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A consistent poleward shift of storm tracks? Yin 2005 • Storm track (SD of daily MSLP): A1B-20C (DJF) • Response is if anything a southward shift in the North Atlantic. • Spread > mean in NH. Zonal mean temperature changes Stratosphere cools, Tropopause lifts Increased Teq - Tpole Decreased Teq - Tpole SRESA1B IPCC AR4 Regional forcing Sea-ice retreat MOC weakening Land-sea contrast Tropical SSTs -> stationary waves Zonally symmetric sensitivity experiments have been done before. In WP2 we will use HadGAM1 with full orography. WP2.1 Global forcing: • Globally uniform SST rise • Increase CO2 only • Both WP2.2 Regional forcing: • North Atlantic SST • Decreased sea-ice • Land-sea temperature contrast Some runs to test linearity Lorenz and DeWeaver 2007 What effect will increased moisture have? More latent heating => stronger storm growth => more intense storm track OR More latent heating => more efficient heat transport => weaker storm track Other things to think about: • Hard to separate moisture increase and upper level temperature gradient • Test sensitivity to basic state – eg using model and observed background SSTs NAM The climate change signal is baroclinic, so the choice of level matters. May apply to storms as well – eg HernandezDeckers…? Climate change How do we include things like this? Selten et al (2004) Hypothesis: MOC weakening is very important IPCC AR4 EOF1 of temperature response across models explains ~1/2 of the spread in wind response over Europe. Regression on the MOC response in the models gives very similar patterns. Linear regression suggests that the weakening of the MOC is the dominant contributor to the ensembel mean storm track response.