The formation and dynamics of cold-dome northeast of Taiwan 報告人：沈茂霖 (Mao-Lin Shen) 2015/5/17 Seminar report

The formation and dynamics of cold-dome northeast of Taiwan

報告人：沈茂霖　　　　 (Mao-Lin Shen)

112/04/18

Seminar report

112/04/18 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 2

Outlines

Domain describtion Observations Numerical results and mechanic discussions Conclusions


Numerical Model

120oE 121oE 122oE 123oE 124oE 125oE 24oN

25oN

26oN

27oN

28oN L

atitu

de

Longitude

200

400

600

800

1000

1200

1400

1600

1800

Fig. 1b. Schematic of the study region.

MHC

NMHC


Observations

Microwave (MW) and InfraRed (IR) merged Sea Surface Temperature (SST) provided by Remote Sensing Systems (RSS)

MW and IR merged SST data available on 0.09°×0.09° spatial resolution over the global region (±90°) .

Time-longitude SST anomalies in the north of Taiwan and four events were checked.

Argo data.


Fig. Time-longitude plot of SST anomalies in the north of Taiwan (25.4°N-25.9°N).

2007

2008

2009


Observations

Fig. 2. SST results.

1 Oct 2007 18 Oct 2007

16 May 2008 23 Sep 2008


Observations

Fig. 3. The temperature contour and velocity fields at depth 6m on day 157 and 226, Year 37.

Day 157 Day 226


Observations

118oE 120oE 122oE 124oE 126oE 128oE 22oN

24oN

26oN

28oN

30oN

32oN

Fig. 4. The Argo data since 3 Aug 2001 to 6 Sep 2009, and only 2047 data are available.


Observations

3 3 .5 3 4 3 4 .5 3 5 3 5 .5

S a l

4 0 0

3 5 0

3 0 0

2 5 0

2 0 0

1 5 0

1 0 0

5 0

0

pres

sure

(db

r)

3 4 3 4 .2 3 4 .4 3 4 .6 3 4 .8 3 5

S a l

0

5

1 0

1 5

2 0

2 5

3 0

3 5

T (o C

)

Fig. 5. The Argo data measured on Kuroshio main stream, in which has maximum salinity larger than 34.7 [Chuang et al, 1993], totally 9 profiles in JJA.


Observations

1 2 1 6 2 0 2 4 2 8

T ( oC )

2 0 0

1 5 0

1 0 0

5 0

0

pres

sure

(db

r)

0 4 D ec0 8 D ec1 2 D ec1 6 D ec

3 4 3 4 .2 3 4 .4 3 4 .6 3 4 .8 3 5

S a l

2 0 0

1 5 0

1 0 0

5 0

0pr

essu

re (

dbr)

0 4 D ec0 8 D ec1 2 D ec1 6 D ec

3 4 3 4 .2 3 4 .4 3 4 .6 3 4 .8 3 5

Sa l

0

5

1 0

1 5

2 0

2 5

3 0

3 5

T (o C

)

0 4 D ec0 8 D ec1 2 D ec1 6 D ec

Fig. 7. Argo data taken from the float WMO No. 2900797.


Observations

1 6 2 0 2 4 2 8

T ( oC )

2 0 0

1 5 0

1 0 0

5 0

0

pres

sure

(db

r)

1 3 Ju ly1 7 Ju ly2 0 Ju ly2 4 Ju ly

3 4 .0 3 4 .2 3 4 .4 3 4 .6 3 4 .8 3 5 .0

S a l

2 0 0

1 5 0

1 0 0

5 0

0pr

essu

re (

dbr)

1 3 Ju ly1 7 Ju ly2 0 Ju ly2 4 Ju ly

3 4 .0 3 4 .2 3 4 .4 3 4 .6 3 4 .8 3 5 .0

Sa l

0

5

1 0

1 5

2 0

2 5

3 0

3 5

T (o C

) 1 3 Ju ly1 7 Ju ly2 0 Ju ly2 4 Ju ly

Fig. 8. Argo data taken from the float WMO No. 2900819.

