Optical and microphysical characterization of aerosol layers over South
Africa by means of multi-wavelength depolarization and Raman lidar
measurements

Giannakaki, Elina; Zyl, P. G. van; Müller, Detlef; Balis, Dimitris; Komppula, Mika

doi:10.5194/acp-16-8109-2016

Cited by 61 publications

(61 citation statements)

References 75 publications

(73 reference statements)

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“…Compared to premonsoon, the S MODIS and S MODEL are significantly higher (twofold) than the S CALIPSO (~30 sr) during winter. It should be noted that the outflow of anthropogenic aerosols from South Asia to the Bay of Bengal takes place during winter, and these anthropogenic aerosols have higher lidar ratio as reported by several investigators through ship‐borne and island measurements (Cattrall et al, ; Giannakaki et al, ). The lidar ratio estimated from the semiempirical approach ( S MODEL ) further support the values estimated using MODIS AOD measurements.…”

Section: Data Set and Methodologymentioning

confidence: 99%

Vertical Structure of Aerosols and Mineral Dust Over the Bay of Bengal From Multisatellite Observations

2017

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The vertical distribution of aerosol and dust extinction coefficient over the Bay of Bengal is examined using the satellite observations (Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) and Moderate Resolution Imaging Spectroradiometer (MODIS)) for the period from 2006 to 2017. Distinct seasonal pattern is observed in the vertical structure of both aerosol and dust over the Bay of Bengal with an enhancement of 24% in the aerosol extinction above 1 km from winter (December, January and February) to premonsoon (March, April, and May). Significant contribution of dust is observed over the northern Bay of Bengal during premonsoon season where 22% of the total aerosol extinction is contributed by dust aerosols transported from the nearby continental regions. During winter, dust transport is found to be less significant with fractional contribution of ~10%–13% to the total aerosol optical depth over the Bay of Bengal. MODIS‐derived dust fraction (fine mode based) shows an overestimation up to twofold compared to CALIOP dust fraction (depolarization based), whereas the Goddard Chemistry Aerosol Radiation and Transport‐simulated dust fraction underestimates the satellite‐derived dust fractions over the Bay of Bengal. Though the long‐term variation in dust aerosol showed a decreasing trend over the Bay of Bengal, the confidence level is insufficient in establishing the robustness of the observed trend. However, significant dust‐induced heating is observed above the boundary layer during premonsoon season. This dust‐induced elevated heating can affect the convection over the Bay of Bengal which will have implication on the monsoon dynamics over the Indian region.

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Section: Data Set and Methodologymentioning

confidence: 99%

Vertical Structure of Aerosols and Mineral Dust Over the Bay of Bengal From Multisatellite Observations

2017

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“…Firstly, the signal-to-noise ratio (SNR; Eq. 1) is calculated according to the following equation (Georgousis et al, 2016):…”

Section: Instrument and Measuring Sitesmentioning

confidence: 99%

Variability in cirrus cloud properties using a Polly<sup>XT</sup> Raman lidar over high and tropical latitudes

et al. 2020

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Measurements of geometrical and optical properties of cirrus clouds, performed with a multi-wavelength Polly XT Raman lidar during the period 2008 to 2016, are analysed. The measurements were performed with the same instrument, during sequential periods, in three places at different latitudes, Gwal Pahari (28.43 • N, 77.15 • E; 243 m a.s.l.) in India, Elandsfontein (26.25 • S, 29.43 • E; 1745 m a.s.l.) in South Africa and Kuopio (62.74 • N, 27.54 • E ; 190 m a.s.l.) in Finland. The lidar dataset was processed by an automatic cirrus cloud masking algorithm, developed in the frame of this work. In the following, we present a statistical analysis of the lidar-retrieved geometrical characteristics (cloud boundaries, geometrical thickness) and optical properties of cirrus clouds (cloud optical depth, lidar ratio, ice crystal depolarisation ratio) measured over the three areas that correspond to subtropical and subarctic regions as well as their seasonal variability. The effect of multiple scattering from ice particles to the derived optical products is also considered and corrected in this study. Our results show that cirrus layers, which have a noticeable monthly variability, were observed between 6.5 and 13 km, with temperatures ranging from −72 to −27 • C. The observed differences on cirrus clouds' geometrical and optical properties over the three regions are discussed in terms of latitudinal and temperature dependence. The latitudinal dependence of the geometrical properties is consistent with satellite observations, following the pattern observed with CloudSat, with decreasing values towards the poles. The geometrical boundaries have their highest values in the subtropical regions, and overall, our results seem to demonstrate that subarctic cirrus clouds are colder, lower and optically thinner than subtropical cirrus clouds. The dependence of cirrus cloud geometrical thickness and optical properties on mid-cirrus temperatures shows a quite similar tendency for the three sites but less variability for the subarctic dataset. Cirrus clouds are geometrically and optically thicker at temperatures between −45 and −35 • C, and a second peak is observed at lower temperatures ∼ −70 • C for the subarctic site. Lidar ratio values also exhibit a pattern, showing higher values moving toward the poles, with higher mean values observed over the subarctic site. The dependency of the mid-cirrus temperatures on the lidar ratio values and the particle depolarisation values is further examined. Our study shows that the highest values of the cirrus lidar ratio correspond to higher values of cirrus depolarisation and warmer cirrus. The kind of information presented here can be rather useful in the cirrus parameterisations required as input to radiative transfer models and can be a complementary tool for satellite products that cannot provide cloud vertical structure. In addition, ground-based statistics of the cirrus properties could be useful in the validation and improvement of the corresponding derived products from satellite retr...

