scholarly journals Optical properties of long-range transported Saharan dust over Barbados as measured by dual-wavelength depolarization Raman lidar measurements

2015 ◽  
Vol 15 (19) ◽  
pp. 11067-11080 ◽  
Author(s):  
S. Groß ◽  
V. Freudenthaler ◽  
K. Schepanski ◽  
C. Toledano ◽  
A. Schäfler ◽  
...  
Keyword(s):  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Long Range ◽  
Optical Depth ◽  
Layer Structure ◽  
Dual Wavelength ◽  
Saharan Dust ◽  
Dust Layer ◽  
Mean Values ◽  
532 Nm

Abstract. Dual-wavelength Raman and depolarization lidar observations were performed during the Saharan Aerosol Long-range Transport and Aerosol-Cloud interaction Experiment in Barbados in June and July 2013 to characterize the optical properties and vertical distribution of long-range transported Saharan dust after transport across the Atlantic Ocean. Four major dust events were studied during the measurements from 15 June to 13 July 2013 with aerosol optical depths at 532 nm of up to 0.6. The vertical aerosol distribution was characterized by a three-layer structure consisting of the boundary layer, the entrainment or mixing layer and the pure Saharan dust layer. The upper boundary of the pure dust layer reached up to 4.5 km in height. The contribution of the pure dust layer was about half of the total aerosol optical depth at 532 nm. The total dust contribution was about 50–70 % of the total aerosol optical depth at 532 nm. The lidar ratio within the pure dust layer was found to be wavelength independent with mean values of 53 ± 5 sr at 355 nm and 56 ± 7 sr at 532 nm. For the particle linear depolarization ratio, wavelength-independent mean values of 0.26 ± 0.03 at 355 nm and 0.27 ± 0.01 at 532 nm have been found.

scholarly journals Characterization of long-range transported Saharan dust at the Caribbean by dual-wavelength depolarization Raman lidar measurements

2015 ◽  
Vol 15 (13) ◽  
pp. 19325-19366 ◽  
Author(s):  
S. Groß ◽  
V. Freudenthaler ◽  
K. Schepanski ◽  
C. Toledano ◽  
A. Schäfler ◽  
...  
Keyword(s):  
Long Range ◽  
Layer Structure ◽  
Mixing Layer ◽  
Dual Wavelength ◽  
Saharan Dust ◽  
Dust Layer ◽  
Mean Values ◽  
Linear Depolarization Ratio ◽  
Dust Events ◽  
532 Nm

Abstract. Dual-wavelength Raman and depolarization lidar observations were performed during the SALTRACE campaign at Barbados in June and July 2013 to characterize the optical properties and vertical distribution of long-range transported Saharan dust at the end of its way across the Atlantic Ocean. Four major dust events were studied during the measurements from 15 June to 13 July 2013 with aerosol optical depths of up to 0.6. The vertical aerosol distribution was characterized by a three-layer structure consisting of the boundary layer, the entrainment or mixing layer, and the pure Saharan dust layer. The upper boundary of the pure dust layer reached up to 4.5 km height. The contribution of the pure dust layer was about half of the total AOD. The total dust contribution was about 50–70 % of the total AOD. The lidar ratio within the pure dust layer was found to be wavelength independent with mean values of 53 ± 5 sr at 355 nm and 56 ± 7 sr at 532 nm. For the particle linear depolarization ratio wavelength independent mean values of 0.26 ± 0.03 at 355 nm and 0.27 ± 0.01 at 532 nm have been found.

scholarly journals Using the OMI Aerosol Index and Absorption Aerosol Optical Depth to evaluate the NASA MERRA Aerosol Reanalysis

2014 ◽  
Vol 14 (23) ◽  
pp. 32177-32231 ◽  
Author(s):  
V. Buchard ◽  
A. M. da Silva ◽  
P. R. Colarco ◽  
A. Darmenov ◽  
C. A. Randles ◽  
...  
Keyword(s):  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Biomass Burning ◽  
Saharan Dust ◽  
Aerosol Layer ◽  
Anthropogenic Aerosols ◽  
Aerosol Absorption ◽  
Modis Aod ◽  
Aerosol Index

