1. Causes of Reduced North Atlantic Storm Activity in A Global Climate Model Simulation of the Last Glacial Maximum Aaron Donohoe, David Battisti, Camille Li University of Washington Department of Atmospheric Sciences

2. Last Glacial Maximum (LGM) run in CCSM3 Otto-Bliesner et al. (2006) 21ka Insolation Greenhouse Gas Concentration from ice core measurements Land Ice Topography and coastlines corresponding to a 120 meters sea level depression from ICE-5G reconstruction (Peltier 2004)

3. Mean State (DJF) Atlantic Jet

4. Eady Growth Rate Per Day Contours = 250 hPa Zonal Wind. LGM MODERN

5. Eddy Activity Vertically Averaged DJF eddy Variances Contours = 250 hPa Zonal Wind (m/s)

6. Linear Stability Of Jet Hypothesis: Strong LGM Barotropic Shear Stabilizes the Jet to Baroclinic growth This idea is tested with a 2-layer, QG, linear Model Conclusion: The jet structure stabilizes the LGM as compared to the Modern jet relative to the Eady Growth rate BUT the LGM is still more linearly unstable to Baroclinic eddies MODERN LGM

7. Feature Tracking Z 300 hPa Use the feature tracking algorithm of Hodges on 2-10 day band pass filtered 300 hPa geopotential height 25 years of data give in each run allow us to compute instantaneous central magnitude and tendency

8. Feature Tracking By Zonal Location

9. Atlantic Domain Ensemble Feature Statistics SEED MAGNITUDE

10. Conclusions Storm activity is reduced in the LGM simulation despite enhanced baroclinicity relative to the modern day The narrowness of the LGM jet can not explain the reduced storm activity Reduced seeding (magnitude and number) seems to explain the decreased LGM storm activity despite more efficient baroclinic growth

11. The Eddy Kinetic Energy Budget

12. Eddy Kinetic Energy Budget Energy Conversion Eddy Kinetic Energy Reservoir Changes in Barotropic Decay between modern and LGM work in the wrong sense to explain reduced LGM storm activity Changes in Baroclinic conversion are indicative of differences in eddy kinetic energy reservoir