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  • 1
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    A new study of sea spray optical properties from multi-sensor spaceborne observations (2014)
    Copernicus
    Details
    Publication Date: 2014-01-06
    Description: Retrievals of aerosol optical depth (AOD) from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite sensor require the assumption of an extinction-to-backscatter ratio, also known as the lidar ratio. This paper evaluates a new method to calculate the lidar ratio of sea spray aerosol using two independent sources: the AOD from the Synergized Optical Depth of Aerosols (SODA) algorithm and the integrated attenuated backscatter from CALIOP. With this method, the particulate lidar ratio can be derived for individual CALIOP retrievals in single aerosol layer columns over the ocean. Global analyses are carried out using CALIOP level 2, 5 km sea spray aerosol layer products and the collocated SODA nighttime data from December 2007 to December 2009. The global mean lidar ratio for sea spray aerosols was found to be 26 sr, roughly 30% higher than the current value prescribed by CALIOP standard retrieval algorithm. Data analysis also showed considerable spatiotemporal variability in the calculated lidar ratio over the remote oceans. The calculated aerosol lidar ratios are shown to be inversely related to the mean ocean surface wind speed: increase in ocean surface wind speed (U10) from 0 to 〉15 m s−1 reduces the mean lidar ratios for sea spray particles from 32 sr (for 015 m s−1). Such changes in the lidar ratio are expected to have a corresponding effect on the sea spray AOD. The outcomes of this study are relevant for future improvements of the SODA and CALIOP operational product and could lead to more accurate retrievals of sea spray AOD.
    Electronic ISSN: 1680-7375
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 2
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    Influence of measurement uncertainties on soluble aerosol iron over the oceans (2015)
    Copernicus
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    Publication Date: 2015-09-01
    Description: The atmospheric supply of dust iron (Fe) plays a crucial role in the Earth's biogeochemical cycle and is of specific importance as a micronutrient in the marine environment. Observations show several orders of magnitude variability in the fractional solubility of Fe in dust aerosols, making it hard to assess the role of mineral dust for global ocean biogeochemical Fe cycle. In this study we compare the operational solubility of dust aerosol Fe associated with one of the flow-through leaching protocols to the results of the global 3-D chemical transport model GEOS-Chem. In the protocol aerosol Fe is defined soluble by first deionized water leaching of mineral dust through a 0.45 μm pore size membrane followed by acidification and storage of the leachate over a long period of time prior to the analysis. To assess the concentrations of soluble Fe inferred by this flow-through leaching protocol we are using in situ measurements of dust size distribution with the prescribed of 50 % fractional solubility of Fe in less than 0.45 μm sized dust particles collected in the leachate. In the model, the fractional solubility of Fe is either explicitly calculated using complex dust Fe dissolution module, or prescribed to be 1 and 4 %. Calculations show that the fractional solubility of Fe derived through the flow-through leaching is typically higher compared to the model results. The largest differences (〉30 %) are predicted to occur farther away from the dust source regions, over the areas where sub-0.45 μm sized mineral dust particles contribute a larger fraction of the total dust mass. This study suggests that inconsistences in the operational definition of soluble Fe could contribute to the wide range of the fractional solubility of dust aerosol Fe reported in the literature.
    Print ISSN: 1810-6277
    Electronic ISSN: 1810-6285
    Topics: Biology , Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 3
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    Spaceborne observations of the lidar ratio of marine aerosols (2015)
    Copernicus
    Details
    Publication Date: 2015-03-23
    Description: Retrievals of aerosol optical depth (AOD) from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite sensor require the assumption of the extinction-to-backscatter ratio, also known as the lidar ratio. This paper evaluates a new method to calculate the lidar ratio of marine aerosols using two independent sources: the AOD from the Synergized Optical Depth of Aerosols (SODA) project and the integrated attenuated backscatter from CALIOP. With this method, the particulate lidar ratio can be derived for individual CALIOP retrievals in single aerosol layer, cloud-free columns over the ocean. Global analyses are carried out using CALIOP level 2, 5 km marine aerosol layer products and the collocated SODA nighttime data from December 2007 to November 2010. The global mean lidar ratio for marine aerosols was found to be 26 sr, roughly 30% higher than the current value prescribed by the CALIOP standard retrieval algorithm. Data analysis also showed considerable spatiotemporal variability in the calculated lidar ratio over the remote oceans. The calculated marine aerosol lidar ratio is found to vary with the mean ocean surface wind speed (U10). An increase in U10 reduces the mean lidar ratio for marine regions from 32 ± 17 sr (for 0 〈 U10 〈 4 m s−1) to 22 ± 7 sr (for U10 〉 15 m s−1). Such changes in the lidar ratio are expected to have a corresponding effect on the marine AOD from CALIOP. The outcomes of this study are relevant for future improvements of the SODA and CALIOP operational product and could lead to more accurate retrievals of marine AOD.
    Print ISSN: 1680-7316
    Electronic ISSN: 1680-7324
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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