International Workshop on Advancement of Typhoon Track Forecast Technique (Nov. 30-Dec. 2, 2009)1 / 21

Satoru YOKOI1, Y. N. TAKAYABU1,2, J. C. L. CHAN3

1: CCSR, University of Tokyo, Japan 2: JAMSTEC, Japan, 3: City U. Hong Kong, China

Tropical cyclogenesis frequency simulated by

CMIP3 climate models and multi-model based

future projection

International Workshop on Advancement of Typhoon Track Forecast Technique

(December 2, 2009)

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Our project (S-5-2)

Leader: Prof. Yukari N. Takayabu (CCSR, U. Tokyo)

Organizations: U. Tokyo, MRI, JAMSTEC, Nagoya U., Hokkaido U., & Tsukuba U

Target phenomena:

Heating profile due to tropical convection

Tropical cyclone

Madden-Julian oscillation

Asian monsoon seasonal cycle

Silk road pattern

Pacific-Japan pattern

ENSO

Decadal variability

Evaluations of CMIP3 Model Performances for Various Phenomena in the Atmosphere and Oceans, in the

Present-Day Climate and in Future Projections

Exercise using CMIP3 archive

Rush intoCMIP5 analysis

Mean field

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Introduction

How would global warming impact tropical cyclone (TC) characteristics?(frequency, track, intensity, etc.)

Many researchers discussed

global or ocean-basin scale frequency projection

with the use of their own sophisticated high-resolution GCM.

Most recent studies projected decrease trend of global TC number. (e.g. Sugi et al. 2002; McDonald et al. 2005; Oouchi et al. 2006; Bengtsson et al. 2007)

Multi-model based approach will be essential.

• How about regional trends?

- TCs generated at different places tend to affect different countries.

- Inter-model difference should be serious problem.

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CMIP3 multi-model archive

CMIP3: 3rd phase of Coupled Model Intercomparison Project

Outputs of CGCM experiments designed for IPCC AR4.

Strong point: large number of samples

• 24 CGCMs

• 12 series of experiments (20th-century climate, SRES A1B, A2, and B1, etc.)

• Long-term daily-mean outputs (dozens of years for each experiment)

Weak point: Relatively coarse horizontal resolution

• T106 at the utmost.

• TC intensity is hardly simulated, but its frequency seems to be possible.

It is necessary to confirm model performance in simulating TC genesis distribution.

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Objective

To analyze CMIP3 archives to assess global warming impact on TC genesis over the western North Pacific.

Evaluation of model performance in simulating the genesis distribution.

Multi-model based projection.

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Models

12 models (among 24 CMIP3 models)

Horizontal resolution of the atmospheric component is T42 (~300 km) or greater.

Daily-mean outputs are archived at the CMIP3 database.

Model name Country Atmospheric resolution

BCCR-BCM2.0 Norway T63 with “reduced” Gaussian grid equivalent to T42

CGCM3.1(T63) Canada T63 with “reduced” Gaussian grid equivalent to T42

CNRM-CM3.0 France T63 with “reduced” Gaussian grid equivalent to T42

CSIRO-Mk3.0 Australia T63

CSIRO-Mk3.5 Australia T63

ECHAM5/MPI-OM Germany T63

FGOALS-g1.0 China 2.8 deg. Lat. × 2.8 deg. Long.

GFDL-CM2.0 U.S.A. 2.0 deg. Lat. × 2.5 deg. Long.

GFDL-CM2.1 U.S.A. 2.0 deg. Lat. × 2.5 deg. Long.

INGV-SXG Italy T106

MIROC3.2(hires) Japan T106

MRI-CGCM2.3.2 Japan T42

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Definition of TC-like disturbance

(1) 850-hPa relative vorticity (850) local maximum (=TC center) t. (cyclonic vortex)

(2) (300-hPa temperature (T300) at the center)(environmental T300) Tt. (warm core)

(3) Conditions 1 & 2 are satisfied at least 2 time steps.

(4) Genesis point is over the ocean.

(5) At genesis time, maximum wind speed is greater at the 850-hPa level than at the 300-hPa level.

(exclusion of extra-tropical cyclones)

Thresholds (t, Tt) are determined independently for each model.

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Evaluation of model performance- 20th-century experiment -

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Annual TC genesis (20th-Century experiment)

Taylor (2001) diagram

0.642 0.780 0.492

0.740 0.754 0.409

0.350 0.025 0.742

0.033 0.678 0.526

[(5Lat.5Lon)-1(10yrs)-1] Yokoi, Takayabu, Chan (2009, Clim. Dyn.)

Model simulations Observation

T63 with “linear” reduced Gaussian grid

T63 T63

T63

T106

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Seasonal march

Overall winter-to-summer contrast is well reproduced.

i

k

Observation

- High performance models only

- 120-150E mean

Yokoi, Takayabu, Chan (2009, Clim. Dyn.)

