ChungHsiung Sui1,2

1
Variations of Tropical Cyclones in Relation to
Intra-Seasonal Oscillations over the Northwest
Pacific Ocean

• Chung-Hsiung Sui1,2
• Lin Ching1
• Ming-Jen Yang1,2
• Joo-Hong Kim3
• 1Department of Atmospheric Sciences, National
  Central University, Taiwan
• 2Institute of Hydrological and Oceanic Science,
  National Central University, Taiwan
• 3Met Office Hadley Centre, UK

2
Outline

• 1. Climate background-Modulation of TC
  activities by ENSO Decadal Oscillations
  2. Modulation of TC activities by MJO ?
  Composite? TC activities in 2004 in the
  western North Pacific

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Climate background
1

• Modulation of TC by El Niño and Southern
  Oscillation (ENSO)
• significantly affects the seasonal mean genesis
  location (Lander 1994 Chan 2000 Wang and Chan
  2002 etc.), tracks (Wang and Chan 2002 Ho et
  al. 2005), mean lifetime and intensity (Wang and
  Chan 2002 Camargo and Sobel 2005 Chen et al.
  2006), and landfall (Saunders et al. 2000 Wu et
  al. 2004 Fudeyasu et al. 2006), but does not
  have a clear relationship with the mean genesis
  frequency (Chan 1985 Dong 1988 Wu and Lau 1992
  Lander 1994 etc.).

Warm minus Cold
Warm
Cold
4
Climate background
2

• Modulation of TC by Tropical Pacific
  multi-decadal variability
• ID1 (195179) to ID2 (19802001)
  Typhoon passage frequency

JJAS (1971-2000)
TSTY (Vmax17 m/s)
Typhoon formation frequency
80 tropical cyclones (TC) with Vmax exceeding
17.3 m/s are annually generatedd over the globe
(Gray 1979). 1/3 of all TCs over the globe
occur in the WNP (27.2 during 1971-2000)
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Climate background
2

• Modulation of TC by Tropical Pacific
  multi-decadal variability
• Significantly affects the frequency of tropical
  cyclogenesis
• (Matsuura et al. 2003).

TSTY (Vmax17 m/s)
The interdecadal variability of TC activity in
the WNP correlates with long-term variations in
SST in the tropical central Pacific and with the
monsoon trough that appears over the tropical WNP
during the typhoon season of July to October. The
westerly wind anomalies at near 10N show positive
feedback with the SSTA in the central Pacific.
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ENSO
High level
Decadal Variability Seasonal mean genesis
location and tracks
Low level
cold
warm
Eq
Seasonal mean genesis location
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Decadal Variability
Seasonal genesis number Seasonal mean genesis
location and tracks
General mechanism is similar!
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? Modulation of TC by MJO
TC-MJO composite

• Gray (1979), Nakazawa (1986), Liebmann et al.
  (1994), Sobel and Maloney 2000 Hartmann and
  Maloney 2001 Maloney and Hartmann 2001 Aiyyer
  and Molinari 2003 Maloney and Dickinson 2003).
• the barotropic wave accumulation, from the mean
  flow to the eddy kinetic energy, during MJO
  westerly phase.

• The modulation is more evident in East Pacific
  than in west Pacific

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? Modulation of TC by MJO
TC-MJO composite

• Positions of TC geneses (o)

• of TCs increases significantly in June-July
  from B to C, but not so in Aug-Sept likely due to
  other modulation factors
• The genesis locations modulated by the
  heating-induced circulation.
• The MJO modulate TC tracks so when the MJO
  convection center is found in the equatorial
  Indian Ocean (the tropical WNP), a portion of
  tracks migrates eastward (westward).
• A statistical analysis of TC landfalls by MJO
  category a robust and significant modulation in
  the number of TC landfalls is observed in south
  China, Korea, and Japan, the modulation is
  marginal in the remaining four subareas.

• Category
• A
• B
• C
• D

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June 2004 vs Climate
A record-breaking five tropical cyclones (TC)
formed in the northwestern Pacific (NWP) Ocean in
June 2004 (climatological value 1.8) and two of
them made landfall over Japan. In this study, we
analyze the weather and climate oscillations of
this particular month in relation to other years
from 1982 to 2006 to investigate the possible
causes of this unusual event.
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Table 1. Numbers of Western North Pacific
Tropical Cyclones in June. Red (blue) boxes
represent ENSO warm (cold) years based on Oceanic
Niño Index (ONI). The TC numbers in red
represent TC-active years (more than 3 TCs
occur). Those for TC-inactive years (no TC) are
denoted in blue. The average number of TC in
June from 1982 to 2006 is 1.8. The MJO-active
and inactive June are marked act in red and
inact in blue along with measures of MJO
strength (numbers below) based on RMM indices,
i.e. the summation of amplitude of active phase
(5, 6, 7) or inactive phase (1, 2, 3) in June
larger than 2/3 of mean MJO amplitude in June
(19.58).
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TC tends to be more active in El Niño developing
June and suppressed in La Niña.
1994
2006
2004
1991
2002
1988
TC-active years 1982, 1990, 1997, 2002,
2004 TC-inactive years 1996, 1998, 2000,
2005 Normal years 1983, 1984, 1985, 1986,
1987, 1988, 1989, 1991, 1992, 1993, 1994, 1995,
1999, 2001, 2003, 2006
1987
2000
1999
1998
1984
1997
1983
1995
1982
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TC-active years 1982, 1990, 1997, 2002,
2004 TC-inactive years 1996, 1998, 2000,
2005 Normal years 1983, 1984, 1985, 1986, 1987,
1988, 1989, 1991, 1992, 1993, 1994, 1995, 1999,
2001, 2003, 2006 Typical El Niño 1982, 1987,
1991, 1997 El Niño Modoki 1994, 2002, 2004, 2006
1.8
3.4
5
0
2.25
1.75
3
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(No Transcript)
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Total OLR (5N-15N) Black line MJO Green line
Rossby wave Purple line MRG wave
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Easterly wave ? TD-type disturbance
MJO cyclonic shear zone
Rossby wave
A, B ?Rossby wave energy dispersion
MRGW ? TD-type disturbance
TD-type disturbance
Monsoon cyclonic shear zone
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Summary and Discussions

• TC activities (genesis, track, intensity)
  modulated by ENSO and decadal scale oscillations,
  through SST, circulation, and heating
• MJO modulation in summer monsoon season
  relatively weaker , through heating
• The large-scale modulation in June is more
  evident due to the state of June in season
  transition
• TC genesis in June 2004 is a combined result of
  favorable large-scale environment provided by a
  developing El Niño warming condition and a MJO
• Effect of TC on intraseaonal oscillations ?

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Cyclogenesis Mechanism In June 2004
Rossby wave in easterly flow
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TC A Warning 2004/06/04 06UTC _at_ 15.7N, 116.6E
Contour 30-60 OLR
Rossby wave in eastery flow
TD-type disturbance
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TC B Warning 2004/06/05 12UTC _at_ 6.7N, 141.7E
TC A Warning 2004/06/04 06UTC _at_ 15.7N, 116.6E
Eastery wave
Monsoon confluence zone
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TC C Warning 2004/06/11 18UTC _at_ 6.4N, 140.0E
Rosssby wave energy dispersion
Monsoon shear line
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TC D Warning 2004/06/21 18UTC _at_ 13.0N, 147.3E
MRGW
TD-type disturbance
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TC E Warning 2004/06/24 18UTC _at_ 11.6N, 153.8E
TD-type disturbance
Monsoon shear line