Transcript EGU 2012 - Helmholtz-Zentrum fu\u0308r Ozeanforschung Kiel

The Inhomogeneous Tropospheric Warming
as the Driver of Tropical Sea Level Pressure
and Walker Circulation Changes
Tobias Bayr and Dietmar Dommenget
Tropical Circulation Changes
Tobias Bayr and Dietmar Dommenget
Overview
Motivation
Tropical SLP changes
Tropical Circulation changes
Overview
Motivation
Tropical SLP changes
Tropical Circulation changes
Motivation
What drives the Tropical SLP Changes in Global Warming?
SLP trend in CMIP3 multi model ensemble (A1B Scenario)
Vecchi and Soden (2007)
Motivation
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


Þ vertical transport -5 % per K warming
Þ weakening of the tropical circulations
Today
Future
Comparable with a widening of a water pipe in a circulation
Motivation
What drives the Tropical SLP Changes in Global Warming?
SLP trend in Vecchi and Soden (2007)
SLP trend in Bayr and Dommenget (2013)
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
300 – 100 hPa
500 – 300 hPa
850 – 500 hPa
1000 – 850 hPa
surface
Bayr and Dommenget (2013)
Land-Sea Warming Contrast
Relative warming over
Oceans
Land
Inhomogeneous surface warming
Bayr and Dommenget (2013)
Tropospheric Temperature and
SLP Trends
Ttropos relative warming
SLP change
pattern correlation = -0.90
Bayr and Dommenget (2013)
Mechanism: Bjerknes circulation
mass flow
T1
=
T2
p1 = p2
warming
cooling
T1
p1
>
=
T2
p2
T1
p1
>
<
T2
p2
Bayr and Dommenget (2013)
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
ECHAM5 AGM Experiments:
Homogeneous vs Inhomogeneous warming
Diff in Total warming run
Homogeneous
Inhomogeneous
Homogenous + Inhomogeneous
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.