CH2018: Multi-member ensemble simulations to explore decadal variability

Stefan Broennimann1,2, Marco Rohrer1,2, Christoph C. Raible2,3

1 Institute of Geography, University of Bern, Switzerland2 Oeschger Centre for Climate Change Research, University of Bern, Switzerland3 Climate and Environmental Physics, Physics Institute, University of Bern, Switzerland

Overview

• Available Simulations

• Drought years during 1945 -1952

• Decadal variability of European heatwaves

• Decadal changes of atmospheric blocking

• Adds2

SimulationsModel:• ECHAM5.4

• Resolution: T63/L31 up to 10hPa

3

SimulationsModel:• ECHAM5.4

• Resolution: T63/L31 up to 10hPa

Forcing: • SST reconstruction (Mann et al. 2008)

• Solar irradiance (Lean 2000)

• Volcanic eruptions (Crowley et al. 2008)

• GHG (as used in Yoshimori et al. 2010)

• Land use (Pongratz et al. 2008), bug!!!

• Aerosols (Koch et al. 1999) before 1850 constant

4

SimulationsModel:• ECHAM5.4

• Resolution: T63/L31 up to 10hPa

Forcing: • SST reconstruction (Mann et al. 2008)

• Solar irradiance (Lean 2000)

• Volcanic eruptions (Crowley et al. 2008)

• GHG (as used in Yoshimori et al. 2010)

• Land use (Pongratz et al. 2008), bug!!!

• Aerosols (Koch et al. 1999) before 1850 constant

Ensemble approach• Different initial conditions obtained from a 1600 AD control simulation

• 30 ensemble members, 28 normally used

5

Evaluation

6

Known shortcomings:

• Land surface: only 9 from 14 types are implemented

• SST variability too low due to reconstruction method

• Sea ice constant before 1870

Evaluation

7

Drought years during 1945 -1952

8Broennimann (2015, in press)

1952

1950

1949

1947

1945

Observation Esemble meanObservation Esemble mean

Decadal variability of European heatwaves

9Broennimann (2015, in press)

Reconstructed AMO and simulated area fraction for US and Europe when max. temperature excceeds the 90th percentile (1901-2000)

Ensemble mean Ensemble ranges «best» member

-0.1

-0.2

0.0

0.1

AM

O (

C)

Decadal changes of atmospheric blocking

10

Winter Blocking Frequency in North Atlantic/Europe (-70 to10E, 40 to 80N; Member 025)

Rohrer et al. (xxx)

Decadal changes of atmospheric blocking

11

Winter Blocking Frequency: Ensemble mean

Rohrer et al. (xxx)

Adds

• Land use bug: additional simulations are available to assess the impact (relevance for extremes such as heat waves)

• CC400: Cyclone analysis• CESM1: 850 -2100 AD cyclone variability

12Blumer et al (2015, in prep.)