Wavelength dependence of the optical depth of biomass burning, urban, and desert dust aerosols

Eck, T. F.; Holben, B. N.; Reid, Jeffrey S.; Dubovik, Оleg; Smirnov, A.; O’Neill, N. T.; Slutsker, I.; Kinne, Stefan

doi:10.1029/1999jd900923

Cited by 1,988 publications

(1,839 citation statements)

References 37 publications

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“…The data were then sorted with respect to the time to the nearest cloud, and the ensemble mean AOD and Angstrom exponent were calculated as a function of this interval. Angstrom exponent is defined using two wavelengths (440 nm and 870 nm), and is a measure of particle size (Eck et al, 1999).…”

Section: Discussionmentioning

confidence: 99%

On the twilight zone between clouds and aerosols

Koren

Remer

Kaufman

et al. 2007

Geophysical Research Letters

312

365

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[1] Cloud and aerosols interact and form a complex system leading to high uncertainty in understanding climate change. To simplify this non-linear system it is customary to distinguish between ''cloudy'' and ''cloud-free'' areas and measure them separately. However, we find that clouds are surrounded by a ''twilight zone'' -a belt of forming and evaporating cloud fragments and hydrated aerosols extending tens of kilometers from the clouds into the socalled cloud-free zone. The gradual transition from cloudy to dry atmosphere is proportional to the aerosol loading, suggesting an additional aerosol effect on the composition and radiation fluxes of the atmosphere. Using AERONET data, we find that the measured aerosol optical depth is higher by 13% ± 2% in the visible and 22% ± 2% in the NIR in measurements taken near clouds relative to its value in the measurements taken before or after, and that 30%À60% of the free atmosphere is affected by this phenomenon.

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Section: Discussionmentioning

confidence: 99%

On the twilight zone between clouds and aerosols

Koren

Remer

Kaufman

et al. 2007

Geophysical Research Letters

312

365

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“…The AERONET and Microtops sunphotometer AODs generally agree to within 0.07 and there are no obvious systematic differences between the two instruments. The differences in AOD between AERONET and Microtops are probably due to differences in the location of the instruments, since instrumental uncertainties in sunphotometer AODs are not expected to be more than 0.02 (Eck et al, 1999;Ichoku et al, 2002). Figures 5 and 6 show a fair degree of variability in AOD, which may be due to horizontal variability of the AOD since the Banizoumbou AERONET site was approximately 50 km to the northeast of Niamey where the Microtops measurements were made.…”

Section: Vertical Distribution Of Aerosol and Thermodynamic Variablesmentioning

confidence: 97%

Measurements of aerosol properties from aircraft, satellite and ground‐based remote sensing: a case‐study from the Dust and Biomass‐burning Experiment (DABEX)

Johnson

Christopher

Haywood

et al. 2009

Quart J Royal Meteoro Soc

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This paper presents aircraft measurements of aerosol optical properties and radiative effects from the Dust and Biomass-burning Experiment (DABEX) over West Africa. On 19 January 2006 cloud-free skies and high aerosol loading provided ideal conditions for an intercomparison of aircraft, satellite and ground-based remote sensing instruments. Aerosol size distributions, optical properties, aerosol optical depth (AOD) and downwelling solar radiation were measured by the UK FAAM aircraft in the region of Niamey, Niger. The aircraft in situ measurements showed a mixture of dust and biomass-burning aerosols and indicated an AOD of 0.79 (at 550 nm) that compared well against AODs from the Banizoumbou Aerosol Robotic Network (AERONET) site (0.74) and a Microtops sunphotometer (0.72). AERONET size distributions showed a good degree of similarity with the aircraft in situ measurements. AERONET single-scattering albedos were also in fairly close agreement with the aircraft, having values of 0.85 and 0.87, respectively (at 550 nm). Measurements of downwelling solar radiation from the aircraft compared well with measurements from the Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) at Niamey. Radiative transfer modelling suggested a 130-160 W m −2 instantaneous reduction of downwelling solar radiation by the aerosol column (15-18% of the total flux). Measurements of downwelling solar radiation compared reasonably well against radiative transfer modelling based on the aircraft in situ data. Satellite retrievals of AOD from MISR and MODIS Deep Blue were within 0.05 of the ground-based sunphotometers measurements although there were discrepancies in optical properties retrieved by MISR, as compared to AERONET and the aircraft.

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“…The version 3 AERONET data also tend to have less thin cirrus contamination and better quality-control algorithms than does version 2. The AOD uncertainty in version 3 Level 2 data is practically the same as in Version 2, which is ~0.01 in the visible and near-infrared wavelengths and increasing to ~0.02 in the UV (Eck et al, 1999). Cloud screening in Version 3 is briefly described in Eck et al (2018) and in depth in a future paper (D. Giles personal communication).…”

Section: Aeronet Sun/sky Aerosol Productsmentioning

confidence: 92%

Characterizing the 2015 Indonesia Fire Event Using Modified MODIS Aerosol Retrievals

Shi¹,

Levy²,

Eck³

et al. 2018

Preprint

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Abstract. The Indonesian fire and smoke event of 2015 was an extreme episode that affected public health and caused severe economic and environmental damage. The MODIS Dark Target (DT) aerosol algorithm, developed for global applications, significantly underestimated regional aerosol optical depth (AOD) during this episode. The larger-than-globalaveraged uncertainties in DT product over this event were due to both an overly zealous set of masks that mistook heavy smoke plumes for clouds and/or inland water, and also an aerosol model developed for generic global aerosol conditions. 15Using Aerosol Robotic Network (AERONET) Version 3 sky inversions of local AERONET stations, we created a specific aerosol model for the extreme event. Thus, using this new less-absorbing aerosol model, cloud masking based on results of the MODIS cloud optical properties algorithm, and relaxed thresholds on both inland water tests and upper limits of the AOD retrieval we created a research algorithm, and applied it to 80 appropriate MODIS granules during the event.Collocating and comparing with AERONET AOD shows that the research algorithm doubles the number of MODIS 20 retrievals greater than 1.0, while also significantly improving agreement with AERONET. The final results show that the operational DT algorithm had missed approximately 0.22 of the regional mean AOD, but as much as AOD = 3.0 for individual 0.5° grid boxes. This amount of missing AOD can skew the perception of the severity of the event, affect estimates of regional aerosol forcing, and alter aerosol modeling and forecasting that assimilate MODIS aerosol data products. These results will influence the future development of the global DT aerosol algorithm. 25

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Wavelength dependence of the optical depth of biomass burning, urban, and desert dust aerosols

Cited by 1,988 publications

References 37 publications

On the twilight zone between clouds and aerosols

On the twilight zone between clouds and aerosols

Measurements of aerosol properties from aircraft, satellite and ground‐based remote sensing: a case‐study from the Dust and Biomass‐burning Experiment (DABEX)

Characterizing the 2015 Indonesia Fire Event Using Modified MODIS Aerosol Retrievals

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