| dc.description.abstract | Abstract
The ground-based measurement of sea salt (SS) aerosol over the ocean requires the massive utilization of satellite-derived aerosol products. In this study, n-order spectral derivatives of multispectral aerosol optical depths (AODs) were examined to characterize SS and other aerosol types in terms of their spectral dependence related to their optical properties such as particle size distributions and complex refractive index (absorption and scattering). Based on theoretical simulations from the second simulation of a satellite signal in the solar spectrum (6S) model, wavelength-dependent spectral derivatives of SS were characterized along with other major types including mineral dust (DS), biomass burning (BB), and anthropogenic pollutant (AP). The approach of partitioning aerosol types with intrinsic values of particle size distribution (Angstrom Exponent, AE) and complex refractive index from normalized first- and second-order derivatives was applied to the datasets from a moderate resolution imaging spectroradiometer (MODIS) as well as by the ground-based aerosol robotic network (AERONET). The results after implementation from multiple sources of data indicated that the proposed approach could be highly effective for identifying and segregating abundant SS from DS, BB, and AP, across an ocean. Consequently, each aerosol’s shortwave direct radiative forcing and its efficiency could be further estimated in order to predict its impact on the climate system. The particle size distribution of SS was 0.08 ± 0.09, together with DS with AE 0.11 ± 0.13, BB with the particle size 2.34 ± 0.35), and AP with AE 1.18 ± 0.08. Smaller magnitudes of AE refer to coarse-mode dominant particles while large AE represents fine-mode dominating aerosols. The averaged radiative forcing (RF) exhibited that the SS had the smallest magnitude at TOA, −36 W/m2, while AP had the lowest magnitude at the BOA but the highest in the atmosphere, with −66.2 and 32.5 W/m2, respectively. SS generated the most efficient radiative cooling effects at TOA of all aerosol types as indicated by its steepest slope in the linear best fit between RF and AOD055 μm. AOD055 μm and normalized precipitable water vapor depicted positive correlation. At low (surface to 680 mb) and middle (680 – 400 mb) atmosphere, SS posed the most efficient aerosol, having the steepest slope of the line of best-fit, and generated more precipitable water vapor than the other 3 aerosol species. DS was the least efficient of all. The highest efficiency of SS in PW was also tailed by the relationship between AOD055 μm and cloud amount. SS exhibited the most effective aerosol species in enhancing cloud amount in low (< 4 km) and high (> 8 km) atmosphere, while AP demonstrated the most efficient in the middle atmosphere (4 – 8 km), followed by SS and DS.
Keywords: Aerosol Optical Depth, MODIS, CERES, aerosol types, sea salt, radiative forcing, precipitable water vapor. | en_US |