A study of 15-year aerosol optical thickness and direct shortwave aerosol radiative effect trends using MODIS, MISR, CALIOP and CERES

Alfaro-Contreras, R.; Zhang, Jianglong; Reid, Jeffrey S.; Christopher, Sundar A.

doi:10.5194/acp-17-13849-2017

Cited by 40 publications

(36 citation statements)

References 42 publications

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“…While there is no significant overall trend to this offset, there are short periods of increase and decrease, and its variability appears to increase. A similar pattern was observed by Alfaro-Contreras et al (2017). Over ocean, the offset averages +0.018, which is also ~12% of the MYD04 global mean.…”

supporting

confidence: 78%

“…In particular, the Moderate-resolution Imaging Spectroradiometer (MODIS) instruments onboard the polar orbiting satellites Terra (since 2000) and Aqua (since 2002) provide state-of-art spatial resolution and near-daily retrievals of AOD and other aerosol parameters on a global scale. The length of the aerosol records has prompted studies of the trends in global and regional aerosol loading, and subsequently, estimate changes in aerosol forcing or radiative effects 20 (Zhang and Reid, 2010;Hsu et al, 2012;Chin et al, 2014;Alfaro-Contreras et al, 2017;Colarco et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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Response to Anonymous Reviewer #1 Comments

Levy¹

2018

Preprint

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Long-term measurements of global aerosol loading and optical properties are essential for assessing climate-related questions. Using observations of spectral reflectance and radiance, the dark-target (DT) aerosol retrieval algorithm is applied to Moderate-resolution Imaging Spectroradiometer sensors on both Terra (MODIS-T) and Aqua (MODIS-A) satellites, deriving products (known as MOD04 and MYD04, respectively) of global aerosol optical depth (AOD at 0.55 µm) over both land and 15 ocean, and Angstrom Exponent (AE derived from 0.55 and 0.86 µm) over ocean. Here, we analyse the overlapping time series (since mid-2002) of the Collection 6 (C6) aerosol products. Global monthly mean AOD from MOD04 (Terra with morning overpass) is consistently higher than MYD04 (Aqua with afternoon overpass) by ~13% (~0.02 over land and ~0.015 over ocean), and this offset (MOD04 -MYD04), has seasonal as well as long-term variability. Focusing on 2008, and deriving yearly gridded mean AOD and AE, we find that over ocean, the MOD04 (morning) AOD is higher and the AE is lower. Over land, there is more 20 variability, but only biomass-burning regions tend to have AOD lower for MOD04. Using simulated aerosol fields from the Goddard Earth Observing System (GEOS-5) Earth system model, and sampling separately (in time and space) along each MODIS-observed swath during 2008, the magnitudes of morning versus afternoon offsets of AOD and AE are smaller than those in the C6 products. Since the differences are not easily attributed to either aerosol diurnal cycles or sampling issues, we test additional corrections to the input reflectance data. The first, known as C6+, corrects for long-term changes to each sensors' 25 polarization sensitivity, response-versus-scan angle, and to cross-calibration from MODIS-T to MODIS-A. A second convolves the de-trending and cross-calibration into scaling factors. Each method was applied upstream of the aerosol retrieval, using 2008 data. While both methods reduced the overall AOD offset over land from 0.02 to 0.01, neither significantly reduced the AOD offset over ocean. The overall negative AE offset was reduced. A Collection (C6.1) of all MODIS-atmosphere products was released, but we expect that the C6.1 aerosol products will maintain similar overall AOD and AE offsets. We conclude that: a) 30 users should not interpret global differences between Terra and Aqua aerosol products as representing a true diurnal signal in the aerosol. b) Because the MODIS-A product appears to have overall smaller bias compared to ground-truth, it may be more suitable for some applications, however c) since the AOD offset is only ~0.02 and within noise level for single retrievals, both MODIS products may be adequate for most applications.

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supporting

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Response to Anonymous Reviewer #1 Comments

Levy¹

2018

Preprint

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“…For example, Zhang et al (2017) analyzed MODIS data over the northwestern Pacific Ocean and found that AOD has undergone a shift from an increasing trend over 2000-2007 to a decreasing trend over 2007-2015. Alfaro-Contreras et al (2017) analyzed several satellite retrievals of AOD for total aerosol and found no consistent trend in coastal China (−0.035, +0.001, −0.010 per decade for MODIS Aqua, MODIS Terra, and MISR, respectively). Sogacheva et al (2018) combined AOD data from the Along-Track Scanning Radiometer (ATSR) and MODIS and found that AOD across China increased significantly from 1995 to 2006 but decreased gradually between 2011 and 2017, which reflects the increased emissions due to rapid economic development and the decreased emissions due to effective emission control regulations.…”

Section: Non-monotonic Trends Of τ C In East Asian Outflowsmentioning

confidence: 99%

Interannual variability and trends of combustion aerosol and dust in major continental outflows revealed by MODIS retrievals and CAM5 simulations during 2003–2017

Yang

Wang

et al. 2020

Atmos. Chem. Phys.

