Upper Ocean Pre-condition and Its Impact on …photino.cwb.gov.tw/rdcweb/lib/cd/cd01conf/load/GBL_OBSM...Satellite Remote Sensing Lab,Dept.of Atmospheric Sciences, NTU Upper Ocean

Satellite Remote Sensing Lab,Dept.of Atmospheric Sciences, NTU

Upper Ocean Pre-conditionand Its Impact on Typhoons

I-I Lin*, Iam-Fei Pun*,Chun-Chieh Wu*, W. Timothy Liu# ,Ming-Dah Chou~, Rebecca Wu*

* Dept. of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan# Jet Propulsion Lab., NASA, USA

~ National Central University, Taiwan


Outline1. Introduction: Importance of ocean pre-condition

before landfall

2. Ocean Pre-condition (warm ocean eddy) and TC Morakot – impact on precipitation

3. Western North Pacific Eddy Rich Zone and Supertyphoons

4. Conclusions and ITOP Experiment 2010


Factors affecting cyclones’ intensity(e.g. Gray 1979; Emanuel 1999; Emanuel et al. 2004 & many more)

• Ambient ocean (SST + subsurface conditions: D26, UOHC)(Leipper and Volgenau 1972; Shay et al. 2000; Goni and Trinanes 2003; Ginis et al. 2004; Lin et al. 2005; 2008; 2009; Moon et al. 2007; 2008; Pun et al. 2007; Shay and Uhlhorn 2007; Wada and Usui 2007;Halliwell et al. 2008; Mainelli et al. 2008; Goni et al. 2009; Shay et al. 2010……)

• Ambient atmosphere (wind shear etc.)

• Cyclone’s own structure

Upper ocean Heat Content (UOHC) or

TCHP (Tropical Cyclone Heat Potential)


Devastating Cyclone Nargis (2008)

> 130,000 death (Webster, Nature Geo. 2008)


Source: Reuters

Source: Reuters

C

d

Source: Reuters

Catastrophic event (> 130,000 death toll):

RI took place just prior to landfall

Lin et al.

GRL 2009

Killer cyclone Nargis (2008)



Show pre-tc sst and alt



W/m^2 SHF LHF Total

With eddy 27 518 545

No eddy -55 230 175


Warm eddy provides favourable

pre-condition for precipitation

development before landfall




Western North Pacific : vast and complex ocean


20-26∘ N

Lin et al. MWR 2009

13 years’ (1993-2005)

observations


In situ profiles

In situD26 (m)

D26 (m)Climatology

Deepening/shoaling

of D26 (m)

% of deepening/shoaling w.r.t.

climatology

Saomai (2000)

88 58 +30 +52%

Maemi_1 129 63 +66 +105%

Maemi_2 96 63 +33 +52%

Maon 109 63 +46 +73%

Average 106 62 +44 +69%


Emanuel, Nature 1999:‘A mere 2.5∘K cooling near storm core can shut down the entire energy production of typhoon’

Given the observed Uh = 3.3 – 5.6 m/s climatology thickness can’t support intensification to cat. 5 but with +SSHA feature, it is possible

Lin et al. MWR 2008


Given the observed Uh = 3.3 – 5.6 m/s D26_min ~ 90-120m

climatology D26 can’t support intensification to cat. 5 but with +SSHA feature, it is possible

30% of Cat 5 west Pac TCs

(i.e., supertyphoons)

in the past 13 years are fueled by the boosters


Both trends pass 90% significant level

0.15/yr

-0.2/yr

R (cold and warm): -0.47

Time series of MJJASO averaged number of eddy Max. number

min. number

4. The number of warm eddy is ↗ , mainly due to lower bound number going up

5. The number of cold eddy is ↘ , mainly due to upper bound number going down

warm eddy

cold eddy

1. Clear interannual signals on both numbers of warm and cold eddies

2. There are opposite trends in warm and cold eddy counts

3. Both types of eddies seem to be affected by ENSO, especially of cold eddy El Niño year: cold ↘ , warm ↗

Consistent with Hwang et al. 2004

Red: warm eddyBlue: cold eddy

94/95

97/98 02/03


Separate identified eddies into three strength categories by their maximum SSHA:

1. Strong Group 1: |Max. SSHA| ＞ 30cm

2. Moderate Group 2: 20cm≦ |Max. SSHA| ≦ 30cm

3. Weak Group 3: |Max. SSHA| ＜ 20cm

Warm eddies strengthen!!Cold eddies weaken!!

Moderate

Weak

Strong

Abrupt change


Summary:

1. UOTS (e.g., D26, TCHP) can be reasonably constructed in the WNP with refined regressions

2. Automated eddy identifying procedure is developed and successfully detects eddies in the SEZ

3. Subsurface condition in the SEZ becomes more favorable to typhoon intensification

Warm eddy

Cold eddy

number

strength

Intensification tracks (1993-2007/May-Oct) More warm eddies deeper D26 favorable to TC


ITOP (Impact of Typhoon On Pacific)

U.S. ONR &

Taiwan’s NSC

IOP : 20 Aug.- 20 Oct. 2010

From R. C. Lien et al.





• Strategic location of ocean pre-condition (e.g., warm ocean eddy) can have fundamental impact onintensification (e.g., RI) and severely affect subsequent impact on lande.g., Nargis (2008) & Maemi (2003).

• Morakot encountered a well-defined warm ocean eddy just prior to landfall which helped in building up it’s asymmetric convection.

• Western North Pacific as a complex ocean (change in pre-condition):20-26 ∘N : eddy rich zone, boosters exist for supertyphoons.

increasing trend of warm eddy .vs. decreasing cold eddy observed between 1993-2009.

• ITOP Experiment Aug-Oct 2010

Conclusions



5 rules to define eddy:See Poster session P.2.22

Documents

Upper Ocean Pre-condition and Its Impact on …photino.cwb.gov.tw/rdcweb/lib/cd/cd01conf/load/GBL_OBSM...Satellite Remote Sensing Lab,Dept.of Atmospheric Sciences, NTU Upper Ocean