scholarly journals Wind Speed Influences on Marine Aerosol Optical Depth

2010 ◽  
Vol 2010 ◽  
pp. 1-7 ◽  
Author(s):  
Colin O'Dowd ◽  
Claire Scannell ◽  
Jane Mulcahy ◽  
S. Gerard Jennings
Keyword(s):  
Wind Speed ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Power Law ◽  
Anthropogenic Pollution ◽  
Open Ocean ◽  
Marine Aerosol ◽  
Wind Speeds ◽  
General Power ◽  
Relationship Of

The Mulcahy (Mulcahy et al., 2008) power-law parameterization, derived at the coastal Atlantic station Mace Head, between clean marine aerosol optical depth (AOD) and wind speed is compared to open ocean MODIS-derived AOD versus wind speed. The reported AOD versus wind speed (U) was a function of ∼U2. The open ocean MODIS-derived AOD at 550 nm and 860 nm wavelengths, while in good agreement with the general magnitude of the Mulcahy parameterization, follows a power-law with the exponent ranging from 0.72 to 2.47 for a wind speed range of 2–18 m s−1. For the four cases examined, some MODIS cases underestimated AOD while other cases overestimated AOD relative to the Mulcahy scheme. Overall, the results from MODIS support the general power-law relationship of Mulcahy, although some linear cases were also encountered in the MODIS dataset. Deviations also arise between MODIS and Mulcahy at higher wind speeds (>15 m s−1), where MODIS-derived AOD returns lower values as compared to Mulcahy. The results also support the suggestion than wind generated sea spray, under moderately high winds, can rival anthropogenic pollution plumes advecting out into marine environments with wind driven AOD contributing to AOD values approaching 0.3.

scholarly journals Estimating the maritime component of aerosol optical depth and its dependency on surface wind speed using satellite data

2010 ◽  
Vol 10 (14) ◽  
pp. 6711-6720 ◽  
Author(s):  
Y. Lehahn ◽  
I. Koren ◽  
E. Boss ◽  
Y. Ben-Ami ◽  
O. Altaratz
Keyword(s):  
Wind Speed ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Time Scale ◽  
Time Lag ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Time Frame ◽  
Marine Aerosol ◽  
Wind Intensity

Abstract. Six years (2003–2008) of satellite measurements of aerosol parameters from the Moderate Resolution Imaging Spectroradiometer (MODIS) and surface wind speeds from Quick Scatterometer (QuikSCAT), the Advanced Microwave Scanning Radiometer (AMSR-E), and the Special Sensor Microwave Imager (SSM/I), are used to provide a comprehensive perspective on the link between surface wind speed and marine aerosol optical depth over tropical and subtropical oceanic regions. A systematic comparison between the satellite derived fields in these regions allows to: (i) separate the relative contribution of wind-induced marine aerosol to the aerosol optical depth; (ii) extract an empirical linear equation linking coarse marine aerosol optical depth and wind intensity; and (iii) identify a time scale for correlating marine aerosol optical depth and surface wind speed. The contribution of wind induced marine aerosol to aerosol optical depth is found to be dominated by the coarse mode elements. When wind intensity exceeds 4 m/s, coarse marine aerosol optical depth is linearly correlated with the surface wind speed, with a remarkably consistent slope of 0.009±0.002 s/m. A detailed time scale analysis shows that the linear correlation between the fields is well kept within a 12 h time frame, while sharply decreasing when the time lag between measurements is longer. The background aerosol optical depth, associated with aerosols that are not produced in-situ through wind driven processes, can be used for estimating the contributions of terrestrial and biogenic marine aerosol to over-ocean satellite retrievals of aerosol optical depth.

scholarly journals Accuracy assessment of Aqua-MODIS aerosol optical depth over coastal regions: importance of quality flag and sea surface wind speed

2012 ◽  
Vol 5 (4) ◽  
pp. 5205-5243 ◽  
Author(s):  
J. C. Anderson ◽  
J. Wang ◽  
J. Zeng ◽  
M. Petrenko ◽  
G. G. Leptoukh ◽  
...  
Keyword(s):  
Wind Speed ◽  
Density Function ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Open Ocean ◽  
Sea Surface ◽  
Coastal Regions ◽  
Modis Aod

