Preferential settling of elongated mineral dust particles in the atmosphere

Li, Jingmin; Osada, Kazuo

doi:10.1029/2007gl030262

Cited by 28 publications

(28 citation statements)

References 20 publications

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“…We argue that the lack of a distinct effect due to dust non-spherical particle phase functions on our retrieval (as shown in Fig. 6) appears consistent with the findings by Li and Osada (2007), who showed that only spherical dust particles are persistent downwind of desert regions, because of the preferential settling of elongated dust particles.…”

Section: Discussionsupporting

confidence: 79%

Improved algorithm for MODIS satellite retrievals of aerosol optical thickness over land in dusty atmosphere: Implications for air quality monitoring in China

Wang

Spurr

et al. 2010

Remote Sensing of Environment

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Wang, Jun; Xu, Xiaoguang; Spurr, R.; Wang, Yuxuang; and Drury, Easan, "Improved algorithm for MODIS satellite retrievals of aerosol optical thickness over land in dusty atmosphere: Implications for air quality monitoring in China" (2010 A new algorithm, using the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite reflectance and aerosol single scattering properties simulated from a chemistry transport model (GEOS-Chem), is developed to retrieve aerosol optical thickness (AOT) over land in China during the spring dust season. The algorithm first uses a "dynamic lower envelope" approach to sample the MODIS dark-pixel reflectance data in low AOT conditions, to derive the local surface visible (0.65 μm)/near infrared (NIR, 2.1 μm) reflectance ratio. Joint retrievals of AOT at 0.65 μm and surface reflectance at 2.1 μm are then performed, based on the time, location, and spectraldependent single scattering properties of the dusty atmosphere as simulated by the GEOS-Chem. A linearized vector radiative transfer model (VLIDORT) that simultaneously computes the top-of-atmosphere reflectance and its Jacobian with respect to AOT, is used in the forward component of the inversion of MODIS reflectance to AOT. Comparison of retrieved AOT results in April and May of 2008 with AERONET observations shows a strong correlation (R = 0.83), with small bias (0.01), and small RMSE (0.17); the figures are a substantial improvement over corresponding values obtained with the MODIS Collection 5 AOT algorithm for the same study region and time period. The small bias is partially due to the consideration of dust effect at 2.1 μm channel, without which the bias is − 0.05. The surface PM 10 (particulate matter with diameter less than 10 μm) concentrations derived using this improved AOT retrieval show better agreement with ground observations than those derived from GEOSChem simulations alone, or those inferred from the MODIS Collection 5 AOT. This study underscores the value of using satellite reflectance to improve the air quality modeling and monitoring.

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Section: Discussionsupporting

confidence: 79%

Improved algorithm for MODIS satellite retrievals of aerosol optical thickness over land in dusty atmosphere: Implications for air quality monitoring in China

Wang

Spurr

et al. 2010

Remote Sensing of Environment

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“…The only other evidence for the alignment that we have been able to locate comes, indirectly, from analysis of deposited dust, which indicates that particles with high aspect ratios are preferentially removed from dust transported over longer distances (Li and Osada, 2007). In a companion article Li and Osada (2007a) explain the apparently increased settling rates of high aspect ratio particles by invoking vertical alignment, which would lead to reduced viscous drag. The authors then ascribe the alignment to flow shear.…”

Section: Discussionmentioning

confidence: 99%

Alignment of atmospheric mineral dust due to electric field

et al. 2007

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Abstract. Optical polarimetry observations on La Palma, Canary Islands, during a Saharan dust episode show dichroic extinction indicating the presence of vertically aligned particles in the atmosphere. Modelling of the extinction together with particle orientation indicates that the alignment could have been due to an electric field of the order of 2 kV/m. Two alternative mechanisms for the origin of the field are examined: the effect of reduced atmospheric conductivity and charging of the dust layer, the latter effect being a more likely candidate. It is concluded that partial alignment may be a common feature of Saharan dust layers. The modelling indicates that the alignment can significantly alter dust optical depth. This "Venetian blind effect" may have decreased optical thickness in the vertical direction by as much as 10% for the case reported here. It is also possible that the alignment and the electric field modify dust transport.

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“…[17] Applying settling velocities from Li and Osada [2007] in the absence of turbulence, giant mode particles would fall the 5 km SABL depth within 12.5 AE 4 h. This explains the loss of giant particles between the fresh and aged profiles (Figure 1c) in all cases, except for flight b604 where giant particles were transported over longer time scales, perhaps due to overnight turbulence in cold-pool outflow. Deposition also plays a role for coarse mode Figure 1.…”

Section: Mechanisms For Size Distribution Changementioning

confidence: 99%

Impact of atmospheric transport on the evolution of microphysical and optical properties of Saharan dust

Ryder

Highwood

Lai

et al. 2013

Geophysical Research Letters

123

147

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Saharan dust affects the climate by altering the radiation balance and by depositing minerals to the Atlantic Ocean. Both are dependent on particle size. We present aircraft measurements comprising 42 profiles of size distribution (0.1–300 µm), representing freshly uplifted dust, regional aged dust, and dust in the Saharan Air Layer (SAL) over the Canary Islands. The mean effective diameter of dust in SAL profiles is 4.5 µm smaller than that in freshly uplifted dust, while the vertical structure changes from a low shallow layer (0–1.5 km) to a well‐mixed deep Saharan dust layer (0–5 km). Size distributions show a loss of 60 to 90% of particles larger than 30 µm 12 h after uplift. The single scattering albedo (SSA) increases from 0.92 to 0.94 to 0.95 between fresh, aged, and SAL profiles: this is enough to alter heating rates by 26%. Some fresh dust close to the surface shows SSA as low as 0.85.

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Preferential settling of elongated mineral dust particles in the atmosphere

Cited by 28 publications

References 20 publications

Improved algorithm for MODIS satellite retrievals of aerosol optical thickness over land in dusty atmosphere: Implications for air quality monitoring in China

Improved algorithm for MODIS satellite retrievals of aerosol optical thickness over land in dusty atmosphere: Implications for air quality monitoring in China

Alignment of atmospheric mineral dust due to electric field

Impact of atmospheric transport on the evolution of microphysical and optical properties of Saharan dust

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