To better understand the influence of clouds on radiative transfer, scientists need better information about not only the specific cloud microphysics, but also the state of the surrounding atmosphere.

Despite extensive instrumentation deployed at the ACRF sites, some quantities of interest remain either impractical or impossible to measure directly or routinely. For this reason, some ARM Program science needs are met through the analysis and processing of existing data products into “value-added” products, or VAPs. Earlier this year, the Merged Sounding VAP was used to define atmospheric state at 1-minute time intervals for one month at each of the ACRF permanent sites, meeting the 2006 first quarter performance metric set forth by the ARM Program. Similarly, the Microbase VAP was produced to refine a 1-year continuous time series of cloud microphysical properties for each of the fixed ARM sites, thereby meeting the third quarter performance metric.

The Merged Sounding VAP combines data from surface sensors and weather balloons launched at ACRF sites with information about the state of the atmosphere from operational weather observing networks to produce a best estimate of the vertical profiles of the temperature, water vapor content, barometric pressure and horizontal winds above each site. For the Microbase VAP, a combination of recently developed algorithms was used for interpreting radar reflectivity profiles, lidar backscatter profiles, and microwave brightness temperatures into the context of the underlying cloud microphysical structure.

The product of this analysis—a continuous baseline microphysical retrieval (or “microbase”)—includes vertical profiles of the liquid/ice water content, liquid/ice cloud particle effective radius and cloud fraction, at 20-minute time intervals and over 230 vertical levels. The Microbase (VAP) has been applied to the ACRF Southern Great Plains site for March 2000 - February 2001; the North Slope of Alaska site for January 2004 - December 2004; and the Tropical Western Pacific site at Manus Island for November 2003 - October 2004.

In combination, the Merged Sounding and Microbase VAPs have been used as input to the broadband heating rate profile (BBHRP) for selected time periods at the ACRF permanent sites. In 2007, both Merged Sounding and Microbase VAP results are scheduled to be released to the Data Archive as permanent ARM VAPs, beginning with data from the Southern Great Plains site.