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

This study examines the impact of climate background, ENSO and MJO on tropical cyclone (TC) activities in the Northwest Pacific Ocean. It analyzes the modulation of TC activities by ENSO and decadal oscillations, as well as the modulation of TC activities by the Madden-Julian Oscillation (MJO). The study also explores the composite TC activities in 2004 in the western North Pacific.

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

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

  2. Outline 1. Climate background-Modulation of TC activities by ENSO & Decadal Oscillations2. Modulation of TC activities by MJO  Composite TC activities in 2004 in the western North Pacific

  3. Climate background 1 Warm minus Cold Warm Cold • Modulation of TC byEl 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.). Wang and Chan (2002) Ho et al. (2005) Camargo and Sobel (2005)

  4. Climate background 2 (1980-2001) - (1951-1979) (1980-2001) - (1951-1979) JJAS (1971-2000) TS+TY (Vmax>17 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) • Modulation of TC by Tropical Pacific multi-decadal variability • ID1 (1951–79) to ID2 (1980–2001)Typhoon passage frequency

  5. Climate background 2 TS+TY (Vmax>17 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. • Modulation of TC by Tropical Pacific multi-decadal variability • Significantly affects the frequency of tropical cyclogenesis (Matsuura et al. 2003).

  6. ENSO High level Decadal Variability Seasonal mean genesis location and tracks cold Low level warm Eq Seasonal mean genesis location

  7. High level Low level warm Eq Decadal Variability Seasonal genesis number Seasonal mean genesis location and tracks General mechanism is similar!

  8. TC-MJO: composite  Modulation of TC by MJO • 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

  9. TC-MJO: composite • # 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  Modulation of TC by MJO Positions of TC geneses (o)

  10. 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. A B C D E D 23 12z A 5 12z B 9 00z E 26 06z C 13 18z

  11. 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).

  12. 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 0 5 3 3 0 0 3 0 3

  13. 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 3 1.75

  14. A B C D E D 23 12z A 5 12z B 9 00z E 26 06z C 13 18z

  15. Total OLR (5N-15N) Black line : MJO Green line : Rossby wave Purple line : MRG wave

  16. 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

  17. 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 ?

  18. Cyclogenesis Mechanism In June 2004 Rossby wave in easterly flow

  19. TC A Warning : 2004/06/04 06UTC @ 15.7N, 116.6E Contour 30-60 OLR Rossby wave in eastery flow TD-type disturbance

  20. TC A Warning : 2004/06/04 06UTC @ 15.7N, 116.6E TC B Warning : 2004/06/05 12UTC @ 6.7N, 141.7E Eastery wave Monsoon confluence zone

  21. TC C Warning : 2004/06/11 18UTC @ 6.4N, 140.0E Rosssby wave energy dispersion B Monsoon shear line

  22. TC D Warning : 2004/06/21 18UTC @ 13.0N, 147.3E MRGW TD-type disturbance

  23. TC E Warning : 2004/06/24 18UTC @ 11.6N, 153.8E TD-type disturbance Monsoon shear line

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