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Monsoon trough

May-Jun.

Jul.-Sep.

Model (example)Observation

Tone: 850 Vector: vertical shear

Simulated monsoon trough located to the north of the observation.

Biases in TC frequency seasonal marchYokoi, Takayabu, Chan (2009, Clim. Dyn.)

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Seasonal migration of monsoon trough

Monsoon trough migrates northward during April–August, and retreats southward during August–December.

The trough simulated by five star models migrate northward too fast in early summer, and reaches too north during mature summer.

850-hPa relative vorticity in 120–150E

Observation

Yokoi, Takayabu, Chan (2009, Clim. Dyn.)

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Multi-model based projection

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20C3M and SRES

We compare the cyclogenesis frequency between 20C3M and average of three SRES experiments.

20C climate simulation (20C3M): 40-yr length.

SRES A1B, A2, and B1 experiments: 80-160-yr length.

Model name

20C3M SRESA1B SRESA2 SRESB1

T1961-2000

2046-2065

2081-2100

2181-2200

2046-2065

2081-2100

2046-2065

2081-2100

2181-2200

CGCM3.1(T63) x x x x x x x 3.2

CSIRO-Mk3.0 x x x x x x x x x 1.9

CSIRO-Mk3.5 x x x x x x x x 2.9

ECHAM5/MPI-OM x x x x x x 2.9

INGV-SXG x x x x x 2.9

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Future projection (TC frequency)

ALL 5 models project

increase trends over central North Pacific (CNP), and

decrease trends over the South China Sea (SCS) and areas to the north and east of Philippines.

20th-century experiment

(5-model ensemble)

Projected trends

( [SRES A1B/A2/B1] – [20C3M] )

Yellow （ blue ） tone: all 5 models project increase （ decrease ） trends.

Yokoi, Takayabu (2009, J. Meteor. Soc. Japan)

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Comparison with ENSO signals

Reasons for the increase trends can be discussed by analogy with El Nino situation.

Eastward extension and intensification of monsoon trough is essential.

TC genesis anomaly in El Nino yearsGW impact on SST

Yokoi, Takayabu (2009, J. Meteor. Soc. Japan)

850-hPa relative vorticity (JASON)

1982-2001

ENSO signal

GW impact

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Yokoi, Takayabu (2009, J. Meteor. Soc. Japan)

Decrease trend in and around the South China Sea

Environmental conditions would become more favorable for cyclogenesis, or not show significant change.

Low-level vorticity, vertical wind shear, SST, mid-level humidity.

Observed interannual variability of cyclogenesis is not correlate significantly with ENSO signals.

Projected trends in environmental fieldsProjected trends in

cyclogenesis frequency

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Activity in tropical depression-type disturbances (TDDs)

TDD activity: 3-5-day meridional wind at 850-hPa (Takayabu and Nitta 1993).

An TDD active area is realistically simulated.

The activity would decrease significantly over the SCS and to its southeast.

Observed IAV exhibits similar pattern, implying that weakening trends of TDD activity may play a role in decrease trends in cyclogenesis.

Observation

20C3M

Projected trends

Obs. IAV associated with cyclogenesis over the SCS

Yokoi, Takayabu (2009, J. Meteor. Soc. Japan)

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Projected trends in genesis potential

Models realistically simulate horizontal pattern of GP.

GP does not represent east-west contrast in projected cyclogenesis frequency trends.

GP indices proposed by other papers (e.g. Royer et al. 1998; Caron and Jones 2008) project in the same manner.

20C3M (Contour) & Obs. (shade)

Projected trends

Yellow (pale blue) tones: at least 4 models project increase (decrease) trends.

3

700

3

pot

2

200850

5.1

8505

50

70

V

1.01

110GP

H

uu

Emanuel and Nolan (2004) genesis potential:

850: 850-hPa absolute vorticity

|u850-u200|: vertical wind shear

Vpot: potential intensity (Bister & Emanuel 2002)

H700: 700-hPa relative humidity

Yokoi, Takayabu (2009, J. Meteor. Soc. Japan)

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Summary

Five CMIP3 models realistically simulate horizontal distribution in tropical cyclogenesis over the western North Pacific.

ALL of the five models project increase trends of cyclogenesis over the central North Pacific and decrease trends over the South China Sea and regions east of Philippines.

The former increase trends are primarily attributable to projected eastward extension and intensification of the monsoon trough.

The latter decrease trends are associated with weakening trends in activity of tropical depression-type disturbances.

References:

Yokoi, Takayabu, and Chan (2009, Climate Dynamics, 33, 665–683)

Yokoi, and Takayabu (2009, Journal of the Meteorological Society of Japan, 87, 525-538.

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Future research

Trends in occurrence frequency

Is it completely explained by trends in genesis frequency?

Improvement of genesis potential index to make it applicable to global warming problem.