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Global Warming and
Tropical Cyclone Activity
in the western North Pacific/
Thermodynamic Controls on
Intense TCs
Johnny Chan
Guy Carpenter Asia-Pacific Climate Impact Centre
City University of Hong Kong
Outline
• Part I - Actual observations and possible explanations of the variations of the following WNP TC characteristics
– numbers and intensity
– tracks and landfall locations
• Part I Summary
• Part II – relationship between MPI and frequency of occurrence of intense TCs
Part I
Actual observations and explanations
– Number and Intensity
Annual Number of TCs and intense TCs in WNPAnnual 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
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
Sea-surface
Temperature
Anomalies
Period A1
Period B
Period A2
Reconstructed
Moist Static
Energy (EOF2)
Period A1 Period A2
Period B
Vertical Gradient of
Saturated Moist
Static Energy
(1000 minus 600 hPa)
Period A1 Period A2
Period B
Precipitation Rate
Anomalies
Period A1 Period A2
Period B
Lower Tropospheric
Streamfunction
Anomalies
Period A1 Period A2
Period B
200-hPa minus 850-hPa Zonal Wind Shear
Period 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 TyphoonsProceedings, Royal Society A (2008)
Actual observations and explanations
– Track and Landfall Variations
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
Number of Typhoons Making Landfall in Zhejiang
Province of China (East China) Every 5-year period
(1960-2005)
Number of Typhoons Making Landfall in
Guangdong/Hainan (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
EO
Fs 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
EOF1
EOF2
EOF3
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.
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.
Part II
Background
•MPI = f(SST, outflow temperature, net
tropospheric CAPE)
•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
Identify the extent to which the
frequency of occurrence of intense
TCs is controlled by thermodynamic
(versus dynamic) factors by
examining the relationship between
MPI and such a frequency
Objective
Track data
1. Operational datasets
•HURDAT for Atlantic and eastern
North Pacific TCs
•JTWC for the rest
2. Homogeneous dataset from
Kossin et al. (2007)
Data for calculating MPI
NCEP reanalyses
Data
Correlations with MPI
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 with NCat45 - Atlantic
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.