Deriving the effect of wind speed on clean marine aerosol optical properties using the A-Train satellites

Abstract

The relationship between "clean marine" aerosol optical properties and ocean surface wind speed is explored using remotely sensed data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the CALIPSO satellite and the Advanced Microwave Scanning Radiometer (AMSR-E) on board the AQUA satellite. Detailed data analyses are carried out over 15 regions selected to be representative of different areas of the global ocean for the time period from June 2006 to April 2011. Based on remotely sensed optical properties the CALIPSO algorithm is capable of discriminating "clean marine" aerosols from other types often present over the ocean (such as urban/industrial pollution, desert dust and biomass burning). The global mean optical depth of "clean marine" aerosol at 532 nm (AOD<sub>532</sub>) is found to be 0.052 ± 0.038 (mean plus or minus standard deviation). The mean layer integrated particulate depolarization ratio of marine aerosols is 0.02 ± 0.016. Integrated attenuated backscatter and color ratio of marine aerosols at 532 nm were found to be 0.003 ± 0.002 sr<sup>−1</sup> and 0.530 ± 0.149, respectively. A logistic regression between AOD<sub>532</sub> and 10-m surface wind speed (<i>U</i><sub>10</sub>) revealed three distinct regimes. For <i>U</i><sub>10</sub> ≤ 4 m s<sup>−1</sup> the mean CALIPSO-derived AOD<sub>532</sub> is found to be 0.02 ± 0.003 with little dependency on the surface wind speed. For 4 < <i>U</i><sub>10</sub> ≤ 12 m s<sup>−1</sup>, representing the dominant fraction of all available data, marine aerosol optical depth is linearly correlated with the surface wind speed values, with a slope of 0.006 s m<sup>−1</sup>. In this intermediate wind speed region, the AOD<sub>532</sub> vs. <i>U</i><sub>10</sub> regression slope derived here is comparable to previously reported values. At very high wind speed values (<i>U</i><sub>10</sub> > 18 m s<sup>−1</sup>), the AOD<sub>532</sub>-wind speed relationship showed a tendency toward leveling off, asymptotically approaching value of 0.15. The conclusions of this study regarding the aerosol extinction vs. wind speed relationship may have been influenced by the constant lidar ratio used for CALIPSO-derived AOD<sub>532</sub>. Nevertheless, active satellite sensor used in this study that allows separation of maritime wind induced component of AOD from the total AOD over the ocean could lead to improvements in optical properties of sea spray aerosols and their production mechanisms

Estimates of African Dust Deposition Along the Trans‐Atlantic Transit Using the Decadelong Record of Aerosol Measurements from CALIOP, MODIS, MISR, and IASI

“…Marine AOD in this study is assumed to increase with surface wind speed. Following an average of the relationships from Kiliyanpilakkil and Meskhidz () and Mulcahy et al (), we derive a global ocean mean AOD for marine aerosol of 0.066 at 0.55 μm, which agrees with the climatology based on the Aerosol Robotic Network (AERONET) observations (Kaufman et al, ; Smirnov et al, ).…”

The GAW‐PFR aerosol optical depth network: The 2008–2013 time series at Cape Point Station, South Africa

“…As oceans are a large source of coarse mode aerosols, a number of ground-based [Wilson and Forgan, 2002;Smirnov et al, 2003;Mulcahy et al, 2008] and satellite [Kiliyanpilakkil and Meskhidze, 2011, and references therein] studies have investigated the relationship of AOD with wind speed, finding that some form of linear or power law relationship exists. Observations from ground-based studies are particularly difficult to handle as data have to be carefully selected to treat the following: (1) the air mass origin and history, (2) the lifetime of coarse mode aerosols, and (3) the wind speed.…”

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

“…Satellite-derived and coast or island acquired AODs have been studied by Mulcahy et al (2008), Glantz et al (2009), Lehahn et al (2010), Huang et al (2010), O'Dowd et al (2010), Kiliyanpilakkil and Meskhidze (2011), Grandey et al (2011), Adames et al (2011), and Sayer et al (2012). Power-law and linear relationships between AOD and wind speed were established although sampling issues, uncertainties in retrieval algorithms, and/or influence of the chosen island locations gave an indication that the problem is far from being solved and there is not yet consensus.…”