The contribution of cloud and radiation anomalies to the 2007 Arctic sea ice minimum
Jennifer E. Kay (jenkay@ucar.edu)1,2, Tristan L’Ecuyer2, Andrew Gettelman1, Graeme Stephens2, and Chris O’Dell2 1 National Center for Atmospheric Research, Climate and Global Dynamics 2 Atmospheric Sciences, Colorado State University
Quick Summary
Cloud decreases and downwelling shortwave radiation increases associated with an anticyclonic atmospheric circulation pattern contributed to the dramatic summer 2007 Arctic sea ice loss (F1).
1. Dramatic Sea Ice Loss in 2007
Although sea ice extent has been declining, the extent loss during summer 2007 was surprisingly large (F2, Stroeve et al., (2008)).
8 September Ice Extent (million km2) 7 6 5 4 1979 The 2007 minimum ice extent was 22% down from the last record minimum in 2005!
4. Historical Context for 2007 Loss
The 2007 clouds, radiative fluxes, and circulation patterns are anomalous in the recent past, but are not unprecedented (e.g., F5).
Average JJA Downwelling LW Irradiance (Wm-2) Average JJA Downwelling SW Irradiance (Wm-2)
235 225 215 205 195 185 175 0.95 0.90 0.85 0.80 0.75 0.70 1946 1956 1966 1976 1986 1996 2006 1999 2001 2003 2005 2007 335 325 315 305 295 285 275
1986
1993
2000
2007
2. 2007-2006 Clouds and Radiative Fluxes
Mean Sea Level Pressure (mb) 1008 1014 1022
September 16, 2007 sea ice extent
Cloudiness decreased by 16%, downwelling shortwave (longwave) radiation increased by 32 Wm-2 (-4 Wm-2) in the Western Arctic (F1, F3). These radiation differences alone could lead to 0.3 m of surface melt OR warm the surface ocean by 2.4 K.
13.9 11.5 8.6 5.8 2.9 0.0 13.9 11.5 8.6 5.8 2.9 0.0 50 Height asl (km) Height asl (km)
Summertime Cloud Fraction
2006
0.60 0.45 0.30 0.15 0.00 From 2006 to 2007, cloud reductions occurred at heights poleward of 70 N!
F5. Surface observations from Barrow, AK: ARM NSA downwelling fluxes (top), ISH cloud observations (bottom)
5. Implications and Future Work
In a warmer world with thinner ice, natural cloud and circulation variability will play an increasingly important role in controlling sea ice extent (Kay et al., GRL).
2007
Downwelling SW Radiation (W m-2)
60 70 80 Latitude (deg N)
90
-120
0
120
F3. Summertime Western Arctic cloudiness estimated from CloudSat and CALIOP
3. 2007 Arctic Atmospheric Circulation
Cloud decreases resulted from a persistent anti-cyclonic circulation pattern (F4). In addition to reducing cloud cover, this pattern resulted in strong southerly winds that pushed ice into the Central Arctic and enhanced poleward atmospheric heat advection.
10 8 6 4 2 0 -2 -4 -6 -8 -10 Sea Level Pressure (mb) 850 mb Temperature (deg C) 5 4 3 2 1 0 -1 -2 -3 -4 -5 Surface Wind (m/s) 5 4 3 2 1 0 -1 -2 -3 -4 -5
Downwelling LW Radiation (W m-2)
-40
0
40
References/Acknowledgements
Kalnay, E. et al. (1996), The NCEP/NCAR Reanalysis 40-year Project, BAMS, 77, 437-471. Kay, J. E. et al., (in review), The contribution of cloud and radiation anomalies to the 2007 Arctic sea ice minimum, GRL. Stroeve, J. et al. (2008), Arctic sea ice plummets in 2007, EOS Transactions, 89, 13. JEK is funded by the NASA CloudSat project with additional support from NCAR (NSF). We thank Marika Holland and Clara Deser for helpful conversations.
F1. Summer 2007 circulation and minimum ice extent (top), 20072006 summertime flux differences estimated from CloudSat and CALIOP (middle, bottom)
F4. Summer 2007 NCEP anomaly maps (Kalnay et al., 1996)
JJA Cloud Fraction
F2. September Arctic sea ice extent (credit: NSIDC)
We are currently examining the potential for cloud-circulation-ice feedbacks during the 2007 sea ice loss, monitoring current Arctic ice, cloud, and circulation patterns, and evaluating the representation of atmospheric forcing on sea ice in NCAR’s climate model.