Mid-latitude and Tropical Storms Simulated Changes in Atmospheric Drivers of Extreme Sea Levels Ruth...

Mid-latitude and Tropical Storms Simulated Changes in

Atmospheric Drivers of Extreme Sea LevelsRuth McDonald

Hadley Centre, Met Office

Understanding Sea-level Rise and Variability WCRP Workshop, Paris, June 2006

[email protected] Ruth Carnell

© Crown copyright 2005

Outline

Introduction

Model predictions of future changes in the frequency and intensity of mid-latitude storms

Model predictions of future changes in the frequency of tropical storms

Why are cyclones important for sea-level?Storm surges

1953 flooding around North Sea coastHurricane Katrina New Orleans 2005


Introduction to tropical and extra-tropical cyclones

Tropical Cyclone Extra-tropical cyclone

colours = SST blue=15°C, blue/green = 20°C, green =25°C

solid lines = wind speed

Figure from Merrill (1993), downloaded from Hurricanes FAQ by Chris Landsea at http://www.aoml.noaa.gov/hrd/tcfaq/A7.htmlStorm descriptions based on Hurricanes FAQ Section A7 (by Stan Goldenberg)

No temperature contrast at surface

Energy from latent heat

Baroclinic

Energy from horizontal temperature contrast

Contours= pressure surfaces

Warm core

Strongest winds near surface

Cold core

Strongest winds near tropopause

Scale of 100s km Scale of 1000s km


Impacts of global warming on storms

It is often assumed that global warming will cause an increase in the frequency and intensity of extra-tropical and tropical cyclones

Not necessarily the case

Mid-latitude storms Changes occur as a result of competing effects due to changes in atmospheric

temperature and moisture Decrease in low level temperature contrast between pole and equator

Less energy for storms Increases in upper level temperature gradient

More energy for storms Local temperature contrasts are also important More moisture

More latent heating. More intense storms Fewer storms are required to give the same energy flux between equator

and poles

Tropical storms Linked to enhanced sea surface temperatures and increased moisture Changes to large-scale circulation, wind shear

Changes to modes of variability like NAO and ENSO also important


Analysis of storms in climate models

Apply an objective technique to locate and in some studies track storms

Local centres of geopotential height, mean sea level pressure or relative vorticity

Last for at least 2 days and be non-stationary (if tracking)

Tropical cyclones also test for warm cores

Use parameter diagnostics Band pass filter storm track to look at synoptic variability Eady parameter to look at baroclinicity Seasonal genesis parameter for tropical storms

Lots of techniques, makes it hard to compare results


Examples of model cyclone tracks

Tropical Storms for 15 years

Mid-Latitude Storms for a single winter

Organised into tracks: Atlantic, Pacific, Mediterranean

Tracks look sensible, despite low resolution and poor simulation of individual cyclones

Few events

Mid-latitude Storms


Simulation of mid-latitude storms by models:-Cyclone density

AMIP 13 Model MeanERA Difference

Lambert et al. (2002) Climate Dynamics

number of cyclone events per 145,000 km2 accumulated over nine 120 day winter periods for the Northern Hemisphere

Summary• All models have systematic errors in the simulation of cyclone tracks• Cyclones tend to be too weak• Errors often larger than climate change signal

Too many Too few

Too far north


Future changes in mid-latitude storms:-Cyclone and track density

ECHAM5-OM A1B

ECHAM4/ OPYC3 IS92a

Bengtsson et al. (2006) J Climate, in press, thanks to K Hodges

Tracks per month per 106 km2 Leckebusch et al.

(2006)Climate Research,in press, thanks to G Leckebusch

Track density

Carnell and Senior (1998)Climate Dynamics

Cyclones per season per 106 km2

HadCM2 IS92a

JMA

Geng and Sugi (2003)J ClimateCyclones per 4.5°x4.5° per season

North Atlantic

HadAM3P A2 ECHAM5

NE Pacific

SH

Summary: Little consensus of local changes in frequency of storms amongst climate models


Future changes in the frequency of winter mid-latitude storms

Reference Model Experiments NH Change SH Change

Carnell and Senior 1998

HadCM2 N48

IS95a3x30y

Fewer

Geng and Sugi 2003

JMA T106 20yOBS2050s

FewerPoleward and eastward

Fewer

Fyfe 2003 CCCma 3xIS92a 500y Ctrl

Sub-Antarctic 30% fewer

Lambert 2004 CGCM1CGCM2 T32

1%1850-2100

Fewer Fewer

Watterson 2006 CSIROMk2 R21, Mk3 T63

30yA2

Fewer Fewer

Lambert and Fyfe 2006

IPCC 4ARGCMs

20y FewerNo shift

FewerNo shift

Bengtsson et al. 2006

ECHAM5 OM T63

3x30yA1B

No change Poleward shift

No changePoleward shift

Summary: There are fewer mid-latitude storms in winter in both hemispheres in the future simulations


Future changes in the frequency of intense Northern Hemisphere winter mid-latitude storms

