1. Can Arctic Sea Ice Summer Melt be Accelerated by Changes in Spring Cloud Properties? I. Gorodetskaya 1, B. Tremblay 1,2, B. Liepert 1, M. Cane 1 1 Lamont-Doherty Earth Observatory, New York 2 McGill University, Montreal

2. yes

3. surface radiative fluxes Data: SHEBA Atmospheric Surface Fluxes Group atmosphere

4. Cloud phase and long-wave: FebruaryMarchApril WINTER->SPRING

5. Cloud phase and long-wave: SPRING->SUMMER MayJune July

6. Cloud LW forcing (CFL) as a function of cloud properties Chen, Aires, Francis, Miller, J Climate 2006

7. Liquid water path: data and models Gorodetskaya et al, accepted to J Climate

8. Total variance in the perennial ice edge attributable to anomalies in forcing parameters, 1980-2004 also see: Francis, Hunter, Key, Wang, JRL 2005 J. A. Francis and E Hunter

9. - Spring: large positive trend Schweiger, GRL 2004 - Summer: no trend … Cloud cover over the Arctic Ocean:

10. April and May have the largest trends in both Cloud % and LW flux R(LW,CLT)=0.6 TOVS

11. Changes in Arctic (white bars) annual mean sea ice extent at the end of the 21st century Arzel, Fichefet, Goosse, Ocean Modelling 2006

12. CCSM3: predicts a large increase in the Arctic annual mean downwelling LW flux in the 21 st century

14. Winter&SPRING! increase in cloud liquid water path: increase in LW flux down:

15. Total downwelling flux difference between the last and first decades of 21 st century

16. 0-layer thermodynamics model: sea ice thickness and concentration evolution Ta - from NP drifting stations (Lindsay, J Climate 1998) LW, SW ice: A,h Fc Ti Tb=-1.8 LW, SW, Fsens, Flat Fsens(Ta-Ti), Flat

17. Scale the forcing with the CCSM-predicted changes in downwelling LW and SW fluxes

18. Sea ice thickness change:

19. conclusions and outlook Clouds increase: Apr 21%, May 12% (1980-2004) => Arctic Ocean gains ~15 W/m 2 more LW radiation (TOVS data) NCAR CCSM3: -Arctic - more liquid clouds in 2xCO 2 world -spring cloud LW warming overwhelms SW cooling with the above cloud response alone (LW forcing strongest in winter and spring), a 1D ice model reduces an equilibrium sea ice thickness from 4.5 to 2.5 m positive feedbacks not included! e.g., snow(T) -> surface albedo

20. Arctic Sea Ice Summer Melt can be accelerated by an increase in Spring cloud liquid water path... Big Thanks: Yonghua Chen, Jennifer Francis, Kirstie Stramler, Martin Vancoppenolle, Richard Cullather Photo from Peter Minnett