000, EARLINET (European Aerosol Research Lidar NETwork) has provided, through its database, quantitative aerosol properties, such as aerosol backscatter and aerosol ...extinction coefficients, the latter only for stations able to retrieve it independently (from Raman or high-spectral-resolution lidars). These coefficients are stored in terms of vertical profiles, and the EARLINET database also includes the details of the range resolution of the vertical profiles. In fact, the algorithms used in the lidar data analysis often alter the spectral content of the data, mainly acting as low-pass filters to reduce the high-frequency noise. Data filtering is described by the digital signal processing (DSP) theory as a convolution sum: each filtered signal output at a given range is the result of a linear combination of several signal input data samples (relative to different ranges from the lidar receiver), and this could be seen as a loss of range resolution of the output signal. Low-pass filtering always introduces distortions in the lidar profile shape. Thus, both the removal of high frequency, i.e., the removal of details up to a certain spatial extension, and the spatial distortion produce a reduction of the range resolution. This paper discusses the determination of the effective resolution (ERes) of the vertical profiles of aerosol properties retrieved from lidar data. Large attention has been dedicated to providing an assessment of the impact of low-pass filtering on the effective range resolution in the retrieval procedure.
The eruption of the Icelandic volcano Eyjafjallajökull in April–May 2010 represents a "natural experiment" to study the impact of volcanic emissions on a continental scale. For the first time, ...quantitative data about the presence, altitude, and layering of the volcanic cloud, in conjunction with optical information, are available for most parts of Europe derived from the observations by the European Aerosol Research Lidar NETwork (EARLINET). Based on multi-wavelength Raman lidar systems, EARLINET is the only instrument worldwide that is able to provide dense time series of high-quality optical data to be used for aerosol typing and for the retrieval of particle microphysical properties as a function of altitude. In this work we show the four-dimensional (4-D) distribution of the Eyjafjallajökull volcanic cloud in the troposphere over Europe as observed by EARLINET during the entire volcanic event (15 April–26 May 2010). All optical properties directly measured (backscatter, extinction, and particle linear depolarization ratio) are stored in the EARLINET database available at http://www.earlinet.org. A specific relational database providing the volcanic mask over Europe, realized ad hoc for this specific event, has been developed and is available on request at http://www.earlinet.org. During the first days after the eruption, volcanic particles were detected over Central Europe within a wide range of altitudes, from the upper troposphere down to the local planetary boundary layer (PBL). After 19 April 2010, volcanic particles were detected over southern and south-eastern Europe. During the first half of May (5–15 May), material emitted by the Eyjafjallajökull volcano was detected over Spain and Portugal and then over the Mediterranean and the Balkans. The last observations of the event were recorded until 25 May in Central Europe and in the Eastern Mediterranean area. The 4-D distribution of volcanic aerosol layering and optical properties on European scale reported here provides an unprecedented data set for evaluating satellite data and aerosol dispersion models for this kind of volcanic events.
This paper presents a new application of assimilating lidar signals to aerosol forecasting. It aims at investigating the impact of a ground-based lidar network on the analysis and short-term ...forecasts of aerosols through a case study in the Mediterranean basin. To do so, we employ a data assimilation (DA) algorithm based on the optimal interpolation method developed in the Polair3D chemistry transport model (CTM) of the Polyphemus air quality modelling platform. We assimilate hourly averaged normalised range-corrected lidar signals (PR2) retrieved from a 72 h period of intensive and continuous measurements performed in July 2012 by ground-based lidar systems of the European Aerosol Research Lidar Network (EARLINET) integrated into the Aerosols, Clouds, and Trace gases Research InfraStructure (ACTRIS) network and an additional system in Corsica deployed in the framework of the pre-ChArMEx (Chemistry-Aerosol Mediterranean Experiment)/TRAQA (TRAnsport a longue distance et Qualite de l'Air) campaign. This lidar campaign was dedicated to demonstrating the potential operationality of a research network like EARLINET and the potential usefulness of assimilation of lidar signals to aerosol forecasts. Particles with an aerodynamic diameter lower than 2.5 mu m (PM2.5) and those with an aerodynamic diameter higher than 2.5 mu m but lower than 10 mu m (PM10-2.5) are analysed separately using the lidar observations at each DA step. First, we study the spatial and temporal influences of the assimilation of lidar signals on aerosol forecasting. We conduct sensitivity studies on algorithmic parameters, e.g. the horizontal correlation length (Lh) used in the background error covariance matrix (50 km, 100 km or 200 km), the altitudes at which DA is performed (0.75-3.5 km, 1.0-3.5 km or 1.5-3.5 km a.g.l.) and the assimilation period length (12 h or 24 h). We find that DA with Lh = 100 km and assimilation from 1.0 to 3.5 km a.g.l. during a 12 h assimilation period length leads to the best scores for PM10 and PM2.5 during the forecast period with reference to available measurements from surface networks. Secondly, the aerosol simulation results without and with lidar DA using the optimal parameters (Lh = 100 km, an assimilation altitude range from 1.0 to 3.5 km a.g.l. and a 12 h DA period) are evaluated using the level 2.0 (cloud-screened and quality-assured) aerosol optical depth (AOD) data from AERONET, and mass concentration measurements (PM10 or PM2.5) from the French air quality (BDQA) network and the EMEP-Spain/Portugal network. The results show that the simulation with DA leads to better scores than the one without DA for PM2.5, PM10and AOD. Additionally, the comparison of model results to evaluation data indicates that the temporal impact of assimilating lidar signals is longer than 36 h after the assimilation period.