Typhoon Kalmaegi 7/16~7/18


Observations

Many events (local winds variation, typhoons, or winter intrusion of Kuroshio) merged with the cold-dome variation and make the analysis difficult.

Fewer field measures to have a good comprehension. Lack of current velocities. Few information was

carried by Argo trajectories.

Of WMO No. 2900797, the vertical temperature difference are about 3-5 on 12 Dec and 16 Dec .℃


Numerical results

No special events interrupted. Current velocities clearly identified. Three spots were considered: Taiwan Strait Water (TS

W), Cold-Dome Water (CDW), Kurioshio Surface Water (KSW).

Temperature variation Motion of water parcel Influence of topography change Effect of wind-driven upwelling


Numerical results

2 0

2 2

2 4

2 6

T (o C

)

Jan F eb M ar A p r M ay Ju n Ju l A u g S ep O c t N o v D ec

C D WT S WK S WK d 5 4

Fig. 12. Temperature comparison of the three selected boxes. Upper 30 m averaged was taken.


Numerical results

Fig. Motion of flow particle in Kuroshio Subtropical Water.


Topography change

Fig. Comparison of flow field and temperature contour of different topography.

Origional

(FO)

Depth = 80 m

(F080)

Depth = 100 m

(F100)

Depth = 60 m

(F060)


Topography change

2 2

2 3

2 4

2 5

2 6

T (o C

)


F OF 0 6 0F 0 8 0F 1 0 0

2 3 .5

2 4

2 4 .5

2 5

2 5 .5

2 6

T (o C

)


F OF 0 6 0F 0 8 0F 1 0 0

Fig. 16. Temperature comparison among three marked region of the four numerical experiments.

2 2

2 3

2 4

2 5

2 6

T (o C

)


F OF 0 6 0F 0 8 0F 1 0 0

TSW

KSW

CDW


Numerical results

-0 .2

0 .0

0 .2

0 .4

w (

m/d

ay)

Jan F e b M ar A p r M ay Ju n Ju l A u g S e p O c t N o v D e c

C D WT S W -0 .0 0 8

-0 .0 0 4

0 .0 0 0

0 .0 0 4

0 .0 0 8

T

(o C)

Jan F e b M a r A p r M a y Ju n Ju l A u g S e p O c t N o v D e c

C D WT S W

Fig. (a) upwelling velocities of TWS and CDW, and (b) the wind-induced temperature difference variation.

(a) (b)


Numerical results

Fig. 13. Temperature difference comparison: (a) the total one of TSW and CDW; (b) the convection-induced one of TSW and CDW; (c) the vertical temperature difference on depth 6 m and on depth 54 m of TSW, CDW, and KSW, respectively.

-0 .3

-0 .2

-0 .1

0 .0

0 .1

0 .2

0 .3

dT/d

t (o C

/day

)


C D WT S W

-0 .8

-0 .4

0 .0

0 .4

0 .8

dT/d

t (o C

/day

)


C D WT S W

-2

-1

0

1

2

3

T

(o C)


C D WT S WK S W


Numerical results

Fig. Cross-correlation of temperature difference: blue line, the total one and the convection one; red line, the total one and the turbulent diffusive one.


Numerical results

Fig. 3. The temperature contour and velocity fields at depth 6m on day 157 and 226, Year 37.

Day 157 Day 226


Conclusions

Formation of cold-dome of northeast Taiwan is combined by many regional effects, such Kuroshio axis migration, topography change, wind-driven upwelling, vortex shedding, ocean surface mixing.

Main mechanics of the formation was verified by numerical experiments, in which special events were not considered.

Wind-driven upwelling introduces little temperature variation except typhoon events.


Conclusions

Topography plays a main role in this region. Numerical experiments show that TSW dominates northeast Taiwan while bathymetry shallower than original one.

Convection has faster influence, and turbulent diffusion has more contribution. However, it also denotes the cold-dome can be disturbed easily.

The cyclonic eddy reserves the cold water.


Thank you for your attention.

Documents

The formation and dynamics of cold-dome northeast of Taiwan 報告人：沈茂霖 (Mao-Lin Shen) 2015/5/17 Seminar report