Aerosols in the marine boundary layer at the Azores AMF

The ARM Mobile Facility (AMF) deployment at Graciosa Island in the Azores during May 2009 - December 2010 provides continuous meteorological and aerosol measurements of the marine boundary layer (MBL) in the North Atlantic Ocean. These data are central to the CAP-MBL (Clouds, Aerosols and Precipitation in the Marine Boundary Layer) project which aims to better understand cloud-aerosol-precipitation interactions in the cloudy MBL. Here we report on some preliminary results from CAP-MBL.

The Azores region hosts a variety of cloud types in the MBL including stratocumulus, trade cumulus, and transitional clouds. Back trajectories from the MBL at Graciosa imply diverse geographic sources of aerosol including anthropogenically modified air from Europe and northern North America, and relatively pristine air from the Arctic.

We find that ground-based sun-photometer measurements of AOD at Graciosa agree reasonably well with daily MODIS AOD measurements over a four month period starting in July 2009. The 10th and 90th percentile photometer AOD at 500nm during this period was 0.09 and 0.23, respectively. We also compare these column measurements of AOD with measured near-surface CCN concentrations in order to evaluate the usefulness of satellite AOD as a proxy for CCN concentration. Cloud effective radius from satellite is also compared to measured CCN concentrations.

We also compare the relationship of precipitation to liquid water path under varying aerosol concentrations. We may also present a preliminary comparison of NCAR and GFDL atmospheric climate model simulations that include new aerosol, microphysical, and cloud parameterizations with measurements at the AMF.