1. Probing continental boundary layer clouds using first-time, extended-term aircraft observations: Low-level boundary layer clouds include stratus, stratocumulus, and fair- weather cumulus that are ubiquitous over many parts of the globe and strongly influence the Earth’s radiative energy balance. However, our understanding of these clouds is insufficient to solve pressing scientific problems. The need for a better understanding of boundary layer clouds requires quality in-situ data that can be applied to process studies, fine-scale model evaluation, and the refinement of retrieval algorithms. RACORO, a first-of-a-kind extended-term cloud aircraft campaign, was conducted to obtain a statistical characterization of continental, boundary-layer, liquid-water clouds. The 5-month campaign provided an in-situ dataset that characterizes a wide range of continental, boundary layer, cloud and aerosol property states for climate studies. These data include observations of clouds that are below the detection limit of common remote sensing techniques, and also of aerosol and atmospheric state properties that affect cloud development but are difficult to remotely sense. Proximity of the campaign to the ARM Southern Great Plains site’s extensive complement of surface measurements provides data that supports analyses and modeling studies of the aircraft data. Reference: Vogelmann, A. M., G. M. McFarquhar, J. A. Ogren, D. D. Turner, J. M. Comstock, G. Feingold, C. N. Long, H. H. Jonsson, A. Bucholtz, D. R. Collins, G. S. Diskin, H. Gerber, R. P. Lawson, R. K. Woods, E. Andrews, H.-J. Yang, J. C. Chiu, D. Hartsock, J. M. Hubbe, C. Lo, A. Marshak, J. W. Monroe, S. A. McFarlane, B. Schmid, J. M. Tomlinson, and T. Toto, 2012: “RACORO Extended-Term, Aircraft Observations of Boundary-Layer Clouds,” Bull. Amer. Meteor. Soc, 93, 861–878.

2. Cumulative Frequency distribution Normalized Frequency distribution Average Liquid-Water Content (LWC) [g m -3 ] Frequency Distribution Motivation ● A better understanding of boundary-layer clouds requires in-situ data for process studies, fine-scale model evaluation, and refinement of retrieval algorithms. Approach ● The RACORO* aircraft campaign operated for an extended period over the Southern Great Plains ARM site with a comprehensive payload that measured cloud microphysics, solar and thermal radiation, physical aerosol properties, & atmospheric state parameters. Result ● A 5-month campaign, from 22 January to 30 June 2009, that involved 260 flight hrs and provided the first extended-term, in-situ aircraft dataset of a wide range of continental boundary layer clouds and aerosol properties for climate studies. Probing Continental Boundary Layer Clouds Using First-Time, Extended-Term Aircraft Observations A. M. Vogelmann, G. M. McFarquhar, J. A. Ogren, D. D. Turner, J. M. Comstock, G. Feingold, C. N. Long, H. H. Jonsson, A. Bucholtz, D. R. Collins, G. S. Diskin, H. Gerber, R. P. Lawson, R. K. Woods, E. Andrews, H.-J. Yang, J. C. Chiu, D. Hartsock, J. M. Hubbe, C. Lo, A. Marshak, J. W. Monroe, S. A. McFarlane, B. Schmid, J. M. Tomlinson, and T. Toto, 2012: “RACORO Extended-Term, Aircraft Observations of Boundary-Layer Clouds,” Bull. Amer. Meteor. Soc, 93, 861–878. Frequency distributions of all aircraft LWCs during RACORO. Cloud thickness (dashed lines) indicate the LWCs that pertain to a liquid-water path (LWP) of 30 g m ‑ 2, which is the uncertainty of commonly used 2-channel (23 and 31 GHz) microwave radiometers (MWRs). The distribution to the left of a line is below the MWR LWP uncertainty. RACORO clouds were typically between 200 and 500 m thick so 35 to 70% of these clouds could be below the 30 g m -2 uncertainty limit. *RACORO stands for Routine ARM Aerial Facility (AAF) Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations Cloud Thickness for LWP=30 g m -2 1000m 500 m 200 m