Global climatological distributions of key aerosol quantities (extinction, optical depth, mass, and surface area density) are shown in comparison with results from a three-dimensional global model ...including stratospheric and tropospheric aerosol components. Large increases of anthropogenic sulfur production at tropical latitudes by developing countries may explain these rather large predicted changes of stratospheric sulfate.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A measurement of the absolute fluorescence yield of the 337 nm nitrogen band, relevant to ultra-high energy cosmic ray (UHECR) detectors, is reported. Two independent calibrations of the fluorescence ...emission induced by a 120 GeV proton beam were employed: Cherenkov light from the beam particle and calibrated light from a nitrogen laser. The fluorescence yield in air at a pressure of 1013 hPa and temperature of 293 K was found to be Y 337 = 5.61 +/- 0.06 stat +/- 0.22 syst photons/MeV. When compared to the fluorescence yield currently used by UHECR experiments, this measurement improves the uncertainty by a factor of three, and has a significant impact on the determination of the energy scale of the cosmic ray spectrum.
Lidar measurements were performed in the framework of the EARLINET project during the last eruptions (July–August 2001 and November 2002) of the Etna volcano. Both aerosol backscattering and ...extinction coefficients show the presence of remarkable aerosol layers in central and especially in southern Europe during the Etna eruptions periods. The aerosol layer altitudes ranged from 1 to 6
km. Back-trajectory, lidar ratio and backscatter related Angstrom coefficient analyses show that most of the aerosol layers originated from the Etna eruption and were made of sulfates and small absorbing volcanic ash. Thanks to the EARLINET network, the space and temporal distributions of volcanic aerosol have been studied over continental scale.
This paper introduces the Atmospheric Measurement Techniques special issue on tropospheric profiling, which was conceived to host full papers presenting the results shown at the 9th International ...Symposium on Tropospheric Profiling (ISTP9). ISTP9 was held in L'Aquila (Italy) from 3 to 7 September 2012, bringing together 150 scientists representing of 28 countries and 3 continents. The tropospheric profiling special issue collects the highlights of ISTP9, reporting recent advances and future challenges in research and technology development.
Aerosol transport simulations within Europe were performed with the regional transport model COSMO-MUSCAT for two different time periods, July 19–26, 2006 and February 16–26, 2007. Simulated
PM
2.5, ...backscatter profiles and aerosol optical depths (AODs) were compared to observations, showing good agreements in magnitude, shape and day-to-day variations. Maximum AODs (>0.4) were found over Middle Europe and minimum AODs (<0.13) over the ocean during both time periods, corresponding to regions of high (
PM
2.5 > 10 μg m
−3) and low (
PM
2.5 < 4.0 μg m
−3) concentration near the surface. Vertical aerosol distributions were evaluated with lidar measurements from the EARLINET ground network and CALIPSO satellite retrievals. The characteristic vertical distribution and the differences for the summer and the winter cases were represented well by the regional model. Mean differences between −5.0 × 10
−7 to−2.0 × 10
−7 m
−1 sr
−1 (summer case) and −2.3 × 10
−6 to 1.0 × 10
−6 m
−1 sr
−1 (winter case) from 0.0 to 2.5 km altitude were found between observed (space-based lidar) and simulated backscatter coefficients. For the cases that were investigated in this study different prescriptions of the vertical distribution at the lateral model boundaries resulted in only small differences in aerosol distributions within the interior of the model region.
► Simulation of European aerosol for two different time periods. ► Evaluation with observed PM2.5, AOD and backscatter coefficients. ► Lidar profiles were used at the lateral model boundaries. ► Observed AOD values were used to adjust the vertical distributions. ► Usage of a regional transport model.
Water vapour (H2O) is one of the operationallyretrieved key species of the Michelson Interferometer forPassive Atmospheric Sounding (MIPAS) instrument aboardthe Environmental Satellite (ENVISAT) ...which was launchedinto its sun-synchronous orbit on 1 March 2002 and operateduntil April 2012. Within the MIPAS validation activities,independent observations from balloons, aircraft, satellites,and ground-based stations have been compared to EuropeanSpace Agency (ESA) version 4.61 operational H2Odata comprising the time period from July 2002 until March2004 where MIPAS measured with full spectral resolution.No significant bias in the MIPAS H2O data is seen in thelower stratosphere (above the hygropause) between about15 and 30 km. Differences of H2O quantities observed byMIPAS and the validation instruments are mostly well withinthe combined total errors in this altitude region. In the upperstratosphere (above about 30 km), a tendency towardsa small positive bias (up to about 10 %) is present in theMIPAS data when compared to its balloon-borne counterpartMIPAS-B, to the satellite instruments HALOE (HalogenOccultation Experiment) and ACE-FTS (AtmosphericChemistry Experiment, Fourier Transform Spectrometer),and to the millimeter-wave airborne sensor AMSOS (AirborneMicrowave Stratospheric Observing System). In themesosphere the situation is unclear due to the occurrenceof different biases when comparing HALOE and ACE-FTSdata. Pronounced deviations between MIPAS and the correlativeinstruments occur in the lowermost stratosphere and upper troposphere, a region where retrievals of H2O are mostchallenging. Altogether it can be concluded that MIPAS H2Oprofiles yield valuable information on the vertical distributionof H2O in the stratosphere with an overall accuracy ofabout 10 to 30% and a precision of typically 5 to 15% –well within the predicted error budget, showing that theseglobal and continuous data are very valuable for scientificstudies. However, in the region around the tropopause retrievedMIPAS H2O profiles are less reliable, suffering froma number of obstacles such as retrieval boundary and cloudeffects, sharp vertical discontinuities, and frequent horizontalgradients in both temperature and H2O volume mixing ratio(VMR). Some profiles are characterized by retrieval instabilities.
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