Abstract. A radiative transfer interface has been developed to simulate the UV Aerosol Index (AI) from the NASA Goddard Earth Observing System version 5 (GEOS-5) aerosol assimilated fields. The purpose of this work is to use the AI and Aerosol Absorption Optical Depth (AAOD) derived from the Ozone Monitoring Instrument (OMI) measurements as independent validation for the Modern Era Retrospective analysis for Research and Applications Aerosol Reanalysis (MERRAero). MERRAero is based on a version of the GEOS-5 model that is radiatively coupled to the Goddard Chemistry, Aerosol, Radiation, and Transport (GOCART) aerosol module and includes assimilation of Aerosol Optical Depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. Since AI is dependent on aerosol concentration, optical properties and altitude of the aerosol layer, we make use of complementary observations to fully diagnose the model, including AOD from the Multi-angle Imaging SpectroRadiometer (MISR), aerosol retrievals from the Aerosol Robotic Network (AERONET) and attenuated backscatter coefficients from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission to ascertain potential misplacement of plume height by the model. By sampling dust, biomass burning and pollution events in 2007 we have compared model produced AI and AAOD with the corresponding OMI products, identifying regions where the model representation of absorbing aerosols was deficient. As a result of this study over the Saharan dust region, we have obtained a new set of dust aerosol optical properties that retains consistency with the MODIS AOD data that were assimilated, while resulting in better agreement with aerosol absorption measurements from OMI. The analysis conducted over the South African and South American biomass burning regions indicates that revising the spectrally-dependent aerosol absorption properties in the near-UV region improves the modeled-observed AI comparisons. Finally, during a period where the Asian region was mainly dominated by anthropogenic aerosols, we have performed a qualitative analysis in which the specification of anthropogenic emissions in GEOS-5 is adjusted to provide insight into discrepancies observed in AI comparisons.

scholarly journals Lidar Measuremnt on Dust Transport from the Saharan Desert to the Iran Plateau

2020 ◽  
Vol 237 ◽  
pp. 02020
Author(s):  
Hossein Panahifar ◽  
Ruhollah Moradhaseli ◽  
Hadi Bourzoie ◽  
Mahdi Gholami ◽  
Hamid Reza Khalesifard
Keyword(s):  
Trajectory Analysis ◽  
Saharan Dust ◽  
Dust Particles ◽  
Raman Lidar ◽  
Dust Layer ◽  
Mean Values ◽  
Dust Transport ◽  
Lidar Ratio ◽  
532 Nm ◽  
Iran Plateau

Optical properties of long-range Saharan dust particles transported to the Iran Plateau have been investigated. The results were derived from the measurements of a dual-wavelength Depolarized backscatter/Raman lidar and a Cimel CE318-2 sunphotometer. Observations were performed in Zanjan, Northwest Iran. The backward trajectory analysis show that the lofted dust plumes come from the Saharan desert and travel along Mediterranean Sea and Turkey toward Iran. The lidar ratio within the lofted dust layer has been found with mean values of 50 sr at 532 nm. For the depolarization ratio, mean values of 25% have been found.

scholarly journals Using the OMI aerosol index and absorption aerosol optical depth to evaluate the NASA MERRA Aerosol Reanalysis

2015 ◽  
Vol 15 (10) ◽  
pp. 5743-5760 ◽  
Author(s):  
V. Buchard ◽  
A. M. da Silva ◽  
P. R. Colarco ◽  
A. Darmenov ◽  
C. A. Randles ◽  
...  
Keyword(s):  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Biomass Burning ◽  
Saharan Dust ◽  
Aerosol Layer ◽  
Anthropogenic Aerosols ◽  
Aerosol Absorption ◽  
Modis Aod ◽  
Aerosol Index

Abstract. A radiative transfer interface has been developed to simulate the UV aerosol index (AI) from the NASA Goddard Earth Observing System version 5 (GEOS-5) aerosol assimilated fields. The purpose of this work is to use the AI and aerosol absorption optical depth (AAOD) derived from the Ozone Monitoring Instrument (OMI) measurements as independent validation for the Modern Era Retrospective analysis for Research and Applications Aerosol Reanalysis (MERRAero). MERRAero is based on a version of the GEOS-5 model that is radiatively coupled to the Goddard Chemistry, Aerosol, Radiation, and Transport (GOCART) aerosol module and includes assimilation of aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. Since AI is dependent on aerosol concentration, optical properties and altitude of the aerosol layer, we make use of complementary observations to fully diagnose the model, including AOD from the Multi-angle Imaging SpectroRadiometer (MISR), aerosol retrievals from the AErosol RObotic NETwork (AERONET) and attenuated backscatter coefficients from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission to ascertain potential misplacement of plume height by the model. By sampling dust, biomass burning and pollution events in 2007 we have compared model-produced AI and AAOD with the corresponding OMI products, identifying regions where the model representation of absorbing aerosols was deficient. As a result of this study over the Saharan dust region, we have obtained a new set of dust aerosol optical properties that retains consistency with the MODIS AOD data that were assimilated, while resulting in better agreement with aerosol absorption measurements from OMI. The analysis conducted over the southern African and South American biomass burning regions indicates that revising the spectrally dependent aerosol absorption properties in the near-UV region improves the modeled-observed AI comparisons. Finally, during a period where the Asian region was mainly dominated by anthropogenic aerosols, we have performed a qualitative analysis in which the specification of anthropogenic emissions in GEOS-5 is adjusted to provide insight into discrepancies observed in AI comparisons.

