Point Comparison in the Arctic

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Point Comparison in the Arctic (Barrow - 71.32N,
156.6W ) Part I - Assessing Satellite (and
surface) Capabilities for Determining Cloud
Fraction, Cloud Optical Depth Part II Cloud
effects on Determining Surface TemperaturesTanei
l Uttal, Shelby Frisch, Sunny Sun-Mack, Jeff
Key, Axel SchweigerPatrick Minnis, Xuanji Wang,
Andy Heidinger
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March 2007 March 2009 has been designated The
International Polar Year www.ipy.org The first
IPY was in 1882-1883
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http//www.mnh.si.edu/exhibits/arctic/
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Email Taneil.Uttal_at_noaa.gov to get on the mail
list
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For the Arctic region there is not yet a
consensus about whether or not seasonal cloud
fraction is increasing or decreasing OR if cloud
fraction is a significant measure of cloud
radiative effects OR if clouds are creating a net
warming or a net cooling effect on the Arctic
surface OR the relativeeffect compared to other
Arctic system factors

• Xuanji Wang and Jeffrey R. Key, 2005, Arctic
  Surface, Cloud, and Radiation Properties Based on
  the AVHRR Polar Pathfinder Data Set. Part I
  Spatial and Temporal Characteristics, J. Climate,
  Vol.18, No.14, 2558-2574, 2005.
• Xuanji Wang and Jeffrey R. Key, 2004, Arctic
  Surface, Cloud, and Radiation Properties Based on
  the AVHRR Polar Pathfinder Data Set. Part II
  Recent Trends, J. Climate, Vol.18, No.14,
  2575-2593, 2005.
• Jennifer A. Francis, Elias Hunter, Jeffrey R.
  Key, and Xuanji Wang, 2005, Clues to Variability
  in Arctic Minimum Sea Ice Extent, Geophys. Res.
  Lett., Vol.32, L21501, doi10.1029/2005GL024376,
  2005.
• Schweiger, Axel. J. Changes in seasonal cloud
  cover over the Arctic seas from satellite and
  surface observations, Geophysical Research
  Letters, Vol 31, L12207, doi10.1029/2004GL020067,
  2004.
• Intrieri, J.M., C.W. Fairall, M.D. Shupe, P.O.G.
  Persson, E.L. Andreas, P. Guest, and R.M. Moritz,
  2002 An annual cycle of Arctic surface cloud
  forcing at SHEBA. J. Geophys. Res., 107(C10),
  doi10.1029/2000JC000439
• Zuidema, P., B. Baker, Y. Han, J. Intrieri, J.
  Key, P. Lawson, S. Matrosov, M. Shupe, R. Stone,
  and T. Uttal, 2005 An Arctic sprintime
  mixed-phase cloudy boundary layer observed during
  SHEBA. J. Atmos. Sci., 62, 160-176.
• Shupe, M.D., and J.M. Intrieri, 2004 Cloud
  radiative forcing of the Arctic surface The
  influence of cloud properties, surface albedo,
  and solar zenith angle. J. Climate, 17, 616-628

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8 years of data from the North Slope of Alaska
DOE/ARM site
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New radar-lidar-radiometer facility in Eureka,
Canada since Aug 2005
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Ground-based Radar
CLDSAT
Eureka 80N 86W July 3 2006
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APPROACH Focus cloud fraction and cloud
optical depth studies on Barrow where there are
independent surface-based measurements (will add
Eureka, Canada as a second comparison site)
Compare monthly averages without regard to the
different temporal and spatial sampling
issuesAssume the satellite and surface data
sets are now long enough to produce meaningful
statistical comparisons of annual and interannual
variability
Part I Assessing Satellite Capabilities for
Determining Cloud Fraction, Cloud Optical Depth
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Radar Data Disclaimer
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Monthly Average Cloud Fraction( indicate months
will less than 15 days of radar data)
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Monthly Averages of Annual Cycle of Cloud Fraction
Note APPX data calculated from 1998-2000 CERES
TEAM data calculated from 2000-2003 Radar data
calculated from 1998-2004 TOVS data calculated
from 1997-2006 PATMOSX data calculated from 1998
to 2004
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Many satellite to surface comparisons have
focused on cloud fraction. In the Arctic, cloud
optical depth appears to be a much more important
parameter in defining the radiative impact of
clouds on the surface(Also noted by Dr.
Hayasaka)
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Zuidema et al.2005
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Figure from Shupe, 2004 using data over the
Arctic Ocean (SHEBA)
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Monthly Averages of Cloud Optical Depth(
indicate months will less than 15 days radar of
data)
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Monthly Averages of Annual Cycle of Cloud Optical
Depth
Note APPX data calculated from 1998-2000 CERES
TEAM data calculated from 2000-2003 Radar data
calculated from 1998-2004
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Part II Assessing Satellite Capabilities for
Determining Surface Temperature

• APPROACH
• Focus surface temperature comparisons on weather
  station sites that are or will be the location of
  future Atmospheric observatories
• Examine monthly averages of surface temperature
  partitioned by cloud fraction
• Dont assume that the surface temperature
  measurements at the surface are correct

Surface Meteorological Data Disclaimer
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Monthly means of surface temperature (in-situ
daily mean) APPX surface temperature (0400 and
1400 LST average) for 1982-2000
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Solid Line Surface Grey Line APPX Dashed
Line Corrected APPX
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• Preliminary Conclusions and Work in Progress
• Monthly mean values of cloud fraction are in good
  agreement between the AVHRR (APPX), TOVS (Polar
  Pathfinder), MODIS (CERES-TEAM), and surface
  measurements. WE CAN TRUST OUR SEASONAL CYCLE
  MEASUREMENTS OF CLOUD FRACTION IN THE ARCTIC
• Monthly mean values of cloud optical depth is
  more problematic. The AVHRR (APPX) appears to
  have problems with detecting annual trends in
  optical depth. The MODIS (CERES-TEAM) does
  better with annual trends but the summer values
  of optical depth in summer time are considerably
  lower than the retrievals from the surface.
  IMPROVED RETRIEVAL OF OPTICAL DEPTH SHOULD BE A
  PRIORITY
• Data from Barrow, SHEBA and Eureka show
  significant supercooled liquid water in Arctic
  clouds in all seasons DONT ASSUME ARCTIC CLOUDS
  ARE ALL ICE

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The surface data has calibration errors,
operational problems, data gaps, and more DONT
ASSUME THE SURFACE DATA IS TRUTH The APPX
surface temperature measurements appear to have
biases compared to the surface that change as a
function of cloud fraction, season, and location.
In general APPX surface temperatures are too
cold in the summer and too warm in the winter.
NEED TO INVESTIGATE SEASONAL AND REGIONAL
CORRECTIONS SINCE THE ARCTIC IS SO CLOUDY AND WE
NEED THE SATELLITES FOR SURFACE
TEMPERATURE Preliminary results indicate that
the Arctic has important sub-regions, with
significant differences in cloud properties. OVER
AVERAGING OF CLOUD CLIMATOLOGIES MAY BE
PARTICULARLY PROBLEMATIC FOR THE ARCTIC FORGET
THE LATITUDINAL AVERAGING