[1] Currently, the Moderate-resolution Imaging Spectroradiometers (MODIS) level II aerosol product (MOD04/MYD04) is the best aerosol optical depth product suitable for near-real-time aerosol data assimilation. However, a careful analysis of biases and error variances in MOD04/MYD04 aerosol optical depth product is necessary before implementing the MODIS aerosol product in aerosol forecasting applications. Using 1 year's worth of Sun photometer and MOD04/MYD04 aerosol optical depth (t) data over global oceans, we studied the major biases in MODIS aerosol over-ocean product due to wind speed, cloud contamination, and aerosol microphysical properties. For t less than 0.6, we found similar uncertainties in the mean MOD04/MYD04 t as suggested by the MODIS aerosol group, while biases are nonlinear for t larger than 0.6. We showed that uncertainties in MOD04/MYD04 data can be reduced, and the correlation between MODIS and Sun photometer t can be improved by reducing the systematic biases in MOD04/MYD04 data through empirical corrections and quality assurance procedures. By removing noise and outliers and ensuring that only the highest-quality data were included, we created a modified aerosol optical depth product that removes most massive outliers and ultimately reduced the absolute error (MODIS-Sun photometer) in MODIS t at 0.55 mm (t 0.55 ) by 10-20%. Averaged over 1 year's worth of Terra MODIS aerosol product over global oceans, we found a 12% reduction in MODIS t 0.55 with extremes of 30% over the southern midlatitudes and the North Pacific due to a reduction in cloud contamination. This modified aerosol optical depth product will be used operationally.Citation: Zhang, J., and J. S. Reid (2006), MODIS aerosol product analysis for data assimilation: Assessment of over-ocean level 2 aerosol optical thickness retrievals,

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[1] In this study, we present an aerosol data assimilation system destined for operational use at the Fleet Numerical Meteorological and Oceanographic Center (FNMOC). The system is an aerosol physics version of the Naval Research Laboratory (NRL) Atmospheric Variational Data Assimilation System (NAVDAS) that is already operational. The purpose of this new system, NAVDAS-Aerosol Optical Depth (NAVDAS-AOD) is to improve the NRL Aerosol Analysis and Prediction System (NAAPS)'s forecasting capability by assimilating observational data sources with NAAPS forecast fields. This will allow for not only improved aerosol forecasting but also for dramatically enhanced global scale research capabilities for the study of aerosol-meteorology interaction. NAVDAS-AOD assimilates a newly developed over-water Moderate-Resolution Imaging Spectroradiometers (MODIS) level 3 aerosol product with NAAPS. This paper is the second in a series which describes NRL's program to realistically monitor global aerosol distributions. Here we explain the reasons and procedures for constructing the over-water level 3 MODIS aerosol product, describe the theoretical basis for NAVDAS-AOD, and provide a thorough statistical error analysis for both the MODIS observations and the NAAPS model background fields that are critical to aerosol data assimilation. Using 5 months of analysis, our study shows that by carefully screening over-water satellite observations to ensure only the best quality data are used in the aerosol assimilation process, the NAVDAS-AOD can significantly improve the NAAPS global aerosol optical depth analysis as well as improve the aerosol forecast skill.

[1] Using spatially and temporally collocated MODerate Resolution Imaging Spectroradiometer (MODIS) products and data from seven AErosol RObotic NETwork (AERONET) sun-photometer sites, we explored the relationship between MODIS aerosol optical depth and cloud fraction over remote oceans that have been recently reported in the literature. We show that artifacts such as cloud contamination or adjacency effect contribute to the majority of the relationship in clean marine conditions. This cloud fraction effect could result in a 10 -20% overestimation in monthly mean aerosol optical depth or aerosol direct forcing values that are derived using MODIS aerosol products over cloud free oceans. It may also explain some of the high optical depth values derived in the midlatitude southern oceans. We also suggest that covariances of meteorological phenomenon such as wind or humidity in cloudy regions while logical might only account for a minor portion of the ensemble relationship. Citation: Zhang, J., J. S.Reid, and B. N. Holben (2005), An analysis of potential cloud artifacts in MODIS over ocean aerosol optical thickness products,