scholarly journals Saharan dust contribution to the Caribbean summertime boundary layer – a lidar study during SALTRACE

2016 ◽  
Vol 16 (18) ◽  
pp. 11535-11546 ◽  
Author(s):  
Silke Groß ◽  
Josef Gasteiger ◽  
Volker Freudenthaler ◽  
Thomas Müller ◽  
Daniel Sauer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Marine Boundary Layer ◽  
Volume Fraction ◽  
Saharan Dust ◽  
Depolarization Ratio ◽  
Mean Values ◽  
Lidar Ratio ◽  
Linear Depolarization Ratio

Abstract. Dual-wavelength lidar measurements with the small lidar system POLIS of the Ludwig-Maximilians-Universität München were performed during the SALTRACE experiment at Barbados in June and July 2013. Based on high-accuracy measurements of the linear depolarization ratio down to about 200 m above ground level, the dust volume fraction and the dust mass concentration within the convective marine boundary layer can be derived. Additional information from radiosonde launches at the ground-based measurement site provide independent information on the convective marine boundary layer height and the meteorological situation within the convective marine boundary layer. We investigate the lidar-derived optical properties, the lidar ratio and the particle linear depolarization ratio at 355 and 532 nm and find mean values of 0.04 (SD 0.03) and 0.05 (SD 0.04) at 355 and 532 nm, respectively, for the particle linear depolarization ratio, and (26 ± 5) sr for the lidar ratio at 355 and 532 nm. For the concentration of dust in the convective marine boundary layer we find that most values were between 20 and 50 µgm−3. On most days the dust contribution to total aerosol volume was about 30–40 %. Comparing the dust contribution to the column-integrated sun-photometer measurements we see a correlation between high dust contribution, high total aerosol optical depth and a low Angström exponent, and of low dust contribution with low total aerosol optical depth.

scholarly journals The potential of elastic/polarization lidars to retrieve extinction profiles

2019 ◽  
Author(s):  
Elina Giannakaki ◽  
Panos Kokkalis ◽  
Eleni Marinou ◽  
Nikolaos S. Bartsotas ◽  
Vassilis Amiridis ◽  
...  
Keyword(s):  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Dust Particles ◽  
Depolarization Ratio ◽  
Dust Component ◽  
Lidar Ratio ◽  
Linear Depolarization Ratio ◽  
Aerosol Types ◽  
532 Nm

Abstract. In this study we estimate the particle extinction profiles at Finokalia, Crete, using only the information provided by the elastic and polarization channels of a PollyXT lidar system. Most of the time Finokalia site is affected by only two aerosol types, i.e. marine and dust particles. These two aerosol types, having different optical properties, permit the separation of aerosol mixture. The proposed method uses the particle backscatter profiles at 532 nm and the vertically resolved particle linear depolarization ratio measurements at the same wavelength. The particle linear depolarization ratio and the lidar ratio values of pure aerosol types are taken from literature. The total extinction profile is then estimated and compared well with Raman retrievals. Any difference between the proposed methodology and Raman extinction profiles indicates that the non-dust component could be probably attributed to polluted marine or polluted continental aerosols. Comparison with sun-photometric aerosol optical depth observations is performed as well during daytime with reasonable differences between the two instruments. Differences in the total aerosol optical depth is attributed to the limited ability of the lidar to correctly represent the aerosol optical properties in the near range due to overlap problem.

scholarly journals February 2017 extreme Saharan dust outbreak in the Iberian Peninsula: from lidar-derived optical properties to evaluation of forecast models

2018 ◽  
Author(s):  
Alfonso J. Fernández ◽  
Michaël Sicard ◽  
Maria J. Costa ◽  
Juan L. Guerrero-Rascado ◽  
José L. Gómez-Amo ◽  
...  
Keyword(s):  
Optical Properties ◽  
Iberian Peninsula ◽  
Saharan Dust ◽  
Aerosol Optical Properties ◽  
Dust Layer ◽  
Dust Transport ◽  
Forecast Models ◽  
Winter Time ◽  
532 Nm ◽  
Limited Height