Reference Model Experiment Intensity measure

Change in frequency of intense cyclones

Carnell and Senior 1998

HadCM2 N48

IS95a3x30y

Central MSL pressure

More intense

Geng and Sugi 2003

JMA T106 20yOBS, 2050s

Central MSL pressure gradient

More intense

Lambert 2004

CGCM1CGCM2 T32

1%1850-2100

Central MSL pressure

More intense

Watterson 2006

CSIROMk2 R21, Mk3 T63

30yA2

Various dynamical measures & precipitation

Little change in dynamical intensity, more precipitation

Lambert and Fyfe2006

IPCC 4ARGCMs

20y Central MSL pressure

More intense

Bengtsson et al. 2006

ECHAM5 OM T63

3x30yA1B

Central Relative vorticity

Fewer weak

Summary: There is some evidence of an increase in the frequency of the deepest storms in the future simulations


Summary of other studies on changes in mid-latitude storms

Ref Model Exp Changes

Lionello et al. 2002 ECHAM4 30y2xCO2

Fewer tracks in Mediterranean region

Fyfe 2003 CCCma IS92a x31850-2100

Sub-Antarctic fewer cyclones

Lozano et al 2004 ECHAM4 AGCM T106

2xCO2 30y Coastal stormsFewer but more intense in region covering Ireland and Scotland

Leckebusch and Ulbrich 2004

HadCM3 A1, B230y

More North Atlantic cyclone tracks, and more intense

Yin 2005 IPCC 4AR GCMs A1B20y

BPF EKEPoleward and upward shiftintensification

Inatsu and Kimoto 2005

CCSR/NIES/FRCGC AGCM

20y x7 2xCO2 timeslice

EKE shows W Pacific tracks stronger and W Hemisphere track weaker

Fischer-Bruns et al. 2006

ECHAM4- HOPEG T30

A2, B2 Max wind speed events, poleward shift, more N Atl, SO, fewer Pacific ocean

Leckebusch et al. 2006

5 GCMs A1 and IS92a30y

Fewer in N Atlantic, Oct-Mar More intense

Tropical Storms


Simulation of tropical storms by models:- cyclone genesis density

N144 HadAM3

McDonald et al. (2005) Climate Dynamics

Cyclone genesis per 0.83°x1.25° x per 17y

T106 JMA

Yoshimura and Sugi (2006) SOLA

Observations 10y

Model CLIM1 10y

Models simulate cyclones in S Atlantic

Too few in NE Pacific

Summary: Simulation of TC genesis is realistic but there are some errors


Future changes in the frequency of tropical storms

McDonald et al. (2005) Climate Dynamics Cyclone genesis per 0.83°x1.25° x per 17y

N144 HadAM3

Oouchi et al. (2006) J Met Soc Japan

T106 JMA

Sugi et al. J Met Soc Japan

20km MRI/JMA

N AtlanticNW Pacific


Future changes in the frequency of tropical storms

Ocean basin

model reference Global NA WNP ENP NI SI SWPT106 JMA 10y Sugi et al. 2002 66 161 34 33 109 43 69

T42 NCAR CCM2 10y Tsutsui 2002 102 86 111 91 116 124 99

N144 HadAM3 15y McDonald et al. 2005 94 75 70 180 142 110 82

T106 CCSR/NIES/FRCGC

Hasegawa and Emori 2005

96

T106 JMA 10y Yoshimura & Sugi 05 fewer

T63 ECHAM5-OM Bengtsson et al. 2006 94

20km MRI/JMA Oouchi et al. 2006 70 134 62 66 48 72 57

Ratio (%) of number of storms in global warming experiment to number in control experiment

Red = significantly more tropical storms in the future simulationBlue = significantly fewer tropical storms in the future simulation

Summary: fewer tropical cyclones globally in the future simulations, sign of regional changes varies between model and basin


Summary

IPCC TAR: simulated future changes in storms are inconclusive

There are still large uncertainties in the future changes of mid-latitude and tropical storms

Mid-latitude storms Models are tending to agree on there being fewer Northern and

Southern Hemisphere extra-tropical storms in winter Models do not agree on regional changes in frequency of storms Some models show poleward shifts in the storm tracks There is some agreement on increased frequency of extra-tropical

storms with central pressure below 970 hPa

Tropical storms Models are tending to show reduced frequency of tropical storms, but

the sign of the changes varies with region


References

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10.1007/s003820050229 Fischer-Bruns I., von Storch H, Gonzáles-Rouco JF and Zorita E (2005) Modelling the variability of midlatitude storm activity on decadal to century time scales. Clim

Dynam 25: 461 – 476, DOI: 10.1007/s00382-005-0036-1 Fyfe JC (2003) Extratropical Southern Hemisphere cyclones: harbingers of climate change? J Clim 16: 2802-2805, DOI: 10.1175/1520-

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Royal Meteor Soc Hasegawa A and Emori S (2005) Tropical cyclones and associated precipitation over the Western North Pacific: T106 atmospheric GCM simulation for present-day

and doubled CO2 climates. SOLA 1: 145-148, SOI:10.2151/sola.2005-038 Inatsu M, Kimoto M (2005) Two Types of Interannual Variability of the Mid-winter Storm-tracks and their Relationship to Global Warming. SOLA 1: 61-64, DOI:

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Mid-latitude and Tropical Storms Simulated Changes in Atmospheric Drivers of Extreme Sea Levels Ruth...

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