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“…The lidar has been employed under various campaigns and locations over the course of years. Among others, two long-term aerosol experimental campaigns at Gual Pahari, India (Komppula et al, 2012) and Elandsfontein, South Africa (Giannakaki et al, 2015(Giannakaki et al, , 2016Korhonen et al, 2014) and at the permanent measurement site in Vehmasmäki, Finland (Bohlmann et al, 2019;Filioglou et al, 2017) have been conducted. The system is also part of the Finnish lidar network (Hirsikko et al, 2014), the European Aerosol Research Lidar Network (EARLINET) (Bösenberg et al, 2003;Pappalardo et al, 2014) and PollyNET (Baars et al, 2016) which is an independent Raman and polarization lidar network where measurements from all member-stations are visualized through "quick looks", publicly available on the web page of PollyNET (http://polly.tropos.de).…”

Section: The Multi-wavelength Raman Lidar Fmi -Polly Xtmentioning

confidence: 99%

Optical and geometrical aerosol particle properties over the United Arab Emirates

Filioglou¹,

Giannakaki²,

Backman³

et al. 2020

Preprint

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Abstract. One-year of ground-based night-time Raman lidar observations have been analysed under the Optimization of Aerosol Seeding In rain enhancement Strategies (OASIS) project, in order to characterize the aerosol particle properties over a rural site in the United Arab Emirates. In total, 1130 aerosol particle layers were detected during the one-year measurement campaign which took place between March 2018 and February 2019. Several subsequent aerosol layers could be observed simultaneously in the atmosphere up to 11 km. The observations indicate that the measurement site is a receptor of frequent dust events but predominantly the dust is mixed with aerosols of anthropogenic and/or marine origin. The mean aerosol optical depth over the measurement site ranged at 0.37 ± 0.12 and 0.21 ± 0.11 for the 355 and 532 nm, respectively. Moreover, a mean lidar ratio of 43 ± 11 sr at a wavelength of 355 nm and 39 ± 10 sr at 532 nm was found. The average linear particle depolarization ratio measured over the course of the campaign was 15 ± 6 % and 19 ± 7 % at 355 nm and 532 nm wavelengths, respectively. Since the region is both a source and a receptor of mineral dust, we have also explored the properties of Arabian mineral dust of the greater area of United Arab of Emirates and the Arabian Peninsula. The observed Arabian dust particle properties were 45 ± 5 (42 ± 5) sr at 355 (532) nm for the lidar ratio, 25 ± 2 % (31 ± 2 %) for the linear particle depolarization ratio at 355 (532) nm, and 0.3 ± 0.2 (0.2 ± 0.2) for the extinction‑related Ångström exponent (backscatter‑related Ångström exponent) between 355 and 532 nm. This study is the first to report comprehensive optical properties of the Arabian dust particles based on long term observations, using at the fullest the capabilities of a multi wavelength Raman lidar instrument. The results suggest that the mineral dust properties over the Middle East and western Asia, including the observation site, are comparable to those of African mineral dust with regard to the particle depolarization ratios but not for lidar ratios. The smaller lidar ratio values in this study compared to the reference studies are attributed to the difference in the geochemical characteristics of the soil originating in the study region compared to Northern Africa.

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Optical and microphysical characterization of aerosol layers over South Africa by means of multi-wavelength depolarization and Raman lidar measurements

Cited by 61 publications

References 75 publications

Vertical Structure of Aerosols and Mineral Dust Over the Bay of Bengal From Multisatellite Observations

Vertical Structure of Aerosols and Mineral Dust Over the Bay of Bengal From Multisatellite Observations

Variability in cirrus cloud properties using a Polly<sup>XT</sup> Raman lidar over high and tropical latitudes

Optical and geometrical aerosol particle properties over the United Arab Emirates

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Optical and microphysical characterization of aerosol layers over South Africa by means of multi-wavelength depolarization and Raman lidar measurements

Cited by 61 publications

References 75 publications

Vertical Structure of Aerosols and Mineral Dust Over the Bay of Bengal From Multisatellite Observations

Vertical Structure of Aerosols and Mineral Dust Over the Bay of Bengal From Multisatellite Observations

Variability in cirrus cloud properties using a Polly&lt;sup&gt;XT&lt;/sup&gt; Raman lidar over high and tropical latitudes

Optical and geometrical aerosol particle properties over the United Arab Emirates

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Variability in cirrus cloud properties using a Polly<sup>XT</sup> Raman lidar over high and tropical latitudes