Shaocheng Xie, Renata McCoy, and Stephen Klein

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
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Clouds, Radiation, and LWP

• 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
Barrow
Lamont

• 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.
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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