# Presentation: 487685

## 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 

**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***

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

## 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

- 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

- Cold

- 1

- Warm minus Cold

**Climate background**

## Climate background

- ID1 (1951–79) to ID2 (1980–2001)             Typhoon passage frequency

- 2

**TS+TY (Vmax>17 m/s)**

**JJAS (1971-2000)**

**~ 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)**

-       Typhoon formation frequency

**Climate background**

**Notes:**
    From ID1 (1951–79) and ID2 (1980–2001), typhoon passage frequency decreased significantly in the East China Sea and Philippine Sea, but increased slightly in the South China Sea. The time series of typhoon passage frequency over the East China Sea and South China Sea further reveal a regime shift in the late 1970s, while those over the Philippine Sea indicate a continuous downward trend of 9% decade1.
    The interdecadal changes in typhoon tracks are associated with the westward expansion of the subtropical northwestern Pacific high (SNPH) in the late 1970s. The expansion of the SNPH to the southeast coast of Asia may result in a larger elliptic pathway of typhoon migration. This is consistent with the westward shift of the typhoon tracks from ID1 to ID2, resulting in an increase of typhoon passage frequency in the South China Sea and a decrease in the East China Sea. 

## Climate background

- Significantly affects the **frequency of tropical cyclogenesis**
-     (Matsuura et al. 2003).

- 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.

**Climate background**

## ENSO 

**ENSO**

**Decadal Variability**
- Seasonal mean genesis location
- and tracks

- Eq

- High level

- Low level

- warm

- cold

- Seasonal mean genesis location

## General mechanism is similar!

**Decadal Variability**

- Seasonal genesis number
- Seasonal mean genesis location and tracks

##   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 **wes**terly phase*.

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

**TC-MJO: composite**

## Positions of TC geneses (o)

**Positions of TC geneses (****o****)**

**Category**
**A**
**B**
**C**
**D**

******  ****M****odulation ****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.

**TC-MJO: composite**

**Notes:**
TD-type synoptic waves (i.e., 3–10 days) [e.g., Lau and Lau (1990); Takayabu and Nitta (1993); Chang et al. (1996)], which may be initiated by the scale contraction of mixed Rossby–gravity (MRG) waves within a monsoon confluent region (e.g., Sobel and Bretherton 1999; Kuo et al. 2001; Dickinson and Molinari 2002; Aiyyer and Molinari 2003) or by Rossby wave energy dispersion in the wake of a preexisting TC (e.g., Briegel and Frank 1997; Ritchie and Holland 1999; Sobel and Bretherton 1999; Li et al. 2003; Li and Fu 2006), and the intraseasonal variability of the monsoon circulation and convection that have submonthly time scales (e.g., Hartmann et al. 1992; Fukutomi and Yasunari 1999; Delk 2004; Ko and Hsu 2006).

## 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. 

- 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.

**June 2004 vs Climate**

## 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).

| Year  | 1982  | 1983  | 1984  | 1985  | 1986 | 1987 | 1988  | 1989  | 1990  | 1991 | 1992  | 1993 |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| TC  | 3  | 1  | 2  | 2  | 2  | 2  | 2  | 2  | 3  | 1  | 2  | 1  |
| MJO  | act  27.4  |  | act  25.1  | act  31.2  | act  27.4 | act  21.8  | inact 19.9 |  |  | act  21.4  |  |  |
| 1994 | 1995  | 1996  | 1997 | 1998  | 1999  | 2000  | 2001  | 2002  | 2003  | 2004  | 2005  | 2006  |
| 2  | 2  | 0  | 3  | 0  | 1  | 0  | 2  | 3  | 2  | 5  | 0  | 2  |
|  | inact 25.2 | inact 23.5 | inact 34.6  |  |  |  |  | act  19.9 | inact 32.8  | act  23.9 | inact 19.6 | inact 27.4 |

## TC tends to be more active in El Niño developing June and suppressed in La Niña.

- 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

**1982**

**1987**

**1991**

**1994**

**1997**

**2002**

**2004**

**2006**

**1983**

**1984**

**1995**

**1988**

**1998**

**1999**

**2000**

## 1.8

- 3.4

- 0

- 5

- 1.75

- 2.25

- 3

- 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

## Slide 14

| TC | Name | Warming Latitude  | Warming Longitude  | Warning  | Tropical Storm |
| --- | --- | --- | --- | --- | --- |
| A | Conson | 15.7N | 116.6E | 6/04 06Z | 6/05 12Z |
| B | Chanthu | 6.7N | 141.7E | 6/05 12Z | 6/09 00Z |
| C | Dianmu | 6.4N | 140.0E | 6/11 18Z | 6/13 18Z |
| D | Mindulle | 13.0N | 147.3E | 6/21 18Z | 6/23 12Z |
| E | Tingting | 11.6N | 153.8E | 6/24 18Z | 6/26 06Z |

## Total OLR  (5N-15N)

- Black line : MJO
- Green line : Rossby wave
- Purple line : MRG wave

## Easterly wave →

- Easterly wave →
- TD-type disturbance

- Rossby wave

- A, B →Rossby wave energy dispersion

- MRGW →
- TD-type disturbance

- TD-type disturbance

- Monsoon cyclonic shear zone

- MJO 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

| TC | MJO 
confluence zone | Monsoon shear line | Rossby wave                  
energy dispersion   | Easterly wave |
| --- | --- | --- | --- | --- |
| A | yes |  |                                        | yes |
| B | yes |  |                                        | yes |
| C | yes | yes | yes                                     |  |
| D |  | yes |                                           |  |
| E |  | yes |                                            |  |

**Cyclogenesis Mechanism**
**In June 2004**

- Rossby wave in easterly flow

## TD-type disturbance

- Rossby wave
- in eastery flow

- TC A
- Warning : 2004/06/04 06UTC @ 15.7N, 116.6E

- Contour 30-60 OLR

## Eastery wave

- TC B
- Warning : 2004/06/05 12UTC @ 6.7N, 141.7E

- Monsoon confluence zone

| A: 6/04 06Z | 6/05 12Z |
| --- | --- |

| B: 6/05 12Z | 6/09 00Z |
| --- | --- |

- TC A
- Warning : 2004/06/04 06UTC @ 15.7N, 116.6E

## TC C

- Warning : 2004/06/11 18UTC @ 6.4N, 140.0E

- Rosssby wave
- energy
- dispersion

- Monsoon shear line

| C: 6/11 18Z | 6/13 18Z |
| --- | --- |

| B: 6/05 12Z | 6/09 00Z |
| --- | --- |

## MRGW

- TC D
- Warning : 2004/06/21 18UTC @ 13.0N, 147.3E

- TD-type disturbance

| D: 6/21 18Z | 6/23 12Z |
| --- | --- |

## TC E

- Warning : 2004/06/24 18UTC @ 11.6N, 153.8E

- TD-type
- disturbance

- Monsoon shear line

| E: 6/24 18Z | 6/26 06Z |
| --- | --- |