Download Interannual Variations of Arctic Cloud Types:

Interannual Variations of
Arctic Cloud Types:
Relationships with Sea Ice and Comparisons
with Satellite Observations
Ryan Eastman
Stephen Warren
University of Washington
Department of Atmospheric Sciences
Changes in Arctic Climate

What is the role of cloud cover in Arctic climate change?

What is the Cloud Radiative Effect (CRE) in the Arctic?
CRE depends on season, cloud type


CRE – whether clouds warm or cool the surface
Longwave (IR) effect dominates during autumn, winter
and spring
−

Shortwave effect dominates during summer
−

Due to a higher sun and no snow on top of sea ice
Shupe & Intrieri (2003), using SHEBA data, conclude
that phase, temperature, and height all have a strong
impact on CRE
−

Due to low sun angles and a high surface albedo
Water clouds are warmer, usually thicker, and stronger
emitters
Effects of cloud changes depend on the type of cloud
and the season of the change
Cloud Detection
Satellite looking down
Surface looking up
Cloud Data

Synoptic surface observations from land (1971-2007)
and ocean (1954-2008)
−


Including observations taken from stations drifting on
sea ice
Observations taken daily every three or six hours
−
Nighttime observations thrown out if insufficient
moonlight
−
Stations specifically chosen to include nighttime obs
Total cloud cover and nine cloud types:
−
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...


Compiled an Arctic cloud climatology for 60° to 90°
North
For this presentation:
−
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

Cloud anomalies in years with high/low ice minima

−
Compare with other available Arctic cloud data
Correlations with Sept. Sea Ice Extent
Correlations with Sept. Sea Ice Extent

Less
September ice
observed after
cloudy spring
−

Cloud
forcing
More autumn
clouds occur
when less ice is
present
−
Cloud
response
Correlations with Sept. Sea Ice Extent

Summer nimbostratus
clouds show a positive
correlation with September
sea ice extent
Correlation with Surface Air Temperature
Superposed Epochs


Determine the years with greatest and least
September sea ice extent for the period 1979 to 2007
Calculate the average percent cloud cover for each
cloud type for the 5 highest and 5 lowest ice years
Superposed Epochs
Results


Low clouds more
prevalent during the
autumn of a low ice
September
Suggests cloud response
to sea-ice retreat
−
Less September ice
⇓
More autumn cloud
cover
Arctic Ocean Cloud Study Results

Cloud changes of recent decades appear to enhance
Arctic Warming
−
−
−


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, as
also shown by Kay and Gettelman
This work has been submitted to Journal of Climate
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

Interannual variations
in satellite data in all
10° grid boxes are
coherent throughout
the Arctic
−

Individual boxes
plotted as gray lines,
Arctic mean is thick
line
Surface observations
do not show this
tendency
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
NSF's Climate Dynamics Program & NOAA's
Climate Change Data and Detection program