Post on 22-Feb-2016
description
Tobias Bayr and Dietmar Dommenget
The Inhomogeneous Tropospheric Warming as the Driver of Tropical Sea Level Pressure
and Walker Circulation Changes
Tobias Bayr and Dietmar Dommenget
Tropical Circulation Changes
Overview
Motivation
Tropical SLP changes
Tropical Circulation changes
Overview
Motivation
Tropical SLP changes
Tropical Circulation changes
SLP trend in CMIP3 multi model ensemble (A1B Scenario)
Motivation
Vecchi and Soden (2007)
What drives the Tropical SLP Changes in Global Warming?
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
SLP trend in Vecchi and Soden (2007)
What drives the Tropical SLP Changes in Global Warming?
SLP trend in Bayr and Dommenget (2013)
Motivation
Homogeneous and inhomogeneous surface warming
Total surface warming
Homogeneous warming Inhomogeneous warming
Overview
Motivation
Tropical SLP changes
Tropical Circulation changes
Relative Trends of Tropospheric Temperature
Bayr and Dommenget (2013)
surface
1000 – 850 hPa
850 – 500 hPa
500 – 300 hPa
300 – 100 hPa
Relative warming overOceans Land
Land-Sea Warming Contrast
Inhomogeneous surface warming
Bayr and Dommenget (2013)
Bayr and Dommenget (2013)
Tropospheric Temperature and SLP Trends
pattern correlation = -0.90
Ttropos relative warming
SLP change
Mechanism: Bjerknes circulation
Bayr and Dommenget (2013)
T1 = T2
p1 = p2
warming coolingp1 = p2
T1 > T2
p1 < p2
T1 > T2
mass flow
Tropospheric Temperature and SLP Trends
Bayr and Dommenget (2013)
Overview
Motivation
Tropical SLP changes
Tropical Circulation Changes
Zonal Stream function in CMIP5 multi model ensemble
Mean state in 20C
Zonal Stream function in CMIP5 multi model ensemble
Difference 21C-20C (contours: mean state)
patterncorrelation = -0.48
Weakening of the zonal circulation cells?
ECHAM5 AGM Experiments:Homogeneous vs Inhomogeneous warming
Total surface warming
Homogeneous warming Inhomogeneous warming
InhomogeneousHomogeneous
Diff in Total warming run
Homogenous + Inhomogeneous
ECHAM5 AGM Experiments:Homogeneous vs Inhomogeneous warming
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
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.