Cloud Fraction and Radar Reflectivity Statistics During EPIC2001

The first East Pacific Investigation of Climate Processes (EPIC) EPIC2001 field program was conducted during September and October of 2001. A major portion of this experiment was a coordinated set of atmospheric and oceanographic instruments deployed on the NOAA Research Vessel Ron Brown. Included in the suite of atmospheric sensors was a 35 GHz cloud radar which is identical to those being operated on a continuous basis at Department of Energy Cloud and Radiation Test-bed sites located in Alaska, Oklahoma, and the Tropical Western Pacific. This particular radar has developed a lengthy history of use in cloud and radiation studies over the previous 6-7 years including the development of a sophisticated suite of retrieval techniques for determining cloud optical depth, cloud water content, drizzle parameters, and hydrometeor sizes for both ice and liquid clouds. Retrievals of these cloud properties, as well as documentation of cloud thickness, cloud heights, and cloud fraction form the foundation of investigating interactions between clouds and surfaces fluxes and processes. In this study, a preliminary analysis is made of the cloud fractions and the cloud reflectivity statistics. These statistics are important as cloud fraction has been shown to be the controlling cloud parameter in determining SW and LW surface radiative cloud forcing (Fairall - this session), and radar reflectivity is the primary input for retrievals of cloud microphysical and optical properties that may have secondary effects on surface-cloud interactions. Statistics are calculated for different height bins, cloud types, and for regions above cloud base (determined by ceilometer) and below cloud base. The cloud fraction and radar reflectivity statistics are calculated separately for two regimes; the Eastern Pacific (95° W ) between the ITCZ and the equator, and in the marine stratocumulus region West of Peru. This study directly supports CLIVAR and EPIC2001 objectives of relating cloud microphysical properties of convective outflows to cloud radiative properties as well as improving bulk cloud-radiative parameterizations for marine stratus.