Summit Talk

8/3/2019 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

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