19 October 2005 The CRCES Workshop on Decadal Climate Variability

Modelling the Variability of Midlatitude Storm Activity on

Decadal to Century Time Scales

Hans von Storch, Institute for Coastal Research, GKSSIrene Fischer-Bruns, Max Planck Institute for MeteorologyGermany

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Atmosphere-Ocean GCM ECHO-G

Atmospheric Model ECHAM4 (T30) (~3.75°x 3.75° ~300 km x 300 km)

Ocean Model HOPE-G (T43) (~2.8°x 2.8° ~200 km x 200 km)

Model & Experiments

2 Historical Simulations 1550-1990(time dependent solar / volcanic / GHG forcing)

3 Future Climate Change Simulations (CMIP2, SRES A2/B2) (152 resp. 110 years)

Control Simulation 1000 years

(present day conditions)

19 October 2005 The CRCES Workshop on Decadal Climate Variability

19 October 2005 The CRCES Workshop on Decadal Climate Variability

19 October 2005 The CRCES Workshop on Decadal Climate Variability

The millennial run generates temperature variations considerably larger than MBH-type reconstructions.

The simulated temperature variations are of a similar range as derived from NH summer dendro-data, from terrestrial boreholes and low-frequency proxy data.

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Reconstructed and simulated winter temperature anomalies in eastern China (Liu et al., 2005)

19 October 2005 The CRCES Workshop on Decadal Climate Variability

1675-1710vs. 1550-1800

Reconstruction from historical evidence, from Luterbacher et al.

Late Maunder Minimum

Model-based reconstuction

19 October 2005 The CRCES Workshop on Decadal Climate Variability

IPCC SRES A2 and B2 emissions marker scenarios

• A2Business as usual

External Forcing – Future Scenarios

• B2 Strong focus on environmental protection

Lower emissions –less future warming

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Applications so far• Methodical analysis of performance of MBH method and MM05 “AHS”

mechanism.(von Storch, H., E. Zorita, J. Jones, Y. Dimitriev, F. González-Rouco, and S. Tett, 2004: Reconstructing past climate from noisy data, Science 306, 679-682;von Storch, H., and E. Zorita, 2005: Comment to "Hockey sticks, principal components and spurious significance" by S. McIntyre and R. McKitrick, Geophys. Res. Lett. (in press) doi:10.1029/2005GL022753)

• Simulation of Late Maunder Minimum – regional European or near-global phenomenon(Zorita, E., H. von Storch, F. González-Rouco, U. Cubasch, J. Luterbacher, S. Legutke, I. Fischer-Bruns and U. Schlese, 2004: Climate evolution in the last five centuries simulated by an atmosphere-ocean model: global temperatures, the North Atlantic Oscillation and the Late Maunder Minimum. Meteor. Z. 13, 271-289)

• Comparison with multidecennial Chinese temperatures( 刘 健 , H. von Storch, 陈 星 , E. Zorita, 郑景云 , and 王苏民 , 2005: 千年气候模拟与中国东部温度重建序列的比较研究 (Comparison of simulated and reconstructed temperature in eastern China during the last 1000 years), Chinese Science Bulletin, in press)

• Low frequency variability in temperature modes and Extratropical storminess(Zorita, E., F. González-Rouco, H. von Storch, J.P. Montavez und F. Valero, 2005: Natural and anthropogenic modes of surface temperature variations in the last millennium, Geophys. Res. Letters 32, L08707Fischer-Bruns, I., H. von Storch, F. González-Rouco and E. Zorita, 2005: Modelling the variability of midlatitude storm activity on decadal to century time scales. Clim. Dyn. DOI 10.1007/s00382-005-0036-1)

19 October 2005 The CRCES Workshop on Decadal Climate Variability

North Atlantic Storminess: Observational results

12 hourly pressure changes exceeding 16 hPa / 12hLund

Stock-holm

Worsening of storminess in NAtl since a minimum in the 1960s consistent with NAO changes

No significant changes over last 100 years (WASA, 1998)

Different storm indicators from pressure readings 1780/1820-2000 No evidence of long-term trend (Bärring & von Storch, GRL, 2005.)

