How much of the global aerosol optical depth is found in the boundary layer and free troposphere?

Bourgeois, Quentin; Ekman, Annica M. L.; Renard, Jean‐Baptiste; Krejci, Radovan; Devasthale, Abhay; Bender, Frida A.‐M.; Riipinen, Ilona; Berthet, Gwenaël; Tackett, Jason L.

doi:10.5194/acp-2017-1058

Cited by 5 publications

(6 citation statements)

References 17 publications

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“…Dust aerosols can be lifted up to 5 km over the Arabian Peninsula and then transported to the Arabian Sea at a higher altitude of up to 6 km. The dust layers at high altitude over the Arabian Sea in this case study are consistent with findings of Bourgeois et al () that the dust aerosols in the free troposphere dominate the total AOD over the Arabian Sea in the boreal summer. This could be attributed to the confluence of the strong southwesterly summer monsoon flow over ocean and the northwesterly Shamal winds, which could result in strong uplift and accumulation of dust aerosols over the Arabian Sea.…”

Section: Resultssupporting

confidence: 92%

“…The AOD over the Arabian Sea has strong seasonal variations: it peaks in the boreal summer, followed by fall, spring, and winter in the decreasing order, which is consistent with the sea salt seasonal variations but different from the dust seasonal variations documented by Tindale and Pease (). It should be noted that CALIPSO AOD is larger during night time than during day time, which is probably due to high signal‐to‐noise ratio during night time (Bourgeois et al, ).…”

Section: Resultsmentioning

confidence: 99%

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High Summertime Aerosol Loadings Over the Arabian Sea and Their Transport Pathways

Jin

Wei

et al. 2018

JGR Atmospheres

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Satellite observations show high aerosol loadings over the Arabian Sea in boreal summer, which have great impacts on the Indian monsoon due to absorbing dust aerosols. However, the compositions, origins, transport pathways, and decadal trends of these aerosols have not been well studied. In this study, using multiple satellite retrievals, a back trajectory model, and reanalysis data, we found that (1) aerosol optical depth (AOD) over the Arabian Sea and Arabian Peninsula have a summer peak and dust aerosols dominate the AOD; aerosol reanalysis data tend to considerably underestimate dust AOD compared to satellite data, indicating challenges of extracting dust from total AOD; (2) aerosols over the Arabian Sea are largely transported from South and East Arabian Peninsula by cyclonic winds in the lower troposphere (850 hPa) and from Iran–Afghanistan–Pakistan by anticyclonic winds in the middle troposphere (500 hPa); (3) both case studies and composite analyses show that extremely high aerosol loadings over the Arabian Sea is associated with an abnormally low pressure over the Arabian Sea and the Middle East; and (4) significant positive trends in AOD over the Arabian Peninsula and the Arabian Sea exist during 2000–2011 but disappear during 2000–2016, indicating a strong interdecadal variability of dust activities. This study revealed pathways linking dust emissions in the Middle East to high summertime AOD over the Arabian Sea and identified the atmospheric conditions favorable for dust emissions and transport.

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Section: Resultssupporting

confidence: 92%

Section: Resultsmentioning

confidence: 99%

High Summertime Aerosol Loadings Over the Arabian Sea and Their Transport Pathways

Jin

Wei

et al. 2018

JGR Atmospheres

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“…Interestingly, vast areas over the ocean feature AOD fractions of less than 40%, suggesting a significant contribution of free tropospheric aerosols to the total AOD. These results are qualitatively consistent with the results Bourgeois et al (2018) using CALIPSO version 4.1.…”

Section: Fractional Caliop-soda Aod At 532 Nm In the Marine Boundary supporting

confidence: 91%

Novel aerosol extinction coefficients and lidar ratios over the ocean from CALIPSO-CloudSat: Evaluation and global statistics