Abstract. Coastal regions around the globe are a major source for anthropogenic aerosols in the atmosphere, but the underlying surface characteristics are not favorable for the Moderate Resolution Imaging Spectroradiometer (MODIS) algorithms designed for retrieval of aerosols over dark land or open-ocean surfaces. Using data collected from 62 coastal stations worldwide from the Aerosol Robotic Network (AERONET) from ~ 2002–2010, accuracy assessments are made for coastal aerosol optical depth (AOD) retrieved from MODIS aboard Aqua satellite. It is found that coastal AODs (at 550 nm) characterized respectively by the MODIS Dark Land (hereafter Land) surface algorithm, the Open-Ocean (hereafter Ocean) algorithm, and AERONET all exhibit a log-normal distribution. After filtering by quality flags, the MODIS AODs respectively retrieved from the Land and Ocean algorithms are highly correlated with AERONET (with R2 &amp;approx; 0.8), but only the Land algorithm AODs fall within the expected error envelope greater than 66% of the time. Furthermore, the MODIS AODs from the Land algorithm, Ocean algorithm, and combined Land_and_Ocean product show statistically significant discrepancies from their respective counterparts from AERONET in terms of mean, probability density function, and cumulative density function, which suggest a need for future improvement in retrieval algorithms. Without filtering with quality flag, the MODIS Land_and_Ocean AOD dataset can be degraded by 30–50% in terms of mean bias. Overall, the MODIS Ocean algorithm overestimates the AERONET coastal AOD by 0.021 for AOD < 0.25 and underestimates it by 0.029 for AOD > 0.25. This dichotomy is shown to be related to the ocean surface wind speed and cloud contamination effects on the satellite aerosol retrieval. The Modern Era Retrospective-Analysis for Research and Applications (MERRA) reveals that wind speeds over the global coastal region (with a mean and median value of 2.94 m s−1 and 2.66 m s−1, respectively) are often slower than 6 m s−1 assumed in the MODIS Ocean algorithm. As a result of high correlation (R2 > 0.98) between the bias in binned MODIS AOD and the corresponding binned wind speed over the coastal sea surface, an empirical scheme for correcting the bias of AOD retrieved from the MODIS Ocean algorithm is formulated and is shown to be effective over the majority of the coastal AERONET stations, and hence can be used in future analysis of AOD trend and MODIS AOD data assimilation.

scholarly journals Estimating the maritime component of aerosol optical depth and its dependency on surface wind speed using MODIS and QuikSCAT data

2010 ◽  
Vol 10 (1) ◽  
pp. 1983-2003 ◽  
Author(s):  
Y. Lehahn ◽  
I. Koren ◽  
E. Boss ◽  
Y. Ben-Ami ◽  
O. Altaratz
Keyword(s):  
Wind Speed ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Surface Wind ◽  
World Ocean ◽  
Surface Wind Speed ◽  
Marine Aerosol ◽  
Coarse Mode ◽  
Wind Intensity ◽  
Threshold Wind Speed

Abstract. Seven years (2002–2008) of satellite measurements from SeaWinds aboard Quick Scatterometer (QuikSCAT) and Moderate Resolution Imaging Spectroradiometer (MODIS) aboard Terra are used for providing a global view on the link between surface wind speed and marine aerosol optical depth. This study shows that away form the continents the correlation time between the surface winds and the marine aerosol exceeds 4 h and therefore the two measurements can be linked. A systematic comparison between the satellite derived fields at different locations over the World Ocean allows to: (i) separate the relative contribution of wind-induced marine aerosol to the aerosol optical depth (ii) identify a threshold wind speed for triggering maritime contribution to aerosol optical depth; and (iii) extract an empirical linear equation linking marine aerosol optical depth and wind intensity. Wind induced marine aerosol contribution to aerosol optical depth is found to be dominated by the coarse mode elements. The threshold wind speed for triggering emission of coarse maritime aerosol is remarkably consistent with an average value of 4.1±0.1 m/s. When wind intensity exceeds the threshold value, coarse mode marine aerosol optical depth is linearly correlated to the surface wind speed, with a consistent slope of 0.0082±0.0004 s/m. The background aerosol optical depth, associated with aerosols that are not produced in-situ through wind driven processes, shows relatively large seasonal and geographical variability, and can be used for estimating the contribution of terrestrial aerosols to the aerosol optical depth over the ocean.

Height Extrapolation of Wind Data

1985 ◽  
Vol 107 (1) ◽  
pp. 10-14 ◽  
Author(s):  
A. S. Mikhail
Keyword(s):  
Wind Speed ◽  
Power Law ◽  
Wind Data ◽  
Power Law Model ◽  
Short Term ◽  
Shape Factors ◽  
Wind Speeds ◽  
Average Wind ◽  
Modified Power Law

Various models that are used for height extrapolation of short and long-term averaged wind speeds are discussed. Hourly averaged data from three tall meteorological towers (the NOAA Erie Tower in Colorado, the Battelle Goodnoe Hills Tower in Washington, and the WKY-TV Tower in Oklahoma), together with data from 17 candidate sites (selected for possible installation of large WECS), were used to analyze the variability of short-term average wind shear with atmospheric and surface parameters and the variability of the long-term Weibull distribution parameter with height. The exponents of a power-law model, fit to the wind speed profiles at the three meteorological towers, showed the same variability with anemometer level wind speed, stability, and surface roughness as the similarity law model. Of the four models representing short-term wind data extrapolation with height (1/7 power law, logarithmic law, power law, and modified power law), the modified power law gives the minimum rms for all candidate sites for short-term average wind speeds and the mean cube of the speed. The modified power-law model was also able to predict the upper-level scale factor for the WKY-TV and Goodnoe Hills Tower data with greater accuracy. All models were not successful in extrapolation of the Weibull shape factors.

