The depolarization - attenuated backscatter relation: CALIPSO lidar measurements vs. theory

Hu, Yongxiang; Vaughan, Mark; Liu, Zhaoyan; Lin, Bing; Yang, Ping; Flittner, D. E.; Hunt, Bill; Kuehn, Ralph E.; Huang, Jianping; Wu, Deliang; Rodier, Sharon; Powell, Kathleen A.; Trepte, Charles R.; Winker, David M.

doi:10.1364/oe.15.005327

Cited by 175 publications

(153 citation statements)

References 8 publications

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“…CALIOP acquires vertical profiles of elastic backscatter at two wavelengths (532 and 1064 nm) and linear depolarization at 532 nm from a near-nadir viewing geometry for both day and night (Hu et al, 2007a(Hu et al, , b, 2009Liu et al, 2008). The data sets detail the information of Level-1 backscatter, depolarization ratio, and colour ratio profiles along with the Level-2 Vertical Feature Mask (VFM) product and the 5 km aerosol profile product.…”

Section: Dust Detection Datamentioning

confidence: 99%

The relationship between anthropogenic dust and population over global semi-arid regions

et al. 2016

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Abstract. Although anthropogenic dust has received more attention from the climate research community, its dominant role in the production process is still not identified. In this study, we analysed the relationship between anthropogenic dust and population density/change over global semi-arid regions and found that semi-arid regions are major source regions in producing anthropogenic dust. The results showed that the relationship between anthropogenic dust and population is more obvious in cropland than in other land cover types (crop mosaics, grassland, and urbanized regions) and that the production of anthropogenic dust increases as the population density grows to more than 90 persons km −2 . Four selected semi-arid regions, namely East China, India, North America, and North Africa, were used to explore the relationship between anthropogenic dust production and regional population. The most significant relationship between anthropogenic dust and population occurred in an Indian semi-arid region that had a greater portion of cropland, and the high peak of anthropogenic dust probability appeared with 220 persons km −2 of population density and 60 persons km −2 of population change. These results suggest that the influence of population on production of anthropogenic dust in semi-arid regions is obvious in cropland regions. However, the impact does not always have a positive contribution to the production of anthropogenic dust, and overly excessive population will suppress the increase of anthropogenic dust. Moreover, radiative and climate effects of increasing anthropogenic dust need more investigation.

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Section: Dust Detection Datamentioning

confidence: 99%

The relationship between anthropogenic dust and population over global semi-arid regions

et al. 2016

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“…The strong backscatter coefficient at the cloud top indicates a liquid water layer and multiple-scattering effects (Hu et al, 2007). The cloud layer is optically too thick and attenuates the laser beam significantly, thus reliable lidar measurements are mainly limited to the upper cloud part.…”

Section: Liquid Water-phasementioning

confidence: 99%

Microphysical and optical properties of Arctic mixed-phase clouds. The 9 April 2007 case study.

Gayet

Mioche

Dörnbrack³

et al. 2009

Atmos. Chem. Phys.

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Abstract. Airborne measurements in Arctic boundarylayer stratocumulus were carried out near Spitsbergen on 9 April 2007 during the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign. A unique set of co-located observations is used to describe the cloud properties, including detailed in situ cloud microphysical and radiation measurements along with airborne and co-located spaceborne remote sensing data (CALIPSO lidar and CloudSat radar). CALIPSO profiles indicate cloud top levels at temperature between −24 • C and −21 • C. In situ measurements confirm that the cloud-top lidar attenuated backscatter signal along the aircraft trajectory is linked with the presence of liquid water, a common feature observed in Arctic mixedphase stratocumulus clouds. A low concentration of large ice crystals is also observed up to the cloud top resulting in significant CloudSat radar echoes. Since the ratio of the extinction of liquid water droplets to ice crystals is high, broadband radiative effects near the cloud top are mostly dominated by water droplets. CloudSat observations and in situ measurements reveal high reflectivity factors (up to 15 dBZ) and precipitation rates (1 mm h −1 ). This feature results from efficient ice growth processes. About 25% of the theoretically available liquid water is converted into ice water with large precipitating ice crystals. Using an estimate of mean cloud cover, a considerable value of 10 6 m 3 h −1 of fresh water could be settled over the Greenland sea pool. European Centre for Medium-Range Weather Forecast (ECMWF) operational analyses reproduces the boundary layer height variation along the flight track. However, small-scale featuresCorrespondence to: J.-F. Gayet (gayet@opgc.univ-bpclermont.fr) in the observed cloud field cannot be resolved by ECMWF analysis. Furthermore, ECMWF's diagnostic partitioning of the condensed water into ice and liquid reveals serious shortcomings for Arctic mixed-phased clouds. Too much ice is modelled.

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“…Liu et al (2008) studied vertical profiles of atmospheric dust in the Ganganagar, Taklimakan and Gobi desert regions using the CALIPSO lidar and found depolarization ratios as high as 0.3 for dust in the lower layers of the atmosphere. Hu et al (2007) and later, Cho et al (2008) illustrated a relationship between CALIPSO derived depolarization ratio and backscattering intensities for nonspherical particles. They showed that ice crystals can have depolarization ratios ranging from 0.1 to 0.5 with varying backscatter intensities.…”

Section: Introductionmentioning

confidence: 93%

Single Particle Measurements of the Optical Properties of Small Ice Crystals and Heterogeneous Ice Nuclei

Glen

Brooks

2014

Aerosol Science and Technology

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Dust aerosol and ice crystals are two major types of nonspherical particles in the atmosphere which have significant roles in cloud-aerosol interactions and the radiative budget. The presence of dust and ice often coincide in the atmosphere because dust particles are efficient ice nuclei. The size and composition dependence of the scattering properties of dust and ice are needed to assess their individual contributions to the optical scattering of sunlight. Here we present a new measurement technique used to determine the single particle forward scattering, backscattering, and depolarization ratio (at a wavelength of 680 nm) for representative nonspherical atmospheric particles. The Texas A&M University Continuous Flow Diffusion Chamber (CFDC) was used as an ice crystal generator to produce ice crystals via both homogenous and heterogeneous nucleation mechanisms under well-controlled laboratory conditions. Optical scattering properties of mineral dusts and small ice crystals (0.6 mm to 50 mm optical diameter) were measured by the Droplet Measurement Technologies, Inc. (DMT) Cloud Aerosol Spectrometer with Polarization (CASPOL). Significant differences between the optical properties of single dusts and ice particles of the same size were observed. Differences between the optical signatures of homogeneously and heterogeneously nucleated ice crystals were not statistically significant. Our results suggest that atmospheric ice crystals can be identified and quantified independently from the dust particles on which they form based on analysis of their backscatter and depolarization signals.

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The depolarization - attenuated backscatter relation: CALIPSO lidar measurements vs. theory

Cited by 175 publications

References 8 publications

The relationship between anthropogenic dust and population over global semi-arid regions

The relationship between anthropogenic dust and population over global semi-arid regions

Microphysical and optical properties of Arctic mixed-phase clouds. The 9 April 2007 case study.

Single Particle Measurements of the Optical Properties of Small Ice Crystals and Heterogeneous Ice Nuclei

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