Variations of Tropical Cyclones in Relation to IntraSeasonal

Variations of Tropical Cyclones in Relation to Intra-Seasonal Oscillations over the Northwest Pacific Ocean Chung-Hsiung Sui 1, 2 Lin Ching 1 Ming-Jen Yang 1, 2 Joo-Hong Kim 3 1 Department of Atmospheric Sciences, National Central University, Taiwan 2 Institute of Hydrological and Oceanic Science, National Central University, Taiwan 3 Met Office Hadley Centre, UK

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

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 Wang and Chan (2002) Ho et al. (2005) Camargo and Sobel (2005)

Climate background 2 – Modulation of TC by Tropical Pacific multi-decadal variability • ID 1 (1951– 79) to ID 2 (1980– 2001) Typhoon passage frequency JJAS (1971 -2000) TS+TY (Vmax>17 m/s) (1980 -2001) (1951 -1979) 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) (1980 -2001) (1951 -1979)

Climate background 2 – Modulation of TC by Tropical Pacific multi-decadal variability · Significantly affects the frequency of tropical cyclogenesis (Matsuura et al. 2003). 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 10 N show positive feedback with the SSTA in the central Pacific.

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

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

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

TC-MJO: composite Positions of TC geneses (o) Modulation of TC by MJO · # 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. Cat A B C D

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 12 z A 5 12 z B 9 00 z C 13 18 z E 26 06 z

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 TCinactive 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). Year 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 TC 3 MJO act 27. 4 1 2 2 2 act 25. 1 act 31. 2 act 27. 4 2 2 2 3 act inact 21. 8 19. 9 1 2 1 act 21. 4 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2 2 0 3 inact 25. 2 23. 5 34. 6 0 1 0 2 3 2 5 0 2 act inact 19. 9 32. 8 23. 9 19. 6 27. 4

TC tends to be more active in El Niño developing suppressed La Niña. TC-active. June years : and 1982, 1990, 1997, 2002, in 2004 1994 TC-inactive years : 1996, 1998, 2000, 2005 Normal years : 1983, 1984, 1985, 1986, 1987, 1988, 2006 1989, 1991, 1992, 1993, 1994, 1995, 1999, 2001, 2003, 2006 0 1991 5 2004 3 2002 0 2000 3 1988 1987 1999 3 0 1998 1984 3 1997 1983 0 1982 1995

1. 8 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 3. 4 5 0 2. 25 1. 75 3

TC Name Warming Latitude Warming Longitude Warning Tropical Storm A Conson 15. 7 N 116. 6 E 6/04 06 Z 6/05 12 Z B Chanthu 6. 7 N 141. 7 E 6/05 12 Z 6/09 00 Z C Dianmu 6. 4 N 140. 0 E 6/11 18 Z 6/13 18 Z D Mindulle 13. 0 N 147. 3 E 6/21 18 Z 6/23 12 Z E Tingting 11. 6 N 153. 8 E 6/24 18 Z 6/26 06 Z A B C D E D 23 12 z A 5 12 z B 9 00 z C 13 18 z E 26 06 z

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

MJO cyclonic shear zone Easterly wave → TD-type disturbance Rossby wave A, B →Rossby wave energy dispersion MRGW → TD-type disturbance Monsoon cyclonic shear zone

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 ?

Cyclogenesis Mechanism In June 2004 Rossby wave in easterly flow TC MJO confluence zone Monsoon shear line A yes B yes C yes D yes E yes Rossby wave energy dispersion yes Easterly wave

TC A Warning : 2004/06/04 06 UTC @ 15. 7 N, 116. 6 E Contour 30 -60 OLR Rossby wave in eastery flow TD-type disturbance

TC A Warning : 2004/06/04 06 UTC @ 15. 7 N, 116. 6 E A: 6/04 06 Z Eastery wave Monsoon confluence zone 6/05 12 Z TC B Warning : 2004/06/05 12 UTC @ 6. 7 N, 141. 7 E B: 6/05 12 Z 6/09 00 Z

TC C Warning : 2004/06/11 18 UTC @ 6. 4 N, 140. 0 E B: 6/05 12 Z 6/09 00 Z C: 6/11 18 Z 6/13 18 Z Rosssby wave energy dispersion B Monsoon shear line

TC D Warning : 2004/06/21 18 UTC @ 13. 0 N, 147. 3 E MRGW D: 6/21 18 Z TD-type disturbance 6/23 12 Z

TC E Warning : 2004/06/24 18 UTC @ 11. 6 N, 153. 8 E E: 6/24 18 Z TD-type disturbance Monsoon shear line 6/26 06 Z