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Page 1: Tobias  Bayr and  Dietmar Dommenget

Tobias Bayr and Dietmar Dommenget

The Inhomogeneous Tropospheric Warming as the Driver of Tropical Sea Level Pressure

and Walker Circulation Changes

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Tobias Bayr and Dietmar Dommenget

Tropical Circulation Changes

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Overview

Motivation

Tropical SLP changes

Tropical Circulation changes

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Overview

Motivation

Tropical SLP changes

Tropical Circulation changes

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SLP trend in CMIP3 multi model ensemble (A1B Scenario)

Motivation

Vecchi and Soden (2007)

What drives the Tropical SLP Changes in Global Warming?

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Weakening of the tropical circulations?

Held and Soden (2006), Vecchi and Soden (2007): specific humidity +7 % per K warming [Clausius–Clapeyron]

precipitation increases only by 2 % per K warming

vertical transport -5 % per K warming

weakening of the tropical circulations

Comparable with a widening of a water pipe in a circulation

Motivation

Today Future

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SLP trend in Vecchi and Soden (2007)

What drives the Tropical SLP Changes in Global Warming?

SLP trend in Bayr and Dommenget (2013)

Motivation

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Homogeneous and inhomogeneous surface warming

Total surface warming

Homogeneous warming Inhomogeneous warming

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Overview

Motivation

Tropical SLP changes

Tropical Circulation changes

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Relative Trends of Tropospheric Temperature

Bayr and Dommenget (2013)

surface

1000 – 850 hPa

850 – 500 hPa

500 – 300 hPa

300 – 100 hPa

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Relative warming overOceans Land

Land-Sea Warming Contrast

Inhomogeneous surface warming

Bayr and Dommenget (2013)

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Bayr and Dommenget (2013)

Tropospheric Temperature and SLP Trends

pattern correlation = -0.90

Ttropos relative warming

SLP change

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Mechanism: Bjerknes circulation

Bayr and Dommenget (2013)

T1 = T2

p1 = p2

warming coolingp1 = p2

T1 > T2

p1 < p2

T1 > T2

mass flow

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Tropospheric Temperature and SLP Trends

Bayr and Dommenget (2013)

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Overview

Motivation

Tropical SLP changes

Tropical Circulation Changes

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Zonal Stream function in CMIP5 multi model ensemble

Mean state in 20C

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Zonal Stream function in CMIP5 multi model ensemble

Difference 21C-20C (contours: mean state)

patterncorrelation = -0.48

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Weakening of the zonal circulation cells?

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ECHAM5 AGM Experiments:Homogeneous vs Inhomogeneous warming

Total surface warming

Homogeneous warming Inhomogeneous warming

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InhomogeneousHomogeneous

Diff in Total warming run

Homogenous + Inhomogeneous

ECHAM5 AGM Experiments:Homogeneous vs Inhomogeneous warming

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Conclusions

Tropical SLP change = inhomogeneous Ttropos change (direct Bjerknes Circulation)

Land-Sea Contrast dominates inhomogeneous Ttropos change

Homogeneous and In-homogeneous warming have contrary effects on the Zonal Circulation Cells

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Thank you for your attention!

Bayr and Dommenget:The Tropospheric Land-Sea Warming Contrast as the Driver of Tropical Sea Level Pressure Changes.Journal of Climate, 2013, 26, (4), pp. 1387-1402.