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Abstract. Emissions and long-range transport of mineral dust and combustion-related aerosol from burning fossil fuels and biomass vary from year to year, driven by the evolution of the economy and changes in meteorological conditions and environmental regulations. This study offers both satellite and model perspectives on the interannual variability and possible trends of combustion aerosol and dust in major continental outflow regions over the past 15 years (2003–2017). The decade-long record of aerosol optical depth (AOD, denoted as τ), separately for combustion aerosol (τc) and dust (τd), over global oceans is derived from the Collection 6 aerosol products of the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard both Terra and Aqua. These MODIS Aqua datasets, complemented by aerosol source-tagged simulations using the Community Atmospheric Model version 5 (CAM5), are then analyzed to understand the interannual variability and potential trends of τc and τd in the major continental outflows. Both MODIS and CAM5 consistently yield a similar decreasing trend of −0.017 to −0.020 per decade for τc over the North Atlantic Ocean and the Mediterranean Sea that is attributable to reduced emissions from North America and Europe, respectively. On the contrary, both MODIS and CAM5 display an increasing trend of +0.017 to +0.036 per decade for τc over the tropical Indian Ocean, the Bay of Bengal, and the Arabian Sea, which reflects the influence of increased anthropogenic emissions from South Asia and the Middle East in the last 2 decades. Over the northwestern Pacific Ocean, which is often affected by East Asian emissions of pollution and dust, the MODIS retrievals show a decreasing trend of −0.021 per decade for τc and −0.012 per decade for τd, which is, however, not reproduced by the CAM5 model. In other outflow regions strongly influenced by biomass burning smoke or dust, both MODIS retrievals and CAM5 simulations show no statistically significant trends; the MODIS-observed interannual variability is usually larger than that of the CAM5 simulation.

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“…The length of the aerosol records has 20 prompted studies of the trends in global and regional aerosol loading, and subsequently, estimate changes in aerosol forcing or radiative effects (Zhang and Reid, 2010;Hsu et al, 2012;Chin et al, 2014;Alfaro-Contreras et al, 2017;Colarco et al, 2014).…”

mentioning

confidence: 99%

Exploring systematic offsets between aerosol products from the two MODIS sensors

Levy¹,

Mattoo²,

Sawyer³

et al. 2018

Preprint

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Abstract. Long-term measurements of global aerosol loading and optical properties are essential for assessing climate-related questions. Using observations of spectral reflectance and radiance, the dark-target (DT) aerosol retrieval algorithm has been applied to Moderate-resolution Imaging Spectroradiometer sensors on both Terra (MODIS-T) and Aqua (MODIS-A) satellites, deriving products (known as MOD04 and MYD04, respectively) of global aerosol optical depth (AOD at 0.55 µm) over both 15 land and ocean, and Angstrom Exponent (AE derived from 0.55 and 0.86 µm) over ocean. Here, we analyse the overlapping time series (since mid-2002) of the Collection 6 (C6) aerosol products. Global monthly mean AOD from MOD04 (Terra with morning overpass) is consistently higher than MYD04 (Aqua with afternoon overpass) by ~13% (~0.02 over land and ~0.015 over ocean), and this offset (MOD04 -MYD04), has seasonal as well as long-term variability. Focusing on 2008, and deriving yearly gridded mean AOD and AE, we find that over ocean, the MOD04 (morning) AOD is higher and the AE is lower. Over 20 land, there is more variability, but only biomass-burning regions tend to have AOD lower for MOD04. Using simulated aerosol fields from the Goddard Earth Observing System (GEOS-5) Earth system model, and sampling separately (in time and space) along each MODIS-observed swath during 2008, the magnitudes of morning versus afternoon offsets of AOD and AE are smaller than those in the C6 products. Since the differences are not easily attributed to either aerosol diurnal cycles or sampling issues, we test additional corrections to the input reflectance data. The first, known as C6+, corrects for long-term changes to 25 each sensors' polarization sensitivity, response-versus-scan angle, and to cross-calibration from MODIS-T to MODIS-A. A second convolves the de-trending and cross-calibration into scaling factors. Each method was applied upstream of the aerosol retrieval, using 2008 data. While both methods reduced the overall AOD offset over land from 0.02 to 0.01, neither significantly reduced the AOD offset over ocean. The overall negative AE offset was reduced. A Collection (C6.1) of all MODIS-atmosphere products was released, but we expect that the C6.1 aerosol products will maintain similar overall AOD and 30 AE offsets. We conclude that: a) users should not interpret global differences between Terra and Aqua aerosol products as representing a true diurnal signal in the aerosol. b) Because the MODIS-A product appears to have overall smaller bias compared to ground-truth, it may be more suitable for some applications, however c) since the AOD offset is only ~0.02 and within noise level for single retrievals, both MODIS products may be adequate for most applications.Atmos. Meas. Tech. Discuss., https://doi

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A study of 15-year aerosol optical thickness and direct shortwave aerosol radiative effect trends using MODIS, MISR, CALIOP and CERES

Cited by 40 publications

References 42 publications

Response to Anonymous Reviewer #1 Comments

Response to Anonymous Reviewer #1 Comments

Interannual variability and trends of combustion aerosol and dust in major continental outflows revealed by MODIS retrievals and CAM5 simulations during 2003–2017

Exploring systematic offsets between aerosol products from the two MODIS sensors

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