Summit Talk
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Transcript of Summit Talk
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NOAAs contribution
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M. Shupe
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Microwave Radiometers:
PWV, LWP, T
Spectral Infrared Interferometer:Cloud phase, microphysics, LW radiation, trace gases
Cloud Radar: Cloud macrophysics,phase, microphysics, dynamics
Ceilometer:
Cloud base
Depolarization Lidars:
Cloud base, phase,
microphysics, orientation
Sodar:
Boundary layer depth
Radiosonde:
T, RH, Winds
Precip Sensor:
Rate, PSD?
M. Shupe
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Ceilometer shows
cloud base
Small depol ratio = liquid
Generally, higher reflectivity
values indicate ice clouds or
precip
Larger spectral
widths indicate
turbulence (to first
order)
Large backscatter
indicates liquid
layers
Large depol ratio = ice
High LWP shows
lots of liquid in
column
M. Shupe
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Ice is less opaque in the
IR so the atmospheric
window opens when
liquid layer gone
Brightness Temp (K)
M. Shupe
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12 Z Sounding 24 Z Sounding
10 15 20 24
Time (UTC)M. Shupe
M. Shupe
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Monthly cloud fractions are important for:
- Determining the energy budget In the Arctic, clouds warm the surface
- Validating climate model cloud parametizations
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Comparing Summit tothe Rest of the Arctic
Shupe et al. (20??)
Minimums in January, February, March, or April
August and September maximums
Same basic pattern but varies slightly from location to location
Depends on synoptic features, geography, etc..
OVERALL, THE ARCTIC IS A VERY CLOUDY PLACE!
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Satellite-Based ObservationsUsing CloudSat
CloudSat has complete
spatial coverage (save northof 83o) and frequent
overpasses of high latitudes
Cloud occurrence fractions
were determined for all of
Greenland using CloudSat
and CalipsoONE WEEK OF OVERPASSES
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CloudSAT June 2010 April 2011
Comparison toOther Satellite-
Derived AnnualCloud Fractions
AVHRR
1982-2004
MODIS
2000-2005
ATSR-2
1997
Griggs & Bamber (2007) Good agreement!
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CloudSAT June 2010 April 2011
Comparison toReanalysis Annual
Cloud FractionsERA-40
1982-2001
NCEP-DOE
1982-2004
NCEP-NCAR
1982-2004
Griggs & Bamber (2007)
ISCCP
1983-1999
Reanalysis datasetsare poor over the
Greenland Ice Sheet!
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June 2010 April 2011
M. Shupe
M. Shupe
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Comparing the Cloud Radarat Summit to CloudSat
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MMCR averaged over 1 minute
centered on overpass time
CloudSat averaged over 15 data
points centered on the closest data
point to Summit
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* Reflectivity values and
cloud boundaries agree well
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Distant Overpass, Good Agreement
Close Overpass, Good Agreement
Distant Overpass, Poor Agreement
Close Overpass, Poor Agreement
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Exploring the Averaging Timesfor the Comparison
X
Is X really the best
point? Or is it just a
coincidence of the
data averaging?
20 kmph
50 kmph35 kmph
Possible explanation:
The winds at cloud
height may beaveraging 35 km/h,
But this assumes
overpasses are
parallel to wind
vectors
D O Di M
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Does Overpass Distance Matter?
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Difference (Not Absolute) vs. Altitude
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Difference vs. HAGL
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Directly Comparing IndividualMeasurements
A direct comparison of CloudSat measured
reflectivity to the corresponding MMCR
measured reflectivity. There is a general
agreement below -15 dBZ, but for larger
reflectivities, CloudSat measures lower values
(i.e. slope greater than 1)
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Summit v s. Barrow, AK
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Physical Explanation of Slope
CloudSat MMCR The different scattering regimes
for given particle sizes and
radiation wavelengths is shown.
The wavelengths for Cloudsat
and the MMCR are shown in red
and blue, respectively. Notice
that Cloudsat enters the Mie
regime at smaller particle sizes
than does the MMCR
Mostly cloud particles
Mostly precipitation
Petty (2006)
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Limitations of the Comparison
COMPARISON:Percent of time a cloud was
detected
TAKE-AWAYS:
Fairly good agreement
from 1 to 6 km
CloudSat does not see
the thinner high (> 6km)
clouds
CloudSat cannot see the
low, stratiform clouds
which are the most
abundant clouds in the
Arctic (< 1km)
Barrow Cloud Occurrence vs. HAGL
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Thank You
KANGERLUSSUAQ,
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KANGERLUSSUAQ,
GREENLAND
Some photos courtesy of Eric Parker and Nate Miller
OVER THE ICE SHEET
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OVER THE ICE SHEET
SUMMIT
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SUMMIT,
GREENLAND