Aerosols play a unique role in our atmosphere and can impact precipitation, reduce visibility, air quality, and human health. The direct and indirect radiative effects of aerosols on climate change remain a source of uncertainty in climate research. Dust outbreaks from the Sahara Desert prevail from the spring to the summer season each year. In spring, dust-laden air masses are transported within the marine boundary layer whereas they are often aloft from the source regions due to active convection in the summer. Understanding the impacts of dust on microphysical processes over the tropical North Atlantic Ocean under prevailing dust influence is critically important to study the global hydrological cycle.

The surface remote sensing and in-situ measurements of aerosol evolution and transport over ocean are especially difficult to obtain. The Trans-Atlantic Saharan Dust Aerosol and Ocean Science Expedition (AEROSE) employed a suite of aerosol instruments onboard the NOAA ship Ronald H. Brown during spring 2004, summer 2006 and summer 2007 provide a unique set of measurements to characterize aerosol properties and compositions near source regions and during transport across the tropical Atlantic Ocean. The Microtops sunphotometers (one of the instruments used in AEROSE) measure aerosol optical depth (AOD) at 340, 440, 675, and 870 nm, and water vapor from the 936 nm wavelength, which are in tandem with AERONET and MODIS-derived quantities over the visible-near infrared solar spectrum. We have compared the measurements of Microtops and AERONET sunphotometers with MODIS aerosol retrievals to study the validity of MODIS retrievals and feedbacks to MODIS algorithm in regard to sphericity and absorption. Secondly, we attempted to investigate any changes of aerosol optical properties during transport by following the outbreaks of dust plumes. In the late summer of 2006 (August 15-September 15), NASA conducted an aircraft campaign (known as NAMMA) using DC-8 with a number of aerosol sensors onboard to measure the vertical profiles of aerosol extinction, size, and single scattering albedo. These vertical distributions of aerosol properties together with the near surface measurements can be used to evaluate its impacts on microphysical processes.

We present a detailed analysis of aerosol optical properties including optical depth, effective particle size, single scattering albedo at and around AERONET sites (Cape Verde, Dahkar, Santa Cruz - Tenerife, Izana, and Puerto Rico) and along the tracks of the AEROSE as well as surface aerosol measurements at near the source versus those in the downwind. Using the validated satellite aerosol retrievals (with estimated errors) is an important step in developing more accurate Earth system models with the ability to characterize and predict the effects of dust on microphysical processes.