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Atmosphere-Ocean GCM ECHO-G

Atmospheric Model ECHAM4 (T30) (~3.75°x 3.75° ~300 km x 300 km)

Ocean Model HOPE-G (T43) (~2.8°x 2.8° ~200 km x 200 km)

Model & Experiments

1 Historical Simulation 1550-19901550-1990(time dependent forcing)(time dependent forcing)

3 Future Climate Change Simulations3 Future Climate Change Simulations (CMIP2, (CMIP2, SRES A2/B2) (152 resp. 110 years)/B2) (152 resp. 110 years)

Control Simulation Control Simulation 1000 years1000 years

(present day conditions)(present day conditions)

19 October 2005 The CRCES Workshop on Decadal Climate Variability

• diagnosed at every grid-point and at every time step • stored every 30 minutes• output every 12 hours

Extreme wind speed events per season ( 8 Bft, gales )

were counted

Simulated data10m maximum wind speed

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Analysis of different model experiments with respect to gale frequency

Determination of simple indicators describing storm activity

Model Study

Storm IntensityIndex

Storm Shift Index

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Mean number of gale days (10m wind speed reaching at least 8 Bft) in the northern winter season DJF (left) and in the southern winter season JJA (right) for the pre-industrial period 1551-1850 in the historical experiment (upper panels) and mean number of storm days (10m wind speed reaching at least 10 Bft, lower panels).

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Mean number of gale days (10m wind speed reaching at least 8 Bft) in the northern winter season DJF (left) and in the southern winter season JJA (right) for the industrially influenced period 1851-1990 in the historical experiment.

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Mean number of gale days (10m wind speed reaching at least 8 Bft) in the northern winter season DJF (left) and in the southern winter season JJA (right) during the last 300 years of the control run of 1000 years length.

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Mean number of gale days (10m wind speed reaching at least 8 Bft) in the northern winter season DJF (left) and in the southern winter season JJA (right) in the A2 climate change experiment.

19 October 2005 The CRCES Workshop on Decadal Climate Variability

industrial – pre-industrial

Storm Intensity

DJF

JJA

A2 – pre-industrial

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Storm Intensity Mean number of gale-days averaged over time and region

NH: no changeSH: increase

pre-ind ind A2

Storm Intensity Index

Storm intensity index

= plain storm count

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Storm Intensity Mean number of galedays averaged over time and region

NH: no changeSH: increase

pre-ind ind A2

N Atl: increase N Pac: decreaseStorm Intensity

Index

pre-ind ind A2

(150E-90W)

(90W-30E)

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Storm Shift

26.5 %

23.4 % NAtl (DJF)

NPac(DJF)

SH(JJA)

11.2 %

Leading EOFs pre-ind Pattern of slope

coefficient in A2

y = -0.18.x + 34.1 -53%

y = 0.20x+20.7 +95%

y = 0.22x + 26.5 + 84%

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Storm Shift

PCs obtained by projection onto EOFEOFs pre-ind

NAtl (DJF)

NPac(DJF)

Storm Shift Index

SH(JJA)

pc1

pc4

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Poleward shift (NE)Intensity: slight increase

Poleward shiftIntensity: decrease

(11-yr running mean)

Temp & Indices:No correlation in pre-industrial period

N Atlantic

Warming and Storms

pc1 pc4

N Atlantic

N Pacific

Warming and Storms

NAtl TempStorm Intensity IndexStorm Shift Indices

NPacTempStorm Intensity IndexStorm Shift Index

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Intensity: sharp increasePoleward shift

Warming and Storms

Southern Hemisphere

SH TempStorm Intensity IndexStorm Shift Index

(11-yr running mean)

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Conclusions – long term simulation

• Historical runs done.• Realistic sequence of warming and

cooling.• Variations larger than in multi-proxy

regression-type reconstructions, but consistent with other reconstructions and some regional data.

Hans von

Storch

19 October 2005 The CRCES Workshop on Decadal Climate Variability

Conclusions - storms

• Analysis of long-term model data with respect to wind speed extremes; Determination of two simple indicators describing storm intensity and storm track location.

• The storm indices show no trends in the historical experiments, except for SH in 20th century.

• NH Temperature and Storm activity are uncorrelated in the pre-industrial period

• Future climate change scenario A2: - Parallel increase of storminess indices and temperatures. - Poleward shift of the region with maximum gale intensity for NAtlantic (NE), NPacific and SH; Storm intensity is constant over the NH as a whole, but increasing in the Atlantic region and decreasing in the Pacific - Increase of storm intensity for SH

Irene Fischer-

Bruns