possible effects of global warming on tropical cyclone

Possible Effects of Global Warming on Tropical Cyclone Activity

Johnny ChanGuy Carpenter Asia-Pacific Climate Impact Centre

City University of Hong Kong

1Guy Carpenter Asia-Pacific Climate Impact Centre, City University of Hong Kong

Outline

Background

Relationship between global warming and

frequency of intense tropical cyclone

occurrence

Variations of tropical cyclone

characteristics in the western North

Pacific

Summary


Background

Global warming leads to

– an increase in the temperature near the earth’s

surface (land and ocean)

– an increase in the amount of water vapour in the

atmosphere due to an increase in ocean temperature

and a higher atmospheric temperature capable of

holding more water vapour

No study has definitively demonstrated that the

dynamic factors are modified by global warming

(although some have suggested an increase in

vertical wind shear).


Background

Due to global warming, the thermodynamic

factors have become more favourable for

tropical cyclone formation and development.

To determine whether global warming has an

impact on the frequency of occurrence of

tropical cyclones or of intense cyclones, we

need to examine whether the thermodynamic

factors are related to the variations on such

frequencies.

A good proxy of the thermodynamic factors is

the Maximum Potential Intensity (MPI)


•MPI = f(ocean temperature, outflow temperature, net

amount of energy available for convection)

•Because MPI gives the maximum possible intensity, a

higher value of MPI summed over the ocean basin and

over a season should imply a more thermodynamically

energetic atmosphere, and more TCs could reach

higher intensities

a season with a higher value of MPI

should have more intense TCs if the

dominant control is thermodynamic

Background


Atlantic

0

1

2

3

4

5

6

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

Nu

mb

er

of

Cat4

5

54

56

58

60

62

64

66

68

MP

I

Cat45

NCEP MPI


Western North Pacific

0

2

4

6

8

10

12

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

Cat4

5

60

62

64

66

68

70

72

74

MP

I

Jul-Nov Cat45

NCEP MPI


21-year running correlations with NCat45

Ocean Basin Period Correlation

(best track)

Correlation

(Kossin et al. 2007)

Atlantic 1960-2007 0.45

1970-2007 0.59

1980-2007 0.63

1979-2006 0.61 0.61

Western North Pacific 1960-2007 -0.01

1970-2007 -0.06

1980-2007 -0.08

1981-2006 -0.13 -0.36

Eastern North Pacific 1960-2007 0.29

1970-2007 0.35

1980-2007 0.34

South Indian Ocean 1981-2007 0.35

South Pacific 1981-2007 0.03


21-year running correlations of MPI with NCat45

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1980 1985 1990 1995 2000 2005

Atlantic WNP ENP

21-year running correlations with NCat45


21-year running correlations with Atlantic NCat45

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1980 1985 1990 1995 2000 2005

MPI CAPE T0 SST

21-year running correlations with NCat45 - Atlantic


21-year running correlations with ENP NCat45

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

1980 1985 1990 1995 2000 2005

MPI CAPE T0 SST

21-year running correlations with NCat45 - ENP


21-year running correlations with WNP NCat45

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

1980 1985 1990 1995 2000 2005

MPI CAPE T0 SST

21-year running correlations with NCat45 - WNP


Summary

Thermodynamic control on the frequency

of intense TCs is important only in the

Atlantic

Estimating the effect of global warming on

the frequency of intense TCs therefore

must also assess such an effect on the

dynamic processes.


Western North PacificTropical Cyclones


Number and Intensity


Annual number of TSs and Cat45 TCs over the WNP

15

20

25

30

35

40

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

0

2

4

6

8

10

12

14

TS

10-yr filtered TS

Cat45

10-yr filtered Cat45

Annual Number of TCs and Intense TCs in the WNP


Webster et al.’s (2005) Science paper


1975-89 1990-2004

Number 75 115

Percentage 32 42

No. of Category 4 and 5 Typhoons


1960-74 1975-89 1990-2004

Number 105 75 115

Percentage 37 32 42

No. of Category 4 and 5 Typhoons


ACE vs.. VORT, SHEAR and MSE

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

ACE

VORT EOF1

SHEAR EOF1

MSE EOF2

0.580.72 0.67

Science, 311, 1713b, Tellus 2007


Wavelet Analysis of Intense Typhoon Occurrence Frequency

2-7 yr

16-32 yr

Period A1 Period B Period A2


Ocean

Temperature

Anomalies

Period A1

Period B

Period A2


Saturated Moist

Static Energy

Anomalies

Period A1 Period A2

Period B


Anomalies of Vertical

Gradient (1000 minus

600 hPa) of Moist

Static Energy

Period A1 Period A2

Period B


Rainfall Anomalies

Period A1 Period A2

Period B


Vertical Wind ShearPeriod A1 minus Period B Period A2 minus Period B


Frequency of

Occurrence of Intense

Typhoons

Period A1 Period A2

Period B


Blue shading: 95% Green shading: 90%

Period A1 minus Period B Period A2 minus Period B

Difference in the Frequency of Occurrence of Intense Typhoons

Proceedings, Royal Society A (2008)


Track and Landfall Variations


No. of TCs Making Landfall in Japan and Korea Every 5-year period (1970-2004)

No. of Tropical Cyclones Making Landfall in Japan and Korea

0

5

10

15

20

25

30

1970-74 1975-79 1980-84 1985-89 1990-94 1995-99 2000-04

Year

Nu

mb

er


No. of Typhoons Making Landfall in East China Every 5-year period (1960-2005)


No. of Typhoons Making Landfall in South China Every 5-year period (1960-2005)


Variations of Landfall in Each Area at Various Oscillation PeriodsSTC

-3

-2

-1

0

1

2

3

4

1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

Year

Standa

rdized

anoma

lies

-1.5

-1

-0.5

0

0.5

1

1.5

2

Standardized anomalies

original

2-8 yr

8-16 yr

16-32 yr

sta

nd

ard

ize

d a

no

ma

lie

ss

tan

da

rdiz

ed

an

om

alie

s

MTC

-3

-2

-1

0

1

2

3

4

1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

Year

Stand

ardize

d ano

malies

-1.5

-1

-0.5

0

0.5

1

1.5

2

Standardized anomalies

original

2-8 yr

8-16 yr

16-32 yr

sta

nd

ard

ize

d a

no

ma

lies

sta

nd

ard

ize

d a

no

ma

lies

sta

nd

ard

ize

d a

no

ma

lie

ss

tan

da

rdiz

ed

an

om

ali

es

South China, Philippines and

Vietnam

East China

Japan/Korea


Patt

ern

s o

f T

C o

ccu

rren

ce a

no

mali

es

TC

occu

rren

ce a

no

malie

s1977-88

1964-76

1989-97

Pattern 1

Pattern 2

Pattern 3


SummaryNo significant trend in any of the TC

characteristics (number, intensity, track

types, landfall locations) can be identified.

In other words, TC activity in the western

North Pacific does not follow the trend in

the global increase in atmospheric or sea-

surface temperature.

Instead, all such characteristics go

through large interannual and interdecadal

variations.


Summary

Such variations are very much related and

apparently caused by similar variations in the

planetary-scale atmospheric and oceanographic

features that also do not have the same trend as

the global increase in air temperature

Unless the temporal variations of such features

become linear, these TC characteristics are not

expected to vary linearly with time.


Summary

Even if the observed global warming

has an effect, it is probably in the

noise level relative to the large

interdecadal variations and therefore

is not detectable.

possible effects of global warming on tropical cyclone

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