Showing papers by "Gelsomina Pappalardo published in 2010"

EARLINET correlative measurements for CALIPSO: First intercomparison results

Abstract: [1] A strategy for European Aerosol Research Lidar Network (EARLINET) correlative measurements for Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) has been developed. These EARLINET correlative measurements started in June 2006 and are still in progress. Up to now, more than 4500 correlative files are available in the EARLINET database. Independent extinction and backscatter measurements carried out at high-performance EARLINET stations have been used for a quantitative comparison with CALIPSO level 1 data. Results demonstrate the good performance of CALIPSO and the absence of evident biases in the CALIPSO raw signals. The agreement is also good for the distribution of the differences for the attenuated backscatter at 532 nm ((CALIPSO-EARLINET)/EARLINET (%)), calculated in the 1–10 km altitude range, with a mean relative difference of 4.6%, a standard deviation of 50%, and a median value of 0.6%. A major Saharan dust outbreak lasting from 26 to 31 May 2008 has been used as a case study for showing first results in terms of comparison with CALIPSO level 2 data. A statistical analysis of dust properties, in terms of intensive optical properties (lidar ratios, Angstrom exponents, and color ratios), has been performed for this observational period. We obtained typical lidar ratios of the dust event of 49 ± 10 sr and 56 ± 7 sr at 355 and 532 nm, respectively. The extinction-related and backscatter-related Angstrom exponents were on the order of 0.15–0.17, which corresponds to respective color ratios of 0.91–0.95. This dust event has been used to show the methodology used for the investigation of spatial and temporal representativeness of measurements with polar-orbiting satellites.

Observation of non-spherical ultragiant aerosol using a microwave radar

Abstract: [1] Observations of ultragiant aerosol particles performed at the CNR-IMAA Atmospheric Observatory using a Ka-Band Doppler radar in four different periods from 19 April to 13 May 2010 are presented. In the reported cases, the aerosol radar signatures are characterized by a similar scenario. In particular, the linear depolarization ratio shows values higher than −4 dB probably related to the effect of bulk density and to the non-sphericity of the ultragiant particles. During the same period, volcanic aerosol layers coming from Eyjafjallajokull volcano were observed over most of European countries, including Southern Italy, using lidar technique. The observation of volcanic layers over Potenza by multi-wavelength Raman lidar measurements suggests a volcanic origin of the ultragiant aerosol particles observed by the radar, revealing that these particles might travel in the atmosphere for more than 4000 km after their injection in the atmosphere.

Dispersion and evolution of the Eyjafjallajökull ash plume over Europe: vertically resolved measurements with the European LIDAR network EARLINET

Abstract: EARLINET, the European Aerosol Research Lidar NETwork, established in 2000 is the first coordinated lidar network for tropospheric aerosol study on 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 26 lidar stations distributed over Europe. EARLINET has been closely monitoring the cloud of volcanic ash from the Eyjafjallajoekull volcano in Iceland since it started erupting on 15 April. EARLINET is providing data about the presence, altitude and layering of the plume, together with optical information all over Europe. Updated measurement reports and more information about EARLINET can be found at www.earlinet.org.

EARLINET observations of the Eyjafjallajökull ash plume over Europe

Abstract: 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 EyjafjallajAƒÂ¶kull 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.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Long-term aerosol and cloud database from correlative EARLINET-CALIPSO observations

Abstract: The European Aerosol Research Lidar Network, EARLINET, performs correlative observations during CALIPSO overpasses based on a sophisticated measurement strategy since June 2006. Within a dedicated activity supported by the European Space Agency (ESA), sixteen EARLINET stations contributed about 1500 measurements during an intensive observational period from May 2008 to October 2009. From these measurements, we establish a long-term aerosol and cloud database of correlative EARLINET-CALIPSO observations. This database shall provide a basis for homogenizing long-term space-borne observations conducted with different lidar instruments operating at different wavelengths on various platforms over the next decade(s). The database is also used to study the quality and representativeness of satellite lidar cross sections along an orbit against long-term lidar network observations on a continental scale.