Abstract. An unprecedented extreme Saharan dust event was registered in winter time from 20 to 23 February 2017 over the Iberian Peninsula (IP). We report on aerosol optical properties observed under this extreme dust outbreak through remote sensing (active and passive) techniques. For that, EARLINET (European Aerosol Research LIdar NETwork) lidar and AERONET (AErosol RObotic NETwork) Sun-photometer Cimel CE 318 measurements are used. The sites considered are: Barcelona (41.38º N, 2.17º E), Burjassot (39.51º N, 0.42º W), Cabo da Roca (38.78º N, 9.50º W), Évora (38.57º N, 7.91º W), Granada (37.16º N, 3.61º W) and Madrid (40.45º N, 3.72º W). In general, large aerosol optical depths (AOD) and low Ångström exponents (AE) are observed. An AOD of 2.0 at 675 nm is reached in several stations. Maximum values of AOD675 of 2.5 are registered in Évora. During and around the peak of AOD675, AEs close to 0 are measured. With regard to vertically-resolved aerosol optical properties, particle backscatter coefficients as high as 1.5∙10−5 m−1 sr−1 at 355 nm are recorded at every lidar stations. Mean lidar ratios are found in the range 40–55 sr at 355 nm and 34–61 sr at 532 nm during the event inside the dust layer. Mean particle and volume depolarization ratios are found to be very consistent between lidar stations. They range 0.19–0.31 and 0.12–0.26 respectively. The optical properties are also found very stable with height in the dust layer. Another remarkable aspect of the event is the limited height of the dust transport which is found between the ground and 5 km. Our vertically-resolved aerosol properties are also used to estimate the performances of two dust models, namely BSC-DREAM8b and NMMB/BSC-Dust, in order to evaluate their forecast skills in such intense dust outbreaks. We found that forecasts provided by the NMMB/BSC-Dust show a better agreement with observations than the ones from BSC-DREAM8b. The BSC-DREAM8b forecasts (24 h) present a large underestimation during the event. No clear degradation of the prognostics is appreciated in 24, 48, 72 h except for the Barcelona station.

scholarly journals EARLINET dust observations vs. BSC-DREAM8b modeled profiles: 12-year-long systematic comparison at Potenza, Italy

2014 ◽  
Vol 14 (16) ◽  
pp. 8781-8793 ◽  
Author(s):  
L. Mona ◽  
N. Papagiannopoulos ◽  
S. Basart ◽  
J. Baldasano ◽  
I. Binietoglou ◽  
...  
Keyword(s):  
Center Of Mass ◽  
Saharan Dust ◽  
Raman Lidar ◽  
Dust Layer ◽  
Systematic Comparison ◽  
Dust Extinction ◽  
Lidar Measurements ◽  
Order Of Magnitude ◽  
Lidar Ratio ◽  
532 Nm

Abstract. In this paper, we report the first systematic comparison of 12-year modeled dust extinction profiles vs. Raman lidar measurements. We use the BSC-DREAM8b model, one of the most widely used dust regional models in the Mediterranean, and Potenza EARLINET lidar profiles for Saharan dust cases, the largest one-site database of dust extinction profiles. A total of 310 dust cases were compared for the May 2000–July 2012 period. The model reconstructs the measured layers well: profiles are correlated within 5% of significance for 60% of the cases and the dust layer center of mass as measured by lidar and modeled by BSC-DREAM8b differ on average 0.3 ± 1.0 km. Events with a dust optical depth lower than 0.1 account for 70% of uncorrelated profiles. Although there is good agreement in terms of profile shape and the order of magnitude of extinction values, the model overestimates the occurrence of dust layer top above 10 km. Comparison with extinction profiles measured by the Raman lidar shows that BSC-DREAM8b typically underestimates the dust extinction coefficient, in particular below 3 km. Lowest model–observation differences (below 17%) correspond to a lidar ratio at 532 nm and Ångström exponent at 355/532 nm of 60 ± 13 and 0.1 ± 0.6 sr, respectively. These are in agreement with values typically observed and modeled for pure desert dust. However, the highest differences (higher than 85%) are typically related to greater Ångström values (0.5 ± 0.6), denoting smaller particles. All these aspects indicate that the level of agreement decreases with an increase in mixing/modification processes.

