Download Interannual Variations of Arctic Cloud Types:

Interannual Variations of
Arctic Cloud Types:
Relationships with Sea Ice and Surface
Temperature
Ryan Eastman
Stephen Warren
University of Washington
Department of Atmospheric Sciences
Changes in Arctic Temperature
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Rising surface air temperatures since the 1970's
Changes in Arctic Sea Ice
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Declining September sea-ice extent
Clouds & Changes in Arctic Climate
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What is the role of cloud cover in Arctic climate change?
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What is the Cloud Radiative Effect (CRE) in the Arctic?
CRE Defined
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CRE – whether clouds warm or cool the surface
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Two competing effects:
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Longwave (IR) effect
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Shortwave effect
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Surface receives more Infrared Radiation (IR) from a
cloudy sky than from a clear sky – Clouds warm the
surface
Surface receives more sunlight from a clear sky than
from a cloudy sky – Clouds cool the surface
In both cases, low clouds have a greater effect
because they are thicker and composed of water
Effect depends upon season:
CRE in Winter, Longwave Only
Spring/Fall CRE, Shortwave < Longwave
Summer, Shortwave > Longwave
Cloud Detection
Satellite looking down
Surface looking up
Cloud Data

Synoptic surface observations from land (1971-2007)
and ocean (1954-2008)
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Including observations taken from stations drifting on
sea ice
Observations taken daily every three or six hours
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Nighttime observations thrown out if insufficient
moonlight
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Stations specifically chosen to include nighttime obs
Total cloud cover and nine cloud types:
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High cloud (cirriform)
− Middle Clouds: Altocumulus, Altostratus, Nimbostratus
− Low Clouds: Cumulonimbus, Cumulus, Stratus,
Stratocumulus, fog
Arctic Stations
Observations per Year (Hundreds)
From ships and stations
Using These Data...
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Compiled an Arctic cloud climatology for 60° to 90°
North
In this presentation:
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Characterize Arctic cloud cover
Discuss predicted changes in Arctic clouds
Cloud changes at Barrow
Study a sub-dataset over only the Arctic ocean
Cloud trends over the Arctic ocean

Correlations of cloud cover with Arctic sea ice extent and
surface air temperature
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Cloud anomalies in years with high/low ice minima
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Compare with other available Arctic cloud data
Arctic Clouds Through the Year
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From October to April cloudier away from the pole
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From May-September more clouds near the pole
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Because of large presence of low stratiform clouds at
high latitudes during summer
Predicted Arctic Cloud Changes
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By General Circulation Models forced with 2 X CO2
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Cloud cover is predicted to increase
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Low clouds will increase the most
Increase is strongest during the dark season
Precipitation is also predicted to increase
Predicted cloud changes should warm the Arctic
during all seasons but summer
Clouds Changes at Barrow
Clouds Changes at Barrow
Clouds Changes at Barrow
Clouds Changes at Barrow
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Total cloud cover is increasing
Increase is caused mostly by an increase in low
stratiform cloud cover
Seasonal anomalies of total cloud cover are primarily
driven by changes in low stratiform clouds
Any input from residents is appreciated
Trends in Arctic Ocean Cloud Cover

Two regions: Arctic Ocean, and a sub-region called
the 'Beaufort-Laptev' region
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This sub-region is chosen because it is where the seaice edge has been most variable
Study the change in cloud cover in each region based
on linear fits to time series
Summary of Cloud Trends
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Total cloud cover is increasing in all seasons
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Low clouds are most responsible for the trend
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Most significantly in spring and autumn
Stronger increases in Beaufort–Laptev region
Especially low stratiform clouds
Precipitating clouds are decreasing in all seasons
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Surprising, given predicted increases
Not likely due to aerosols, which have decreased
Correlations with Sept. Sea Ice Extent
Correlations with Sept. Sea Ice Extent
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Less
September ice
observed after
cloudy spring
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Cloud
forcing
More autumn
clouds occur
when less ice is
present
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Cloud
response
Correlations with Sept. Sea Ice Extent
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Summer nimbostratus
clouds show a positive
correlation with September
sea ice extent
Correlation with Surface Air Temperature
Correlation Results
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During a year with less ice:
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It is cloudier during spring and autumn
Less precipitating cloud is seen in summer
During a warmer year:
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There is greater cloud cover in winter, spring, and
autumn
Extreme Ice Years
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Low clouds more
prevalent during the
autumn of a low ice
September
Suggests cloud response
to sea-ice retreat
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Less September ice
⇓
More autumn cloud
cover
Arctic Ocean Cloud Study Results
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Cloud changes of recent decades appear to enhance
Arctic Warming
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During winter positive cloud trends may contribute to warm
temperatures
In Summer negative trends in precipitating clouds are
associated with less ice in September
During spring and autumn positive cloud trends are likely
acting to enhance warming and reduce sea ice
Autumn clouds increase after a low-ice September, also
shown by Kay and Gettelman
This work will be available as a paper through the Journal
of Climate
Acknowledgments
Robert Wood, Cecilia Bitz, Mike Wallace, Axel
Schweiger, Xuanji Wang, and Jeff Key for
helpful feedback and discussion

Carole Hahn, Xuanji Wang, Jeff Key, and Axel
Schweiger for making data available
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NSF's Climate Dynamics Program & NOAA's
Climate Change Data and Detection program
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Comparison of Cloud Detection Methods
Satellite Data
Surface Observations
APP-x and Surface
TOVS and Surface
Observations, 60° to 90°N Observations, Ocean Only
Individual Boxes
During DJF
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Interannual variations
in satellite data in all
10° grid boxes are
coherent throughout
the Arctic
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Individual boxes
plotted as gray lines,
Arctic mean is thick
line
Surface observations
do not show this
tendency