scholarly journals Technical note: Absorption aerosol optical depth components from AERONET observations of mixed dust plumes

2018 ◽  
Author(s):  
Sung-Kyun Shin ◽  
Matthias Tesche ◽  
Detlef Müller ◽  
Youngmin Noh
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Mineral Dust ◽  
Anthropogenic Pollution ◽  
Technical Note ◽  
Dust Aerosol ◽  
Anthropogenic Sources ◽  
Absorbing Aerosols ◽  
And Inversion ◽  
Aerosol Plume

Abstract. Absorption aerosol optical depth (AAOD) as obtained from sun/sky photometer measurements provides a measure of the light-absorbing properties of the columnar aerosol loading. However, it is not an unambiguous, aerosol-type specific parameter, particularly if several types of absorbing aerosols, for instance black carbon (BC) and mineral dust, are present in a mixed aerosol plume. The contribution of mineral dust to total aerosol light-absorption is particularly important at UV wavelengths. In this study we refine a lidar-based technique for the separation of dust and non-dust aerosol types for the use with Aerosol Robotic Network (AERONET) direct sun and inversion products. We extend the methodology to retrieve AAOD related to non-dust aerosol (AAODnd) and BC (AAODBC). We test the method at selected AERONET sites that are frequently affected by aerosol plumes that contain a mixture of Saharan or Asian mineral dust and biomass-burning smoke or anthropogenic pollution, respectively. We find that aerosol optical depth (AOD) related to mineral dust as obtained with our methodology is frequently smaller than coarse-mode AOD. This suggests that the latter is not an ideal proxy for estimating the contribution of mineral dust to mixed dust plumes. We present the results of the AAODBC retrieval for the selected AERONET sites and compare them to coincident values provided in the Copernicus Atmospheric Monitoring System aerosol re-analysis. We find that modelled and AERONET AAODBC are most consistent for Asian sites or at Saharan sites with strong local anthropogenic sources.

scholarly journals Effect of wind speed on aerosol optical depth over remote oceans, based on data from the Maritime Aerosol Network

2012 ◽  
Vol 5 (2) ◽  
pp. 377-388 ◽  
Author(s):  
A. Smirnov ◽  
A. M. Sayer ◽  
B. N. Holben ◽  
N. C. Hsu ◽  
S. M. Sakerin ◽  
...  
Keyword(s):  
Wind Speed ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Surface Wind ◽  
Correlation Coefficients ◽  
Surface Wind Speed ◽  
Near Surface ◽  
Strong Winds ◽  
The Relationship ◽  
Good Agreement

Abstract. The Maritime Aerosol Network (MAN) has been collecting data over the oceans since November 2006. The MAN archive provides a valuable resource for aerosol studies in maritime environments. In the current paper we investigate correlations between ship-borne aerosol optical depth (AOD) and near-surface wind speed, either measured (onboard or from satellite) or modeled (NCEP). According to our analysis, wind speed influences columnar aerosol optical depth, although the slope of the linear regression between AOD and wind speed is not steep (~0.004–0.005), even for strong winds over 10 m s−1. The relationships show significant scatter (correlation coefficients typically in the range 0.3–0.5); the majority of this scatter can be explained by the uncertainty on the input data. The various wind speed sources considered yield similar patterns. Results are in good agreement with the majority of previously published relationships between surface wind speed and ship-based or satellite-based AOD measurements. The basic relationships are similar for all the wind speed sources considered; however, the gradient of the relationship varies by around a factor of two depending on the wind data used.

scholarly journals Long-Term Variation of Black Carbon Absorption Aerosol Optical Depth from AERONET Data over East Asia

2020 ◽  
Vol 12 (21) ◽  
pp. 3551
Author(s):  
Naghmeh Dehkhoda ◽  
Youngmin Noh ◽  
Sohee Joo
Keyword(s):  
East Asia ◽  
Black Carbon ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Anthropogenic Pollution ◽  
Single Scattering ◽  
Chinese Government ◽  
Rapid Reduction ◽  
Term Data

Absorption aerosol optical depth induced by black carbon (AAODBC) was retrieved using the depolarization ratio and single scattering albedo provided by the Aerosol Robotic Network (AERONET) inversion products over East Asia. Our analysis considered AERONET data from six sites in East Asia that are mostly affected by anthropogenic pollution, black carbon (BC) emissions, and natural mineral dust, during the period 2001–2018. We identified a rapid reduction in total aerosol optical depth (AODT) of −0.0106 yr−1 over Beijing, whereas no considerable trend was observed at the Korean and Japanese sites. The long-term data for AAODBC showed decreasing trends at all sites. We conclude that successful emission control policies were the major underlying driver of AODT and AAODBC reductions over East Asia, particularly in China, during the study period. Values of the AAODBC/AODT ratio revealed that, although these policies were successful, the Chinese government needs to undertake stricter measures toward reducing BC emissions. We found that AAODBC follows seasonal trends, peaking in the colder months. This suggests that in East Asia, particularly in China, domestic coal burning is still of concern.

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