Helmholtz Centre for Ocean Research Kiel, Germany

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Tobias Bayr and Dietmar Dommenget. The Inhomogeneous Tropospheric Warming as the Driver of Tropical Sea Level Pressure and Walker Circulation Changes . Helmholtz Centre for Ocean Research Kiel, Germany. Motivation: What drives the Tropical SLP Changes in Global Warming?. - PowerPoint PPT Presentation

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EGU 2012

Tobias Bayr and Dietmar DommengetThe Inhomogeneous Tropospheric Warming as the Driver of Tropical Sea Level Pressure and Walker Circulation Changes Helmholtz Centre for Ocean Research Kiel, Germany

SLP trend in CMIP3 multi model ensemble (A1B Scenario)Motivation:What drives the Tropical SLP Changesin Global Warming?Vecchi and Soden (2007)22Weakening of the tropical circulationsHeld and Soden (2006), Vecchi and Soden (2007):specific humidity increases 7 % per K warming following the ClausiusClapeyron equation, relative humidity stays constantprecipitation increases only by 2 % per K warming; limiting factor: radiativ coolingvertical transport decreases about roughly 5 % per K warmingweakening of the tropical circulations in global warming w1 > w2Comparable with a widening of a water pipe in a circulation3

SLP trend in Vecchi and Soden (2007)What drives the Tropical SLP Changesin Global Warming?

SLP trend in Bayr and Dommenget (2013)4Homogeneous and inhomogeneous surface warmingTotal surface warmingHomogeneous warmingInhomogeneous warming

5Relative warming overOceans LandLand-Sea Warming Contrast

Inhomogeneous surface warming

Bayr and Dommenget (2013)6

Relative Trends of Tropospheric TemperatureBayr and Dommenget (2013)surface850 500 hPa500 300 hPa300 100 hPa1000 850 hPa7

Bayr and Dommenget (2013)Tropospheric Temperature and SLP Trendspattern correlation = -0.908Mechanism:Bjerknes circulation and HydrostaticBayr and Dommenget (2013) T1 = T2p1 = p2mass flowwarmingcoolinga)b)c)p1 = p2p1 < p2 T1 > T2 T1 > T29In fnf Schritten aufbauen9Tropospheric Temperature and SLP Trends10

Bayr and Dommenget (2013)

Zonal Streamfunction in CMIP5 multi model ensemble11Mean state in 20C11Zonal Streamfunction in CMIP5 multi model ensemble

12Difference 21C-20C (contours: mean state)patterncorrelation = -0.48

13

Weakening of the zonal circulation cells?ECHAM5 AGM Experiments:Homogeneous vs Inhomogeneous warmingTotal surface warmingHomogeneous warmingInhomogeneous warming

14ECHAM5 AGM Experiments:Homogeneous vs Inhomogeneous warmingInhomogeneousHomogeneousDiff in Total warming run

Homogenous + Inhomogeneous

ConclusionThank you for your attention!Reference:Bayr, T., and D. Dommenget (2013), The Tropospheric Land-Sea Warming Contrast as the Driver of Tropical Sea Level Pressure Changes, Journal of Climate, 26, (4), pp. 1387-1402.

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