Representativeness of aerosol measurements: EARLINET-CALIPSO correlative study

Abstract: The high variability of tropospheric aerosols, both in space and time, is the main cause of the high uncertainty about radiative forcing related to tropospheric aerosols and their interaction with clouds. Because of the lack of high resolution aerosol global vertical profiles, the vertical mixing has not been considered so far in studies of spatial and temporal variability. The CALIPSO mission provides the first opportunity to investigate the 4-D aerosol and cloud fields in detail. However, because of the CALIOP small footprint and the revisit time of 16 days, correlative ground-based lidar observations are necessary in order to investigate the representativeness of these satellite observations. EARLINET, the European Aerosol Research Lidar Network, started correlative measurements for CALIPSO in June 2006, right after the CALIPSO launch. An integrated study of CALIPSO and EARLINET correlative measurements opens new possibilities for spatial (both horizontal and vertical) and temporal representativeness investigation of polar-orbit satellite measurements also in terms of revisit time.

EARLINET revealed four-dimensional distribution of volcanic ash

Abstract: Aerosols originating from volcanic emissions influence the climate and environment, and they could be dangerous to aircraft in flight. For this reason, the airspace over Europe was closed for several days during the latest eruption of Eyjafjallajökull volcano in April–May 2010. Eyjafjallajökull is one of the smallest volcanoes in Iceland. An explosive eruption began around midnight on 14 April, and a volcanic plume was observed early in the morning of the same day. Eruptive activity continued almost without interruption until 24 May. Near the volcano, the resulting plume reached a variable maximum height (between 2 and 9km above sea level) during this period, which lasted for more than one month. Depending on the wind direction, the plume was transported toward different regions of continental Europe and the Atlantic Ocean at different altitudes. Light detection and ranging (lidar) techniques represent an optimal tool for obtaining range-resolved data on volcanic ash plumes.1–3 EARLINET, the European Aerosol Research Lidar NETwork, established in 2000, is the first coordinated lidar network for tropospheric aerosol studies on a continental scale.4 Network activity consists of scheduled measurements, a rigorous quality assurance program addressing both the instruments and the evaluation algorithms, and a standard data exchange format.5–7 The network currently includes 27 lidar stations distributed over Europe as shown in Figure 1. Soon after the explosive eruption of the Eyjafjallajökull volcano began, an alert was distributed to all EARLINET stations informing them about a large amount of ash directed toward northwestern Europe. Almost all of the stations made measurements whenever weather conditions permitted during the Figure 1. Map of lidar stations within EARLINET.

Water vapour profiling in cloudy conditions integrating Raman lidar and passive microwave observations

Abstract: At the Istituto di Metodologie per l'Analisi Ambientale of the Italian National Research Council (CNR-IMAA) an advanced observatory for the ground-based remote sensing of the atmosphere is operative. This facility is equipped with several instruments including two multi-wavelength Raman lidars, one of which mobile, a microwave profiler, a 36 GHz Doppler polarimetric radar, two laser ceilometers, a sun photometer, a surface radiation station and three radiosounding stations. CNR-IMAA atmospheric observatory (CIAO) is located in Southern Italy on the Apennine mountains (40.60N, 15.72E, 760 m a.s.l.), less than 150 km from the West, South and East coasts. The site is in a valley surrounded by low mountains (<1100 m a.s.l.) and this location offers an optimal opportunity to study different kinds of weather and climate regimes. CIAO represents an optimal site where testing possible synergies between active and passive techniques for improving the profiling capabilities of several atmospheric key variables, such as aerosol, water vapour and clouds, and for the development of an integration strategy for their long-term monitoring. CIAO strategy aims at the combination of observations provided by active and passive sensors for providing advanced retrievals of atmospheric parameters exploiting both the high vertical resolution of active techniques and the typical operational capabilities of passive sensors. This combination offers a high potential for profiling atmospheric parameters in an enlarged vertical range nearly independently on the atmospheric conditions. In this work, we describe two different integration approaches for the improvement of water vapour profiling during cloudy condition through the combination of Raman lidar and microwave profiler measurements. These approaches are based on the use of Kalman filtering and Tikhonov regularization methods for the solution of the radiative transfer equation in the microwave region. The accuracy of the retrieved water vapour profiles during cloudy conditions is improved by the use of the water vapour Raman lidar profiles, retrieved up to a maximum height level located around the cloud base region (depending on their optical thickness), as a constraint to the obtained solution set. The presented integration approaches allow us to provide physically consistent solution to the inverse problem in the microwave region retrieving water vapour vertical profiles also in presence of thick clouds. The integration of Raman lidar and microwave measurements also provides a continuous high-resolution estimation of the water vapour content in the full troposphere and, therefore, a useful tool for the evaluation of model capability to capture mean aspects of the water vapour field in nearly all weather conditions as well as for the identification of possible discrepancies between observations and models.