The main goal of the proposed project is to improve understanding of the mechanisms of spatio-temporal variability of aerosols in the tropics and their interactions with monsoon systems (American, South-East Asian, and West African monsoons), which are characterized by strong intraseasonal and interannual variability. The variability of aerosols retrieved from different satellites as well as their relationship to, and interaction with, different variables that characterize the dynamic and thermodynamic state of the tropical climate system will be objectively studied. The following research framework which combines a comprehensive and detailed data analysis as well as experimental numerical modeling will be employed: �?� Spatio-Temporal Aerosol Variability: Understand the main spatial and temporal modes of aerosol variability by analyzing TOMS, MODIS, POLDER and CALIPSO data. Determine the key mechanisms playing a role in the observed structure of the aerosol load annual cycle as well as in their interannual and intraseasonal variability. �?� Co-Variability of Aerosols and Tropical Climate: Perform a series of diagnostic analyses to study the relationship between atmospheric circulation, rainfall and atmospheric moisture with the aerosol load in different temporal and spatial scales. The statistical analyses will be designed to assess whether the amount of aerosol has an impact on the hydrological cycle and radiative budget in the tropics, as well as the role of tropical circulation in the spatio-temporal distribution of aerosols. Special attention will be given to the role of aerosols in the rainfall variability associated with the monsoon systems in Asia, Australia, Africa and the Americas given their role in the availability of water resources. �?� Real-time Aerosol Outlooks: Development of an online real-time analysis and probabilistic outlooks of aerosol load distribution based on the joint probability density functions between aerosols and different atmospheric variables and derived based historical information. We anticipate that we could provide daily outlooks for up to a week for the entire tropical belt (40?�S-40?�N) with a spatial resolution of 5?� by 5?�. �?� Experimental Numerical Modeling: Regional and tropical channel versions of the WRF model with dual moment cloud microphysics scheme will be used to interpret the results obtained from the diagnostic study under different atmospheric and aerosol scenarios. Different scenarios will include both realistic as well as reduced-degrees-of-freedom cases.