scholarly journals Observations of the spectral dependence of linear particle depolarization ratio of aerosols using NASA Langley airborne High Spectral Resolution Lidar

2015 ◽  
Vol 15 (23) ◽  
pp. 13453-13473 ◽  
Author(s):  
S. P. Burton ◽  
J. W. Hair ◽  
M. Kahnert ◽  
R. A. Ferrare ◽  
C. A. Hostetler ◽  
...  
Keyword(s):  
Case Studies ◽  
Spectral Resolution ◽  
Spectral Dependence ◽  
Saharan Dust ◽  
Spherical Particles ◽  
High Spectral Resolution ◽  
Depolarization Ratio ◽  
Dust Layer ◽  
High Spectral Resolution Lidar ◽  
532 Nm

Abstract. Linear particle depolarization ratio is presented for three case studies from the NASA Langley airborne High Spectral Resolution Lidar-2 HSRL-2). Particle depolarization ratio from lidar is an indicator of non-spherical particles and is sensitive to the fraction of non-spherical particles and their size. The HSRL-2 instrument measures depolarization at three wavelengths: 355, 532, and 1064 nm. The three measurement cases presented here include two cases of dust-dominated aerosol and one case of smoke aerosol. These cases have partial analogs in earlier HSRL-1 depolarization measurements at 532 and 1064 nm and in literature, but the availability of three wavelengths gives additional insight into different scenarios for non-spherical particles in the atmosphere. A case of transported Saharan dust has a spectral dependence with a peak of 0.30 at 532 nm with smaller particle depolarization ratios of 0.27 and 0.25 at 1064 and 355 nm, respectively. A case of aerosol containing locally generated wind-blown North American dust has a maximum of 0.38 at 1064 nm, decreasing to 0.37 and 0.24 at 532 and 355 nm, respectively. The cause of the maximum at 1064 nm is inferred to be very large particles that have not settled out of the dust layer. The smoke layer has the opposite spectral dependence, with the peak of 0.24 at 355 nm, decreasing to 0.09 and 0.02 at 532 and 1064 nm, respectively. The depolarization in the smoke case may be explained by the presence of coated soot aggregates. We note that in these specific case studies, the linear particle depolarization ratio for smoke and dust-dominated aerosol are more similar at 355 nm than at 532 nm, having possible implications for using the particle depolarization ratio at a single wavelength for aerosol typing.

scholarly journals Saharan dust infrared optical depth and altitude retrieved from AIRS: a focus over North Atlantic – comparison to MODIS and CALIPSO

2010 ◽  
Vol 10 (4) ◽  
pp. 1953-1967 ◽  
Author(s):  
S. Peyridieu ◽  
A. Chédin ◽  
D. Tanré ◽  
V. Capelle ◽  
C. Pierangelo ◽  
...  
Keyword(s):  
Optical Depth ◽  
North Atlantic ◽  
Western Indian Ocean ◽  
Saharan Dust ◽  
Orthogonal Polarization ◽  
Dust Layer ◽  
The North ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Good Agreement

Abstract. Monthly mean infrared (10 μm) dust layer aerosol optical depth (AOD) and mean altitude are simultaneously retrieved over the tropics (30° S–30° N) from almost seven years of Atmospheric Infrared Sounder (AIRS) observations covering the period January 2003 to September 2009. The method developed relies on the construction of look-up-tables computed for a large selection of atmospheric situations and follows two main steps: first, determination of the observed atmospheric thermodynamic situation and, second, determination of the dust properties. A very good agreement is found between AIRS-retrieved AODs and visible optical depths from the Moderate resolution Imaging Spectroradiometer (MODIS/Aqua) during the main (summer) dust season, in particular for three regions of the tropical North Atlantic and one region of the north-western Indian Ocean. Outside this season, differences are mostly due to the sensitivity of MODIS to aerosol species other than dust and to the more specific sensitivity of AIRS to the dust coarse mode. AIRS-retrieved dust layer mean altitudes are compared to the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP/CALIPSO) aerosol mean layer altitude for the period June 2006 to June 2009. Results for a region of the north tropical Atlantic downwind of the Sahara show a good agreement between the two products (σ≈360 m). Differences observed in the peak-to-trough seasonal amplitude, smaller from AIRS, are principally attributed to the large difference in spatial sampling of the two instruments. They also come from the intrinsic limit in sensitivity of the passive infrared sounders for low altitudes. These results demonstrate the capability of high resolution infrared sounders to measure not only dust aerosol AOD but also the mean dust layer altitude.

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