Shaocheng Xie, Renata McCoy, and Stephen Klein Lawrence Livermore National Laboratory

1. Statistical Characteristics of Clouds Observed at the ARM SGP, NSA, and TWP sites Shaocheng Xie, Renata McCoy, and Stephen Klein Lawrence Livermore National Laboratory ____________________________________________________________________________________________________________________________________________________________________ Motivation • Clouds exhibit large geographical, diurnal, seasonal, and interannual variations. • ARM has continuously collected cloud and radiation data for many years at its three primary sites (SGP, NSA, and TWP), which represent a wide range of climatologically important meteorological conditions. • The long-term ARM ground-base measurements are valuable to study statistical characteristics of clouds in different climate regions. Annual Cycle Clouds, Radiation, and LWP Lamont Barrow • Strong seasonal changes in clouds with the maximum cloud amounts seen in Winter and Spring at Lamont, late Summer and early Fall at Barrow, and Southern Hemisphere Summer at Darwin. • Surface albedo has strong seasonal changes at Barrow, associated with changes in snow cover. • Summer maxima in surface downwelling LW are seen at all the three sites. Data Used in the Study The multi-year ARM Climate Modeling Best Estimate (CMBE) cloud and radiation data are used in this study. These data are derived from the ARM Value-Added Products (VAPs): ARSCL, QCRAD, and MWRRET. See the ARM poster by McCoy et al. (2008) for details of the CMBE data. • Cloud fraction from ARSCL • Surface radiative fluxes from QCRAD • Cloud liquid water path from MWRRET Data collected at the ARM SGP Lamont, NSA Barrow, and TWP Darwin sites are analyzed. Darwin Diurnal Cycle • Strong positive correlation between LWP and cloud fraction at Lamont and Darwin while the correlation is weak at Barrow. • Strong negative correlation between LWP and surface downwelling SW at Lamont and Darwin. At Barrow, multiple scattering between the snow covered surface and cloud layers significantly increases SWDN during cold seasons, which leads to a weak correlation between LWP and SWDN. • Strong positive correlation between LWP and surface downwelling LW at Barrow and Darwin while a moderate negative correlation is found at SGP (Why?). Future Work • Characteristics of clouds and radiation at the ARM TWP Manus and Nauru sites will be examined. • Histograms of clouds over the three primary ARM sites will be examined. • Link the observed characteristics of clouds to large-scale conditions. Barrow Lamont Monthly Variation Darwin • Lamont: very strong diurnal variation with late evening maxima in high cloud and noon maxima in low cloud. • Barrow: weak diurnal variation in middle level cloud during Spring, Summer, and Winter seasons. There is little diurnal variability in low cloud. • Darwin: late evening maxima in high cloud and noon maxima in low cloud. Less cloud cover in the Southern Hemisphere Winter. • Cloud fraction and other examined fields show large seasonal variations, but there are no clear year-to-year changes. • Significantly larger low clouds observed over the NSA Barrow site than the SGP Lamont and TWP Darwin sites. Acknowledgments: We thank Eugene Clothiaux, Chuck Long, Dave Turner, Karen Johnson, Michael Jensen, and Yan Shi for their contributions to the CMBE data. This work is supported by the ARM program. ____________________________________________________________________________________________________________________________________________________________________ This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under contract No. DE-AC52-07NA27344. UCRL-Post-401943