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)

MODIS Image from March 26, 2008

1. Lessons and questions from 20072. Data assimilation project (CAM-DART)3. Early observations for 2008

“A perfect storm” for ice loss in 2007

Cloud and radiative flux differences(2007-2006)

Radiative fluxes from 2B-FLXHR produced by Tristan L’Ecuyer (CSU).

Were the 2007 clouds really anomalous?

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)

For clouds, timing is key.

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

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?

MODIS Image from April 13, 2008

1. Lessons and questions from 20072. Data assimilation project (CAM-DART)3. Early observations for 2008

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?

CAM-DART vs. NCEP

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)

CAM-DART July06 vs. July07

July07 CAM-DART obs vs. climo

July07 vs. Sept07 sea ice extent

Source: NSIDC

MODIS Image from May 19, 2008

1. Lessons and questions from 20072. Data assimilation project (CAM-DART)3. Early observations for 2008

NCEP During 08 Ice Melt

Clouds During 08 Ice Melt

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.

EXTRA SLIDES

NCEP During 08 Ice Growth

Clouds During 08 Ice Growth

Early Fall Cloud Increases (‘07-’06) Near The Dateline

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

Sea Ice Extent: July vs. Sept, 06 vs. 07

DART-CAM noise slide

PSL map fc_time=0,3,6 hours

Fall/Winter Clouds/LW

Rad at ARM Barrow

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

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

2007 Western Arctic cloud reductions

CloudSat/CALIOP data revealed reduced cloudiness and enhanced downwelling shortwave radiation (+32 Wm-2).