1. Seoul National University
Changes in Tropical-Cyclone Lifetime-Maximum- and landfall- Intensity over the western North Pacific
Doo-Sun Park
Seoul National University 1

2. Notable Increase of SST in the western Pacific
Time series of sea surface temperature
in the western North Pacific
Linear trend of sea surface temperature
during the period 1982‒2010 (ºC decade‒1)
The western North Pacific shows significant increasing tendency of sea surface temperature (SST) during the period
The increase of SST is observed over the almost entire western North Pacific basin.
An increase in tropical cyclone (TC) intensity can be easily expected.
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3. Tropical Cyclone Became Stronger?
These conflicting results mainly come from the different best-track datasets used [Wu et al., 2006; Song et al., 2010].
Thus, in this study, to find consistent trends between the different best-track datasets, regional intensity trends are considered.
The TC intensity and the number of intense TCs show significant increasing trends with tropical ocean warming [Emanuel, 2005; Webster et al., 2005].
decadal variations are more dominant than specific trends [Chan and Liu, 2004; Chan, 2006, 2008].
VS.
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4. Inconsistent Trends among the Best-track Datasets
Time series of average power dissipation index for the period 1977‒2010
(m3 s‒3 hour)
Power Dissipation Index (PDI) [Emanuel, 2005].
Vmax: maximum wind speed
t: total lifetime of tropical cyclone
Year
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5. Tropical Cyclone Became Stronger?
These conflicting results mainly come from the different best-track datasets used [Wu et al., 2006; Song et al., 2010].
Thus, in this study, to find consistent trends between the different best-track datasets, regional intensity trends are considered.
The TC intensity and the number of intense TCs show significant increasing trends with tropical ocean warming [Emanuel, 2005; Webster et al., 2005].
decadal variations are more dominant than specific trends [Chan and Liu, 2004; Chan, 2006, 2008].
VS.
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6. Grid Analysis
A 5º square box was set up, and average of intensity and occurrence of lifetime maximum intensity were calculated in the box.
By shifting the box at a 1° interval in latitude and longitude (far less than the size of the window), gridded data with a 1º horizontal resolution were constructed,
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7. Best-track Datasets
RSMC
JTWC
HKO
CMASTI
Record period
1951‒present
1945‒present
1961‒present
1949‒present
Sustained time
10 minutes
1 minute
2 minute
Multiplicative
factor ‒
0.88
[Knapp and Kruk, 2010]
0.871
Time interval of
record
6 hours
(3 hours
near Japan)
Unit
Knot
m s ‒1
In this study, all available best-track datasets were utilized.
Some differences among the datasets were standardized.
The analyses were confined to the period 1977–2010.
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8. Tropical Cyclone Intensity Change
Contour: averages of trends
Color shades: number of datasets that showing statistically significant trend
Dots: All datasets represent same signs of trends
Consistent intensity increase in the subtropical and mid-latitude ocean while consistent decrease in the tropical ocean.
(m s‒1 decade‒1)
(m s‒1 decade‒1)
Mean
UW/NCDC
RSMC
JTWC
HKO
STI SJ
+0.97
+1.39*
+0.64
+1.54*
+1.05
+0.66 TP
‒2.35*
‒0.81
‒2.28*
‒2.00*
‒2.75*
‒2.36*
* denotes that the trend is statistically significant at the 90% confidence levels.
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9. Change of Location of Maximum Wind Occurrence
Contours: climatological distribution
Colors: averages of trends
Dots: three of datasets show statistically significant trends
The location of maximum wind occurrence has been shifted toward the East Asian continent.
This can make stronger tropical cyclones strike the East Asia if maximum intensity does not weaken.
(decade‒1)
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10. Changes of Maximum and Landfall Intensity
(m s‒1 decade‒1), asterisks indicates the trend is statistically significant at the 95% levels
RSMC
JTWC
HKO
STI UW
/NCDC
East Asia
Maximum intensity
before landfall
−0.04
+2.42*
−0.77
−0.62
+0.01
Landfall intensity
+0.58
+1.81*
+0.92
+0.79*
+0.56
Linear trends of TC maximum intensity do not represent notable decreasing tendencies.
Thus, because the maximum wind occurrence has approached East Asia and its intensity rarely changed, much more intense TCs can strike East Asia during a recent decade. All of the TC datasets display consistent positive trends.
However, some of them are not statistically significant at the 95% confidence levels. This may be because of the genesis shift.
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11. Changes of Genesis Location
Contours: climatological distribution
Colors: averages of trends
Dots: three of datasets show statistically significant trends
The increase of genesis over the northern South China Sea may be a factor to reduce maximum intensity due to the shortened lifetime over ocean.
(decade‒1)
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12. Changes of Intensification Rate
Contour: averages of trends
Color shades: number of datasets that showing statistically significant trend
Dots: All datasets represent same signs of trends
Although genesis location shifted toward land, enhanced intensification rate could rapidly strengthen TC and help TC to sustain its intensity longer.
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13. Changes of Maximum and Landfall Intensity
(m s‒1 decade‒1), asterisks indicates the trend is statistically significant at the 95% levels
RSMC
JTWC
HKO
STI UW
/NCDC
Southeast Asia
Maximum intensity
−1.22
−0.51
−2.16*
−1.56*
−0.99
Landfall intensity
−0.43
+0.63
−0.45
+0.08
−0.40
Northeast Asia
+0.24
+3.55*
+0.45
−0.54
+0.52
+1.29*
+2.35*
+2.04*
+1.01*
+1.43*
Here, we divide East Asia into Northeast and Southeast Asia based on 25˚N.
In the Southeast Asia where main genesis region is very close, the shifted genesis location may strongly affect the maximum intensity, but not in the Northeast Asia.
In Southeast Asia, the maximum intensity trends are consistently negative although they are not significant. Otherwise, the landfall intensity trends are less negative or even slightly positive.
In the Northeast Asia, there are no significant negative trends in maximum intensity. However, all of the landfall intensity trends are significantly positive.
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14. Recent Changes of Thermodynamic and Dynamic Conditions
(ºC decade‒1)
(m s‒1 decade‒1)
Along the coastal seas
The east of the Philippine Sea
Thermodynamic condition
Favorable
Weakly Favorable
Dynamic condition
Unfavorable
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15. Tropical Convection and Wave Propagation
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16. Model results: Tropical Convection and Wave Propagation
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17. Summary : Recent maximum wind occurrence : Old maximum wind occurrence
Favorable
Unfavorable
La-Nina-like warming  Enhanced Walker Circulation & PNA-like wave propagation  Changing Dynamic Conditions within the basin.
More TCs reach their maximum intensity closer to the East Asian continent, which leads to stronger landfall intensity, particularly, over the Northeast Asia.
Over the Southeast Asia, because of genesis effect, landfall intensity has not been intensified.
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18. Thank you
Park, D.-S. R., C.-H. Ho, J.-H. Kim*, and H.-S. Kim (2013) Spatially inhomogeneous trends of tropical cyclone intensity over the western North Pacific for 1977‒2010, Journal of Climate, 26, 5088–5101, doi:
Park, D.-S. R., C.-H. Ho*, and J.-H. Kim (2014) Growing threat of intense tropical cyclones to East Asia over the period 1977–2010, Environmental Research Letters, 9, , doi: / /9/1/ [Research highlight in Nature on 23 Jan Climate change: Strong storms shift landwards, Nature, 505, 457, doi: /505457c].
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