Arctic clouds, circulation, and sea ice during 2007 and beyond
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Transcript of Arctic clouds, circulation, and sea ice during 2007 and beyond
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Arctic clouds, circulation, and sea ice during 2007 and beyond
Jennifer Kay1,2, Andrew Gettelman1,
Kevin Reader1, and Tristan L’Ecuyer2
1National Center for Atmospheric Research (NCAR)1Colorado State University (CSU)
MODIS Image from March 10, 2008 (sea ice maximum extent)
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MODIS Image from March 26, 2008
1. Lessons and questions from 20072. Data assimilation project (CAM-DART)3. Early observations for 2008
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“A perfect storm” for ice loss in 2007
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Cloud and radiative flux differences(2007-2006)
Radiative fluxes from 2B-FLXHR produced by Tristan L’Ecuyer (CSU).
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Were the 2007 clouds really anomalous?
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In a warmer world with thinner ice, natural summertime circulation and cloud variability is an increasingly
important control on sea ice extent.
Kay, L’Ecuyer, Gettelman, Stephens, and O’Dell(Geophysical Research Letters, 2008)
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For clouds, timing is key.
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Atmospheric forcing on sea ice loss
Barrow, Alaska (ARM) July
avg 2007
September
avg 2007
Total Cloud Cover 0.72 0.60 0.90 0.84
Downwelling Surface LW (Wm-2 ) 302 305 300 300
Downwelling Surface SW (Wm-2 ) 209 238 53 53
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Many remaining questions
1) thermodynamic vs. dynamic loss processes2) cloud-ice-circulation feedbacks3) year-to-year variability vs. long-term ice thinning4) models: reliability?, what can they teach us?5) tipping point? 2008?
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MODIS Image from April 13, 2008
1. Lessons and questions from 20072. Data assimilation project (CAM-DART)3. Early observations for 2008
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Why DART?DART = Data Assimilation Research Testbed
Fig. 1 from Rodwell and Palmer (2007)
Science Questions- Do climate models capture observed changes in the atmospheric forcing on sea ice loss? - How does the Arctic ocean surface affect the Arctic atmosphere?
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CAM-DART vs. NCEP
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DART-CAM Assimilations
Name Surface boundary condition
July06obs observed (Hurrell et al., 2008)
July07obs observed (Hurrell et al., 2008)
July07clim climatological SST and sea ice
Science Questions For Today- How well do CAM/DART reanalyses capture observed changes? (July06 vs. July07)- Does the surface affect the best guess of the atmospheric state? (July07sst vs. July07clim)
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CAM-DART July06 vs. July07
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July07 CAM-DART obs vs. climo
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July07 vs. Sept07 sea ice extent
Source: NSIDC
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MODIS Image from May 19, 2008
1. Lessons and questions from 20072. Data assimilation project (CAM-DART)3. Early observations for 2008
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NCEP During 08 Ice Melt
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Clouds During 08 Ice Melt
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Summary
- In a warmer world with thinner ice, the minimum sea ice extent is increasingly sensitive to year-to-year variability in weather and cloud patterns.- The timing of ice loss matters.- CAM-DART can qualitatively reproduce observed changes in the atmospheric forcing on sea ice.- 2008 atmospheric circulation and cloud anomalies are small. But… If the current anti-cyclonic pattern persists/strengthens, there will be significant sea ice loss in 2008.
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EXTRA SLIDES
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NCEP During 08 Ice Growth
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Clouds During 08 Ice Growth
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Early Fall Cloud Increases (‘07-’06) Near The Dateline
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2007 Arctic sea ice extent
The sea ice extent at the 2007 minimum was 4.13 million km2
down 43% from 1979 and down 26% from the last record minimum in 2005.
Credit: NSIDC
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Sea Ice Extent: July vs. Sept, 06 vs. 07
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DART-CAM noise slide
PSL map fc_time=0,3,6 hours
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Fall/Winter Clouds/LW
Rad at ARM Barrow
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Western Pacific Arctic
Variable 2007-2006 JulyCERES FlashFlux, Barrow
2007-2006 JJACloudSat/CALIOP, Barrow
Total Cloud Cover n/a, -0.13 -0.16, -0.15
TOA Albedo - 0.07, n/a n/a, n/a
FSDS (Wm-2 ) + 26, + 28 + 32, + 25
FSNS (Wm-2 ) + 19, n/a n/a, n/a
FLDS (Wm-2 ) + 8, + 2 -4, -1
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Western Pacific Arctic Data2007-2006
CERES FlashFlux
2007-2006Barrow, AK
July Sept July Sept
Total Cloud Cover - - -0.13 -0.06
TOA Albedo - 0.07 - 0.07 - -
TOA Albedo (clear) - 0.11 - 0.15 - -
FSDS (Wm-2 ) + 26 + 4 + 28 + 3
FSNS (Wm-2 ) + 19 + 9 - -
FLDS (Wm-2 ) + 8 + 20? + 2 - 5?
Variable 2007-2006 JJA in WPACloudSat/CALIOP, ARM Barrow
Total Cloud Cover -0.16, -0.15
FSDS (Wm-2 ) + 32, +25
FLDS (Wm-2 ) -4, -1
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2007 Western Arctic cloud reductions
CloudSat/CALIOP data revealed reduced cloudiness and enhanced downwelling shortwave radiation (+32 Wm-2).