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Global Warming and
Tropical Cyclone Activity
in the western North Pacific
Johnny Chan
Guy Carpenter Asia-Pacific Climate Impact Centre
City University of Hong Kong
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Outline
• The common perception
• Actual observations and possible
explanations of the variations of
the following TC characteristics
– numbers and intensity
– tracks and landfall locations
• Summary
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The “Common” Perception
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SST increase
•Provides more moisture
•Destabilizes the lower atmosphere
More convection
Increase in TC number and intensity
Global increase in air temperature
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Emanuel’s (2005) Nature paper
PDI: (max wind)3W. North Pacific
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Webster et al.’s (2005) Science paper
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Number of Tropical Cyclones Making Landfall in Japan
0
2
4
6
8
10
12
1960 1965 1970 1975 1980 1985 1990 1995 2000
Year
Nu
mb
er
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Number of Tropical Cyclones 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
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The “Common” Conclusion
Tropical cyclone activity and that
of intense typhoons in the
western North Pacific, as well as
the number of tropical cyclones
making landfall along the Asian
coast have been on the increase
as a result of global warming.
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Actual observations and explanations
– Number and Intensity
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Number of TCs in WNP (from JTWC)
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Number of Typhoons Making Landfall in
Guangdong/Hainan (South China)
Every 5-year period (1960-2005)
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ACE vs. May-Nov SSTA (5-30ON, 120-180OE)
[standardized = (raw-mean)/S.D.]
-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
SSTA
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Webster et al.’s (2005) Science paper
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ACE vs. May-Nov SSTA (5-30ON, 120-180OE)
[standardized = (raw-mean)/S.D.]
-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
SSTA
correlation = -0.30
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1975-89 1990-2004
Number 75 115
Percentage 32 42
No. of Category 4 and 5 Typhoons
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1960-74 1975-89 1990-2004
Number 105 75 115
Percentage 37 32 42
No. of Category 4 and 5 Typhoons
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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
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ACE vs. May-Nov SSTA (5-30oN, 120-180oE)
[10-year Gaussian-filtered; standardized]
-1.5
-1
-0.5
0
0.5
1
1.5
1964 1969 1974 1979 1984 1989 1994 1999
ACE
SSTA
correlation = 0.23
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-1.5
-1
-0.5
0
0.5
1
1.5
1964 1969 1974 1979 1984 1989 1994 1999
ACE
SSTA
correlation = 0.87
ACE vs. May-Nov SSTA (5-30oN, 120-180oE)
[10-year Gaussian-filtered; standardized]
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Wavelet Analysis of Intense Typhoon Occurrence Frequency
2-7 yr
16-32 yr
Period A1 Period B Period A2
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Frequency of
Occurrence of
Intense Typhoons
Period A1 Period A2
Period B
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Blue shading: 95% Green shading: 90%
Period A1 minus Period B Period A2 minus Period B
Difference in the Frequency of Occurrence
of Intense TyphoonsProceedings, Royal Society A (2008)
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Actual observations and explanations
– Track and Landfall Variations
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1964-76 1977-88
1989-97
Anomalies of
Frequency of
TC Occurrence
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TS occurrence PC1
-20
-15
-10
-5
0
5
10
15
20
1964 1969 1974 1979 1984 1989 1994 1999
EOF1 of
10-year-filtered
TC occurrence
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TS occurrence PC2
-15
-10
-5
0
5
10
15
20
25
1964 1969 1974 1979 1984 1989 1994 1999
EOF2 of
10-year-filtered
TC occurrence
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TS occurrence PC3
-15
-10
-5
0
5
10
15
20
1964 1969 1974 1979 1984 1989 1994 1999
EOF3 of
10-year-filtered
TC occurrence
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TS occurrence PC3
-15
-10
-5
0
5
10
15
20
1964 1969 1974 1979 1984 1989 1994 1999
Time series of EOFs of 10-year-filtered TC occurrenceTS occurrence PC1
-20
-15
-10
-5
0
5
10
15
20
1964 1969 1974 1979 1984 1989 1994 1999
TS occurrence PC2
-15
-10
-5
0
5
10
15
20
25
1964 1969 1974 1979 1984 1989 1994 1999
EOF1
(25.8%)
EOF2
(18.0%)
EOF3
(15.2%)
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500-hPa zonal flow
pattern (1977-88)
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500-hPa zonal flow
pattern (1989-97)J Climate (Sept 2008)
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Frequency of Tropical Cyclone Occurrence
NTC
MTC
STC
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south Asia TCs
(STC)
TCs making landfall in south China,
Vietnam and the Philippines
middle Asia TCs
(MTC)
TCs making landfall in East China
(Taiwan, Fujian, Zhejiang and Jiangsu
provinces, and City of Shanghai)
north Asia TCs
(NTC)
TCs making landfall in the Korean
Peninsula and Japan
Asian TCs (ATC)All TCs making landfall anywhere in
East Asia
Landfall Groupings [all tropical cyclones (TCs)
with maximum winds at landfall > 17 m s-1]
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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 Asia
East China
Japan/Korea
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TC Landfalling Frequency (16-32 year period)
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
Year
sta
nd
ard
ize
d a
no
ma
lie
s
STC
MTC
NTC
ATC
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Landfall in East Asia vs. TC Activity over the Western North Pacific
at the 16-32-year Oscillation Period
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000
Year
sta
nd
ard
ize
d a
no
ma
lie
s
STC
MTC
NTC
ATC
TTC
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Summary
• No 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.
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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.
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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.