Painemal¹,

Clayton²,

Ferrare³

et al. 2018

Preprint

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Abstract. Aerosol extinction coefficients (σa) and lidar ratios (LR) are retrieved over the ocean from CALIOP attenuated backscatter profiles by solving the lidar equation constrained with aerosol optical depths (AOD) derived by applying the Synergized Optical Depth of Aerosols (SODA) algorithm to ocean surface returns measured by CALIOP and CloudSat’s Cloud Profiling Radar. σa and LR are retrieved for two independent scenarios that require somewhat different assumptions: a) a single homogeneous atmospheric layer (1L) for which the LR is constant with height, and b) a vertically homogeneous layer with a constant LR overlying a marine boundary layer with a homogenous LR fixed at 25 sr (2-layer method, 2L). These new retrievals differ from the standard CALIPSO version 4.1 (V4) product, as the CALIOP-SODA method does not rely on an aerosol classification scheme to select LR. CALIOP-SODA σa and LR are evaluated using airborne high spectral resolution lidar (HSRL) observations over the northwest Atlantic. CALIOP-SODA LR (1L and 2L) positively correlates with its HSRL counterpart (linear correlation coefficient r > 0.67), with a negative bias smaller than 13.2 %, and a good agreement for σa (r ≥ 0.78) with a small negative bias (≤|−9.2 %|). Furthermore, a global comparison of optical depths derived by CALIOP SODA and CALIPSO V4 reveals substantial differences over regions dominated by dust and smoke, in qualitative agreement with previously reported discrepancies between MODIS and CALIPSO AOD. Global maps of CALIOP-SODA LR feature high values over littoral zones, consistent with expectations of continental aerosol transport offshore. In addition, seasonal transitions associated with biomass burning during June to October over the southeast Atlantic are well reproduced by CALIOP-SODA LR.

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“…Interestingly, vast areas over the ocean feature AOD fractions of less than 40 %, suggesting a significant contribution of free tropospheric aerosols to the total AOD. These results are qualitatively consistent with the results of Bourgeois et al (2018) using CALIPSO version 4.1.…”

Section: Maps Of Caliop-soda Lidar Ratio (Lr) At 532 Nmsupporting

confidence: 90%

Reply, Referee #2

Painemal¹

2019

Preprint

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Aerosol extinction coefficients (σ a ) and lidar ratios (LRs) are retrieved over the ocean from CALIPSO's Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) attenuated backscatter profiles by solving the lidar equation constrained with aerosol optical depths (AODs) derived by applying the Synergized Optical Depth of Aerosols (SODA) algorithm to ocean surface returns measured by CALIOP and CloudSat's Cloud Profiling Radar. σ a and LR are retrieved for two independent scenarios that require somewhat different assumptions: (a) a single homogeneous atmospheric layer (1L) for which the LR is constant with height and (b) a vertically homogeneous layer with a constant LR overlying a marine boundary layer with a homogenous LR fixed at 25 sr (two-layer method, 2L). These new retrievals differ from the standard CALIPSO version 4.1 (V4) product, as the CALIOP-SODA method does not rely on an aerosol classification scheme to select LR. CALIOP-SODA σ a and LR are evaluated using airborne high-spectral-resolution lidar (HSRL) observations over the northwest Atlantic. CALIOP-SODA LR (1L and 2L) positively correlates with its HSRL counterpart (linear correlation coefficient r > 0.67), with a negative bias smaller than 17.4 % and a good agreement for σ a (r ≥0.78) with a small negative bias (≤ | − 9.2 %|). Furthermore, a global comparison of optical depths derived by CALIOP-SODA and CALIPSO V4 reveals substantial discrepancies over regions dominated by dust and smoke (0.24), whereas Aqua's Moderate resolution Imaging Spectroradiometer (MODIS) and SODA AOD regional differences are within 0.06.Global maps of CALIOP-SODA LR feature high values over littoral zones, consistent with expectations of continen-tal aerosol transport offshore. In addition, seasonal transitions associated with biomass burning from June to October over the southeast Atlantic are well reproduced by CALIOP-SODA LR.

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How much of the global aerosol optical depth is found in the boundary layer and free troposphere?

Cited by 5 publications

References 17 publications

High Summertime Aerosol Loadings Over the Arabian Sea and Their Transport Pathways

High Summertime Aerosol Loadings Over the Arabian Sea and Their Transport Pathways

Novel aerosol extinction coefficients and lidar ratios over the ocean from CALIPSO-CloudSat: Evaluation and global statistics

Reply, Referee #2

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