0CLAPMBL

Azores: Extension to Clouds, Aerosol and Precipitation in the Marine Boundary Layer (CAP-MBL)

1 January 2010 - 6 January 2011

Lead Scientist: Robert Wood

Observatory: AMF , GRW

The response of marine low clouds to changes in atmospheric greenhouse gases and aerosols is a major source of uncertainty that thwarts accurate prediction of future climate change. Low clouds are poorly simulated in climate models, chiefly because their structural and optical properties are strongly dependent upon interactions between aerosol/cloud microphysics and dynamics that are unresolved in such models. These interactions intricately involve the formation of precipitation and its effect upon cloud dynamics, turbulence, and entrainment. However, we still do not understand many of the key physical links between aerosol and cloud microphysical properties, nor do we have sufficient observations to accurately quantify the multivariate sensitivity of precipitation to cloud microphysical and macrophysical properties. Such closure studies are essential for the evaluation of both climate and process-based numerical models. To be useful, closure studies require statistically robust and physically accurate observational datasets obtained over long periods of time. Such datasets are very rare in the subtropical marine boundary layer where climate models show the greatest discrepancy in cloud responses. The 2009 deployment of the ARM Mobile Facility (AMF) on Graciosa Island (The Azores, 28°W 39°N) will be extended for an additional 9-12 months (from Dec 2009 to Fall 2010) to continue to study dynamical and microphysical processes controlling the radiative properties (thickness, coverage, microphysics, and optical properties) of marine boundary layer (MBL) clouds over the remote Northeast Atlantic Ocean (NEA). We believe that the extended dataset from the AMF will provide significantly greater statistical reliability of the multivariate relationships between aerosol and cloud microphysical/macrophysical properties required for evaluation of climate and process models. The extended AMF deployment will also provide an unprecedented opportunity to study the seasonal cycle, to test the ACRF’s planned scanning radar capability, and to assess the feasibility of the site for a possible permanent ACRF site. We will also conduct an ARM Aerial Facility (AAF) deployment for a month-long period during Jun-Aug 2010 which will (a) provide important in-situ data for the evaluation of the AMF remote sensing retrievals; (b) provide critical data for closure studies. The AAF measurements will maximize the potential of the ground based remote sensing capability of the AMF. The following four types of closure studies will be performed with the combination of the AMF and the AAF: (a) cloud microphysical closure: sensitivity of cloud microphysical properties to aerosol chemical/physical properties and cloud dynamics; (b) drizzle closure: relationships between precipitation and cloud macrophysical and microphysical properties; (c) entrainment closure: sensitivity of entrainment to cloud and boundary layer structure and dynamics; (d) radiative closure: sensitivity of the cloud optical depth to macrophysical and microphysical cloud properties. These studies will be addressed with the AMF as a central pillar in a research structure that will include multi-scale modeling work as detailed in the proposal for the 2009 AMF deployment. Synthesized long term data from the AMF will be used to initialize, constrain, and validate numerical models including large eddy simulation, single column, and regional and global atmospheric models as an important component of the proposed work.